The Scary Side of Sunscreen

The sun is shining and you’re about to make the responsible choice to slather on some sunscreen to protect your skin from the sun’s harmful (but also warm and wonderful) UV rays. Even the smell of sunscreen elicits summertime nostalgia for many of us. However, safety concerns have been raised regarding some of the most common ingredients in traditional sunscreens.

It’s an unfortunate paradox: protect yourself from skin cancer and expose yourself to the harmful ingredients in the sunscreen or forego the sunscreen and potential chemical exposure to roll the dice with UV ray-related cancers like melanoma. Thankfully, there is a growing body of toxicity data to help guide decision-making when choosing how to protect your skin from the sun!

What’s wrong with my sunscreen?

Many of the most popular ingredients in sunscreen have received scrutiny for their toxicity towards humans and the environment. Oxybenzone is the compound that has achieved the most notoriety thus far after it was reported that it can be found in the blood of nearly 100% of Americans, including in breastmilk. Oxybenzone is a common ingredient in sunscreen because it absorbs damaging ultraviolet (UV) rays and is considered to provide broad-spectrum coverage, meaning it can protect skin from both UVB and short-wave UVA rays. Not only is oxybenzone exposure ubiquitous, but this chemical is also capable of disrupting hormone signaling in humans and is a common skin allergen for sensitive populations. Other common ingredients, such as octinoxate and homosalate, are also detectable in breastmilk and have both been reported to similarly disrupt hormones in humans.

A handy visual guide adapted from Environmental Working Group (EWG) showing the toxicity rankings of common sunscreen ingredients.

In addition to these human health concerns, there are also important environmental concerns to take into consideration. A recent review of the literature reported that common sunscreen ingredients (oxybenzone, octocrylene, and octinoxate, among others) are detectable in nearly all water sources sampled from around the world and these chemicals are extremely difficult to remove from the water via traditional wastewater treatment. These chemicals have been detected in aquatic wildlife and have been linked to coral bleaching. In fact, Hawaii and Florida have recently passed legislation banning the use of sunscreens containing chemicals like oxybenzone to help protect precious marine ecosystems as well as improve human health.

Is sunscreen worth the risk?

YES. An estimated 1 in 5 Americans will develop skin cancer by age 70 and regular daily use of sunscreen that is SPF 15 or greater reduces the risk of developing melanoma by 50 percent. While the risks associated with some of the active ingredients of sunscreen are not ideal, it is probably better than foregoing sunscreen altogether. However, there are sunscreen-free options for protecting yourself from UV damage. For example, wearing SPF-rated long-sleeved clothing and wide-brimmed hats or simply avoiding excess sunlight exposure whenever possible can be lifestyle changes that reduce the need for sunscreen usage. It is important to note that both protective clothing and avoiding sun exposure can only do so much to protect your skin and that there will always be circumstances under which sunscreen is the most appropriate skin protectant to implement.

So what kind of sunscreen should I be using?

Sunscreens impart their UV protection through two main mechanisms: chemical and physical. Most of the troublesome sunscreen ingredients are chemical barriers to UV rays. The sunscreen ingredients that impart the best UV coverage and act as a physical barrier are mineral-based, like zinc oxide and titanium dioxide. So far, the existing toxicity data suggest that zinc oxide and titanium dioxide sunscreens are relatively safe for us and for the environment!

Here is a visual guide to UV protection based on the sunscreen ingredients, shared from Reef Repair.

For more information to help your decision making on sunscreen protection, visit EWG’s page for a comprehensive guide!

Peer edited by Julia DiFiore.

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Fun Facts about the Cutest Baby Animals of Spring, and how they Contribute to Science

Spring is officially here, so it’s time for some science about some of the most adorable baby animals. In my past training as an animal scientist at UC Davis, spring was largely marked by births within all the herds at our campus animal facilities. As a teaching assistant for the Animal Science department, I enjoyed interacting with these new additions and teaching future animal scientists how to safely practice animal husbandry. Considering the proximity of this post to the start of spring, I thought it fitting to discuss some of the history behind our most beloved spring animals and how they’ve contributed to science. Be the hit at your next cocktail party (or perhaps an Easter brunch) with these fun facts!

Rabbits and Kits

        Rabbits and hares may be some of the most iconic symbols of spring, and they’re probably best associated with the season through tales of the Easter bunny. According to folklore, the hare was the sacred animal of the Germanic goddess of spring, Eostre. There are multiple legends through which Eostre is believed to have created the Easter hare. In one version, Eostre transformed a bird with frozen wings into a rabbit, allowing the resulting animal to retain its ability to lay eggs. In another version of the legend, Eostre became annoyed with a bird which prided itself on laying the most beautiful eggs, so she transformed the bird into a rabbit; in a moment of mercy, she allowed the rabbit to lay its eggs once per year, in the spring. No matter what you believe, it’s undeniable that rabbits and spring are a classic combination, and rightfully so, as their rapid proliferation easily casts them as symbols of fertility.

A rabbit standing on its hind legs in a field.
Rabbits are often associated with spring through tales of the Easter bunny, but their biology also aids scientific discovery!

        Rabbits are extremely prolific. In terms of their reproductive behavior, rabbits are classified as induced ovulators, meaning they ovulate after sexual stimulation. Rabbits also have a relatively short gestation, or pregnancy, lasting about 28-32 days. This short gestation period in addition to induced ovulation means that a reproductive female is capable of giving birth, or kindling, a new litter of kits as often as once per month. Over the course of one rabbit’s seven-year lifespan, a single female and her female descendants could produce over 100 billion new female rabbits! It’s no wonder these animals are associated with spring, a season marked by new life.

        Besides their connection to spring, rabbits have also contributed to science as important model organisms. Rabbits provided the first model for cancer caused by a virus, which has been crucial for better understanding how human papillomaviruses (HPVs) cause cancer and in the development of vaccines against HPV infection. In addition, rabbits are commonly used to produce antibodies for laboratory use, such as for immunology and infectious disease research. Rabbits were also used in the development of certain vaccines, including the rabies vaccine, and surgical laser technologies. Finally, their physiology makes them ideal for studying several of the diseases plaguing humans, including cholera, cystic fibrosis, eye and ear infections, and non-infectious conditions such as those resulting from high cholesterol.

Chickens, Chicks, and Eggs

        Chickens and the eggs and chicks they produce also hold special significance for the spring season. Similar to rabbits, chicks and eggs have been regarded as symbols of spring, reproduction, and new life, even in civilizations as far back as ancient Rome. In Catholicism, eggs came to be associated with spring, and particularly Easter, though the practice of Lent. Traditionally, fasting practices during Lent excluded the consumption of all animal products, including eggs. As lent ends with Easter, spring may additionally be associated with an abundance of eggs as a result of the holiday.

        Another reason why chicks and eggs may be particularly associated with spring could be due to the unique laying cycle of hens. The avian reproductive cycle is stimulated by increased hours of daylight, as is characteristic of spring time. More specifically, light passing through the eye or skull of birds can be received by photoreceptors in the hypothalamus, which then activates the pineal gland, which in turn triggers the hormonal cascade that results in the production of eggs. If those eggs are fertilized by the passing rooster, then increased daylight hours mean more cute, fuzzy chicks!

A young chicken (chick) in a field.
In nature, hens lay eggs more frequently with increasing light hours. This means that spring brings more cute (and sassy?) chicks!

        Aside from the chicken’s ubiquitous use as an agricultural animal, chickens and their eggs have also helped scientists in the biomedical field! Eggs are the most common means of producing flu vaccines; the flu virus may be injected into eggs, allowed to replicate, and after several days these viral particles can be removed from the egg and heat inactivated to produce new flu vaccines. Current research with genetic engineering technologies has expanded the contribution of chickens to science, as researchers at the Roslin Institute in Scotland have now produced birds capable of producing and secreting medicinal antibodies into their eggs. These antibodies have the potential to treat diseases including melanoma and multiple sclerosis.

Sheep and Lambs; Goats and Kids

        Finally, near and dear to my own heart, are lambs (young sheep) and kids (young goats). Having raised sheep in high school and performed research with goats and goat milk while working towards my Master’s, I relish any chance to talk about them. While lambs are a frequent biblical symbol associated with Easter, goats are a similar species also born in the spring, and goats have become quite the rage nowadays with activities such as baby goat festivals, goat yoga, goat party rentals, and even goat-kart races!

A young goat kid standing on top of its mother.
Everyone is raving about goats these days, and it’s easy to see why! Who wouldn’t want to spend a beautiful spring day with these rambunctious cuties?

Within minutes after birth, lambs and kids are capable of walking, and one of the first items on their mind is food! Lambs and kids are both classified as ruminants, which means they have a specialized digestive system to help break down a plant-based diet. Ruminants have a single stomach with four compartments: the reticulum for temporary storage and size-sorting of feed, the rumen with its vast microbial population for fermentation of fiber, the omasum for water absorption, and the abomasum, which is akin to our own acidic stomach and helps with the chemical breakdown of food. Because lambs and kids are mammals like us, they solely consume milk for the first few weeks to months of their life. However, the microbial population in the rumen can potentially alter the nutrient composition of the milk and reduce its nutritional value for the offspring. So how do baby goats and sheep get around this hurdle? They have a specialized structure in early development, termed the esophageal or reticular groove, which bypasses the microbes within the rumen and allows milk to be broken down and digested directly from the abomasum. Isn’t that neat? Ruminants are the coolest!

Young lambs nursing off of their mother in a field.
Young lambs enjoying a meal from mom; ruminants like sheep and goats must use specialized digestive structures early in life to maximize the nutrition they receive from milk.

Sheep and goats have also been crucial contributors to science. The aforementioned Roslin Institute is responsible for the first cloned mammal, Dolly the Sheep. Cloning of the first mammal helped pave the way for other genetic modifications in livestock. In previous years, milk from genetically engineered goats has been produced to include supplemental antimicrobial enzymes, such as lysozyme, in efforts to fight childhood malnutrition and diarrhea. Today, genetically engineered sheep are potential candidates for human organ generation due to their similar size and physiology to humans.        

While spring is a time to enjoy the company of new furry, feathered, or woolen companions, it may also be a time to reflect on how all these species have contributed to science and the wellbeing of humans. So the next time you go to the grocery store to support your favorite animal industry, go to an event at your local farm, or attend your favorite goat yoga class, know that your efforts also support science!

Peer edited by Gabby Budziszewski.

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Flossing your way to cancer

Toxins are everywhere these days. In your water, in your food, in your beauty products, in mostly everything you consume or surround yourself with. Most importantly, toxins are in the headlines. The media has done a great job sensationalizing many toxicology papers and creating eye-catching headlines, like mine, that are not necessarily correct.

Earlier this year, USA Today released an article titled “Oral-B Glide floss tied to potentially toxic PFAS chemicals, study suggests” and Medical News Today released a similar piece titled “Flossing could increase exposure to toxic chemicals”. These were all based on a recent article published using self-reported data from the Child Health and Development Studies in Oakland, CA. Due to the media sensationalizing this study, it is important to break down the headlines and understand what was actually said and done.

Figure 1. Structure of PFOA: a non-polymer PFAS

Figure 2. Structure of PFOS: a non-polymer PFAS

Figure 3. Structure of PFTE: a polymer PFAS. n signifies that this basic chemical unit is repeated multiple times to form a polymer.

The toxins of focus in the article, as the USA Today headline states, are PFAS. PFAS, short for per- and polyfluoroalkyl substances, are man-made chemicals that have been used in industry and consumer products for nearly 70 years. PFAS are fluorosurfactants which are a group of chemicals whose properties originate from a substitution of hydrogen with fluorine along the carbon backbone. PFAS include chemicals like PFOA, PFOS, and GenX and can be found in non-stick cookware, water-repellent materials, some cosmetics, food packaging, and products that resist grease, water, and oil. PFAS encompass many substances and the EPA has a list that includes over 5000 PFAS substances. The PFAS substances can be divided into two major families: polymer and non-polymer. Polymers and non-polymers are differentiated from each other by size, with polymers being a chemical made of many repeating units of non-polymers. The non-polymer PFAS include PFOA and PFOS and are the most commonly detected in the environment. The polymer PFAS are larger molecules than the non-polymer substances and include PFTE.

In the study described, they measured a total of 11 non-polymer PFAS (including PFOA and PFOS) in blood samples in 178 middle-aged women and collected data on behaviors that they believed would influence PFAS exposure. These behaviors included using things like non-stick cookware, microwave popcorn, glide floss (Oral-B), coated cardboard containers, seafood, and stain-resistant carpet and furniture. This is the first paper to consider dental floss as an exposure to PFAS. To narrow down the brand and type of floss, the researchers did something interesting. They analyzed 18 different floss types for the presence of fluorine and used it to evaluate the plausibility of PFAS exposure from dental floss. They found Oral-B Glide dental floss and two other dental floss products to have detectable levels of fluorine.

Fluorine is a chemical that is represented by the letter F on the periodic table of elements. We commonly know it as fluoride, which is made when you combine fluorine and a metal, like sodium. Fluoride can be a common component in many of our dental products, although Oral-B’s website does not specify whether their Glide floss contains any. They do have an instructional page that takes you through the different types of dental floss, where you can see a very familiar looking word: polytetrafluoroethylene (PTFE). PTFE is the most commonly used chemical for Teflon coating and is in the polymer family of PFAS which is not the same class as PFOA and PFOS (these are non-polymers).

The article does take notice of the report that Oral-B Glide is manufactured from PTFE; however, it is confusing why they chose to evaluate PFAS non-polymer exposure when the Oral-B Glide Floss is made with PTFE which is a PFAS polymer. It is particularly perplexing since the studies that describe the toxicity of PTFE are few in number, in comparison to PFOA, and the results do not present substantial conclusions. This is when a little chemistry knowledge is needed. PFOA is commonly used in the synthesis of PTFE and is an established dangerous chemical. Additionally, PTFE may also contain PFCA (another type of PFAS). The studies done to assess the presence of these PFAS in PTFE were done with non-stick pans while applying high levels of heat to see if PFOA and PFCA gases were released. It seems a stretch to imagine that dental floss would undergo enough heat to release these more dangerous toxins and thus contribute to the circulating levels of non-polymer PFAS. However, it is possible that PFTE, when metabolized by the body, breaks down into these more toxic metabolites.

It is mentioned in the discussion of the article that “PFASs are detected in PTFE-based dental floss…” and cites two papers. One of the papers clearly shows that PFOA was detected in both dental floss and dental tape. However, the concentration is minute in comparison to PFTE cookware, PFTE film/sealant tape, and popcorn bags. There is one main thing to keep in mind from this seemingly damning paper. It is unclear from their methods how they measured the PFOA in the dental floss/tape, but it is clear that it was not under circumstances that would mimic human use. The researchers for this paper note that since “…PFTE does not dissolve…” you have to measure PFOA presence by extracting from a ground or powdered material.

All in all, it is important for studies to assess the potential sources of exposure and hold industry accountable. However, it is important when evaluating new sources of exposure to be sure that the exposure in question could be significantly contributing to your toxins of interest. For the case of Oral-B Glide, it is possible that the PTFE used in this dental floss is contributing to elevated levels of PFAS in people’s bloodstream. Nevertheless, we currently do not have the research to support this connection, and so it is important to be mindful with our results and not let the media sensationalize them.

Peer edited by: Isabel Newsome and Nicholas Martinez.

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The Science Behind Spitting for your At-home Genetic Test

Conjuring up two milliliters of spit after not eating/drinking 30 minutes prior doesn’t sound taxing, but give it a try, and you’ll quickly change your mind. Four years ago, I sat in my kitchen wafting the scent of freshly baked brownies into my face in an attempt to make myself salivate. Voilá! I finally produced enough spit for my 23andMe kit and rewarded myself with a brownie. In 6-8 weeks, I would learn more about my health and ancestry, all thanks to just two milliliters of saliva. Best Christmas gift ever…thanks, mom and dad!

Popularity for these at-home genetic testing kits has soared in recent years. For example, AncestryDNA sold about 1.5 million kits in three days alone last fall. People love buying these DNA kits as a holiday gift, and it’s one of Oprah’s favorite things, so why wouldn’t you want to purchase one? Given the general affordability of these non-invasive tests and the variety of kits to choose from, it’s easy to participate in the fun. &

After scientists receive your at-home genetic kit, they isolate cells from your saliva and unravel the chromosomes in your DNA. Then they read your base pairs like a book and check for specific genetic markers that indicate risk of a certain disease. Your ancestry is determined by comparing your genetic markers to a reference database.

I’m amazed that information about my ancestors’ migration pattern is extracted from the same fluid that helped disintegrate the brownie I just ate. In addition to the enzymes that aid in digestion, human saliva contains white blood cells and cells from the inside of your cheeks. These cells are the source of DNA, which is packaged inside your chromosomes. Humans carry two sex chromosomes (XX or XY) and 22 numbered chromosomes (autosomes). Chromosomes are responsible for your inherited traits and your unique genetic blueprint. During a DNA test, scientists unravel your chromosomes and read the letters coding your DNA (base pairs) to check for specific genetic markers.

Companies perform one or multiple kinds of DNA tests, which include mitochondrial DNA (mtDNA), Y-chromosome (Y-DNA), or autosomal DNA. An mtDNA test reveals information about your maternal lineage since only women can pass on mitochondrial DNA. mtDNA codes for 37 out of the 20,000-25,000 protein-coding genes in humans. Y-DNA test is for male participants only and examines the paternal lineage. This DNA accounts for about 50-60 protein-coding genes. Autosomal DNA testing is considered the most comprehensive analysis, since autosomes include the majority of your DNA sequences and the test isn’t limited to a single lineage. However, companies don’t fully sequence your genome because then the at-home kits could no longer be affordable. Instead the tests look at about 1 million out of 3 billion base pairs.

But how reliable are these tests if less than one percent of your DNA is sequenced? When detecting genetic markers that could increase disease risk, these tests are very accurate since scientists are searching for known genes associated with a certain disease. However, the reliability of predicting your ancestry is another story.

Using DNA to determine ethnicity is difficult since ethnicity is not a trait determined by one gene or a combination of genes. Scientists analyze only some of your genome and compare those snippets of DNA to that of people with known origins. For example, Ancestry uses a reference panel that divides the world into 26 genetic regions with an average of 115 samples per region. If your results show that you’re 40% Irish, then that means 40% of your DNA snippets is most similar to a person who is completely Irish. Each company has their own reference database and algorithm to decide your ethnic makeup, so it’s likely that you would receive different results if you sent your DNA to multiple companies.

At-home genetic tests are an exciting and affordable way to explore the possibilities of your genetic makeup and can paint a general picture of your identity. While the specifics of the ethnicity results may be a bit unreliable, at least it’s a good starting point if you’re interested in building your family tree!

Peer edited by Nicole Fleming.

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Understanding the 2017 Climate Science Special Report

Earlier this year, the U.S. government released the Climate Science Special Report.  This document describes the state of the Earth’s climate, specifically focusing on the U.S.  If you are someone who is interested in environmental science or policy, you may have thought about reading it.  But where to start? The report contains fifteen chapters and four additional appendices, so reading it may seem daunting.  We published this summary of the report to provide a brief introduction to climate change, and to provide a starting point for anyone who wants to learn more.

Retreating of Lyell Glacier (Yosemite National Park) in 1883 and 2015. Park scientists study glaciers to understand the effects of climate change in parks serviced by the National Parks Service. 1883 Photo: USGS Photo/Israel Russell 2015 Photo: NPS Photo/Keenan Takahashi













What is Climate Change?      

“Climate change” is a phrase that has become ubiquitous throughout many aspects of American and global society, but what exactly is climate change?

Like weather, climate takes into account temperature, precipitation, humidity, and wind patterns.  However, while weather refers to the status of these factors on any given day, climate describes the average weather for a location over a long period of time.  We can consider a climate for a specific place (for example, the Caribbean Islands have a warm, humid climate), or we can consider all of Earth’s climate systems together, which is known as the global climate.

Depending on where you live, you may have seen how weather can change from day to day.  It may be sunny one day, but cool and rainy the next.  Climate change differs from changes in weather because it describes long-term changes in average weather. For example, a place with a changing climate may be traditionally warm and sunny, but over many years, become cooler and wetter.  While weather may fluctuate from day to day, climate change is due to gradual changes that occur over long periods of time.  Climate is viewed through an historical lense, comparing changes over many years. Though we may not notice the climate changing on a daily basis, it can have drastic effects on our everyday lives.  It can impact food production, world health, and prevalence of natural disasters.,_plotted_against_changes_in_global_mean_temperature.png

Summary of the potential physical, ecological, social and large-scale impacts of climate change. The plot shows the impacts of climate change versus changes in global mean temperature (above the 1980-1999 level). The arrows show that impacts tend to become more pronounced for higher magnitudes of warming. Dashed arrows indicate less certainty in the projected impact and solid arrows indicate  a high level of certainty.

What Causes Climate Change? 

The major factor determining the Earth’s climate is radiative balance.  Radiation is energy transmitted into and out of the Earth’s atmosphere, surface, and oceans.  Incoming radiation most often comes from light and heat energy from the Sun.  Earth can lose energy in several ways.  It can reflect a portion of the Sun’s radiation back into space.  It can also absorb the Sun’s energy, causing the planet to heat up and reflect low-energy infrared radiation back into the atmosphere.  The amount of incoming and outgoing radiation determines the characteristics of climate, such as temperature, humidity, wind, and precipitation.  When the balance of incoming and outgoing radiation changes, the climate also changes.,_2012).png

Scientists agree that it’s extremely likely that human activity (via greenhouse gas emissions) is the dominant cause of the increase in global temperature since the mid-20th century.

There are some natural factors that can influence climate.  The main ones are volcanic eruptions and the El Niño Effect.  Volcanic eruptions emit clouds of particles that block the Sun’s radiation from reaching the Earth, changing the planet’s radiative balance and causing the planet to cool. The El Niño Effect is a natural increase in ocean temperature in the Pacific Ocean that leads to other meteorological effects.  The increase in ocean temperature off the coast of South America leads to higher rates of evaporation, which can cause wind patterns to shift, influencing weather patterns worldwide. Together, these factors influence climate, so when they differ from the norm, they can contribute to climate change.

It is true that climate change can occur naturally and it is expected to happen slowly over long periods of time.  In some cases, the climate can change for a few months or years (such as in the case of a volcanic eruption), but the effects of these events are not long-lasting.  However, since the Industrial Era, the factor contributing most to climate change has been an anthropogenic driver, meaning one that is being caused by human activity. The primary cause of climate change since the Industrial Era has been the presence of greenhouse gases in the atmosphere.  The main greenhouse gases are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).  These gases are problematic because they remain in the Earth’s atmosphere for a long time after they are released.  They trap much of Earth’s outgoing radiation, leading to an imbalance of incoming and outgoing radiation energy.  Because the Earth’s atmosphere is holding on to all that energy while still receiving irradiation from the Sun, the planet heats up.  This is called the greenhouse effect, because it is similar to what happens in a greenhouse—the Sun’s energy can get in, but the heat cannot get out.  The greenhouse effect has intensified due to the greenhouse gases that are released during our modern industrial processes.  This has caused the Earth’s climate to begin to change.


Who contributed to the Climate Science Special Report?

The report was written by members of the American scientific community, including (but not limited to) the National Science Foundation, the National Aeronautics and Space Administration (NASA), the US Army Corps of Engineers, and multiple universities and national labs.  They analyzed data from articles in peer reviewed scientific journals—that is, other scientists read these articles before they were even published to check for questionable experiments, data, or conclusions—as well as government reports and statistics and other scientific assessments.  The authors provided links to each source in citation sections at the end of each chapter. They combined everything they learned into this one comprehensive document, the Climate Science Special Report.

What can we learn from this report?      

First of all, the report reveals that the Earth is getting warmer.  The average global surface temperature has increased about 1.8°F (1.0°C) since 1901.  This may seem like a small change, but this increase in temperature is enough to affect the global climate.  Sea levels have risen about eight inches since 1900, which has led to increased flooding in coastal cities.  Weather patterns have changed, with increased rainfall and heatwaves.  While the increased rainfall has been observed primarily in the Northeastern U.S., the western part of the U.S. has experienced an increase in forest fires, such as those that have devastated California this year.  Such changes in weather patterns can be dangerous for those who live in those areas.  They can even damage infrastructure and affect agriculture, which impacts public health and food production.  These changes mainly result from greenhouse gases, namely CO2, that humans have emitted into the atmosphere.

Where can I go to read the report myself?  

You can find a link to the main page of the report here.  There is also an Executive Summary, which was written for non-scientists.   While the rest of the report contains some technical language, it is generally accessible, and contains visuals to help readers understand the data.  If you are interested in gaining a better understanding of Earth’s climate and how it’s changing, we encourage you to take a look at the Climate Science Special Report to learn more.  


Peer edited by Amanda Tapia and Joanna Warren.

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Physics Through the Looking Glass

On Christmas Eve 1956, a woman caught the last train to New York in the snow to report experimental results that would alter the landscape of modern physics forever. Although members of the physics community would initially dismiss her results as nonsense, the evidence would soon become incontrovertible, launching many scientific possibilities.

C. S. Wu working in the lab.

The scientist’s name was Chien-Shiung Wu, and it took her many years of study and perseverance to make this discovery. Starting at a young age, she was quite curious about the natural world. Chien-Shiung Wu’s father, Zhongyi Wu, was an engineer who believed strongly in equal rights for women. He started the first school for girls in his region of China. Chien-Shiung Wu was one of the first girls to obtain a formal education in China. She rapidly outpaced her peers, and proceeded to an all-girls boarding school 50 miles from her home. She continued on to college in Nanjing before traveling across the globe to pursue her graduate degree at University of California, Berkeley, in the US. Not long after her arrival in California, Chien-Shiung learned of the Japanese invasion of China, which affected her family’s hometown. She would not hear from her family for eight long years. After she completed her PhD, she was considered ‘the authority‘ on nuclear fission, according to Robert Oppenheimer. Renowned physicist Enrico Fermi even consulted her for advice on how to sustain a nuclear chain reaction in the making of the atomic bomb.

For decades, physicists had assumed that, there was no way to differentiate left from right according to quantum mechanics. Quantum mechanics is the theoretical underpinning of modern physics that successfully describes the behavior subatomic particles. The assumption that left and right were indistinguishable was known as ‘parity symmetry’. It was naturally appealing, much like symmetries that exist in art, biological organisms, or other natural phenomena, like snowflakes.

Zoomed-in image of a snowflake. When Mme Wu awaited the train that Christmas Eve, she was surrounded by snowflakes, a reminder of how symmetry is ubiquitous in the natural world. Such symmetries stood in stark contrast to the discovery she was about to announce.

Nonetheless, the idea of this symmetry was called into question at a scientific conference in 1956. Within that same year, Chien-Shiung Wu would demonstrate in her lab at NIST that parity was violated for particular types of decays. In other words, these decay processes did not look the same in a mirror. This discovery was far from Chien-Shiung Wu’s only claim to fame.

Wu made many advancements in beta decay, which is the disintegration of a neutron that results in the emission of an electron and another particle called a neutrino. It was eventually with the beta decay of the element cobalt-60 that she ran her famous parity violation experiment. Using a magnetic field and low temperatures, she was able to achieve the parity violation results that turned the world on its head.

Chien-Shiung Wu did not receive the Nobel Prize, though her two male theorist colleagues did. In spite of this oversight, she obtained recognition in other ways. She was the first female physics instructor at Princeton University and the first female president of the American Physical Society (APS). Her success can be partially attributed to her parent’s encouraging attitude towards women’s education. Fortunately, they survived the Japanese invasion during World War II, with her father engineering the famous Burma Road. C. S. Wu ushered in an entirely new era in which other assumed symmetries would be overturned, helping us to more deeply understand the state of the universe that we see today.

Peer edited by Kaylee Helfrich.

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Superbug Super Problem: The Emerging Age of Untreatable Infections

You’ve heard of MRSA. You may even have heard of XDR-TB and CRE. The rise of antibiotic-resistant infections in our communities has been both swift and alarming. But how did these once easily treated infections become the scourges of the healthcare world, and what can we do to stop them?

Antibiotic-resistant bacteria pose an alarming threat to global public health and result in higher mortality, increased medical costs, and longer hospital stays. Disease surveillance shows that infections which were once easily cured, including tuberculosis, pneumonia, gonorrhea, and blood poisoning, are becoming harder and harder to treat. According to the CDC, we are entering the “post-antibiotic era”, where bacterial infections could once again mean a death sentence because no treatment is available. Methicillin-resistant Staphylococcus aureus, or MRSA, kills more Americans every year than emphysema, HIV/AIDS, Parkinson’s disease, and homicide combined. The most serious antibiotic-resistant infections arise in healthcare settings and put particularly vulnerable populations, such as immunosuppressed and elderly patients, at risk. Of the 99,000 Americans per year who die from hospital-acquired infections, the vast majority die due to antibiotic-resistant pathogens.

Cartoon by Nick D Kim, Used by permission

Bacteria become resistant to antibiotics through their inherent biology. Using natural selection and genetic adaptation, they can acquire select genetic mutations that make the bacteria less susceptible to antimicrobial intervention. An example of this could be a bacterium acquiring a mutation that up-regulates the expression of a membrane efflux pump, which is a transport protein that removes toxic substances from the cell. If the gene encoding the transporter is up-regulated or a repressor gene is down-regulated, the pump would then be overexpressed, allowing the bacteria to pump the antibiotic back out of the cell before it can kill the organism. Bacteria can also alter the active sites of antibacterial targets, decreasing the rate with which these drugs can effectively kill the bacteria and requiring higher and higher doses for efficacy. Much of the research on antibiotic resistance is dedicated to better understanding these mutations and developing new and better therapies that can overcome existing resistance mechanisms.


While bacteria naturally acquire mutations in their genome that allow them to evolve and survive, the rapid rise of antibiotic resistance in the last few decades has been accelerated by human actions. Antibiotic drugs are overprescribed, used incorrectly, and applied in the wrong context, which expose bacteria to more opportunities to acquire resistance mechanisms. This starts with healthcare professionals, who often prescribe and dispense antibiotics without ensuring they are required. This could include prescribing antibiotics to someone with a viral infection, such as rhinovirus, as well as prescribing a broad spectrum antibiotic without performing the appropriate  tests to confirm which bacterial species they are targeting. The blame is also on patients, not only for seeking out antibiotics as a “cure-all” when it’s not necessarily appropriate, but for poor patient adherence and inappropriate disposal. It’s absolutely imperative that patients follow the advice of a qualified healthcare professional and finish antibiotics as prescribed. If a patient stops dosing early, they may have only cleared out the antibiotic-susceptible bacteria and enabled the stronger, resistant bacteria to thrive in that void. Additionally, if a patient incorrectly disposes of leftover antibiotics, they may end up in the water supply and present new opportunities for bacteria to develop resistance.

Overuse of antibiotics in the agricultural sector also aggravates this problem, because antibiotics are often obtained without veterinary supervision and used without sufficient medical reasons in livestock, crops, and aquaculture, which can spread the drugs into the environment and food supply. These contributing factors to the rise of antibiotic resistance can be mitigated by proper prescriber and patient education and by limiting unnecessary antibiotic use. Policy makers also hold the power to control the spread of resistance by implementing surveillance of treatment failures, strengthening infection prevention, incentivizing antibiotic development in industry, and promoting proper public outreach and education.


While the pharmaceutical industry desperately needs to research and develop new antimicrobials to combat the rising number of antibiotic-resistant infections, the onus is also on every member of society to both promote appropriate use of antibiotics as well as ensure safe practices. The World Health Organization has issued guidelines that could help prevent the spread of infection and antibiotic resistance. In addition, World Antibiotic Awareness Week is November 13-19, 2017, and could be used as an opportunity to educate others about the risks associated with antibiotic resistance. These actions could significantly slow the spread and development of resistant infections and encourage the drug development industry to develop new antibiotics, vaccines, and diagnostics that can effectively treat and reduce antibiotic-resistant bacteria.

Peer edited by Sara Musetti 

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Underground Science at SNOLAB

The best models of how our world works are incomplete. Though they accurately describe much of what Mother Nature has thrown at us, models represent just the tip of the full iceberg and a deeper understanding awaits the endeavoring scientist. Peeling back the layers of the natural world is how we physicists seek a deeper understanding of the universe. This search pushes existing technology to its limits and fuels the innovation seen in modern day nuclear and particle physics experiments.

This is a map of the SNOLAB facility. It’s 2 km (~1.2 miles) underground and is the deepest clean room facility in the world!

Today, many of these experiments search for new physics beyond the Standard Model, the theory physicists have accepted to describe the behavior of particles. Some physical phenomena have proven difficult to reconcile with the Standard Model and research seeks to improve understanding of those conundrums, particularly regarding the properties of elusive particles known as neutrinos which have very little mass and no electric charge, and dark matter, a mysterious cosmic ingredient that holds the galaxies together but whose form is not known. The experiments pursuing these phenomena each take a different approach toward these same unknowns resulting in an impressive diversity of techniques geared towards the same goal.

On one side of the experimental spectrum, the Large Hadron Collider smashes together high-energy protons at a rate of one billion collisions per second. These collisions could have the potential to create dark matter particles or spawn interactions between particles that break expected laws of nature. On the other side of the spectrum, there is a complimentary set of experiments that quietly observe their environments, patiently waiting to detect rare signals of dark matter and other new physical processes outside the realm of behavior described by the Standard Model. As the signals from the new physics are expected to be rare (~1 event per year as compared to the LHC’s billion events per second), the patient experiments must be exceedingly sensitive and avoid any imposter signals, or  “background”, that would mimic or obscure the true signal.

The quest to decrease background interference has pushed experiments underground to cleanroom laboratories setup in mine caverns. While cleanrooms reduce the chances of unwanted radioactive isotopes, like radon-222, wandering into one’s experiment,  mines provide a mile-thick shield from interference that would be present at the surface of Earth: particles called cosmic rays constantly pepper the Earth’s surface, but very few of them survive the long journey to an underground lab.

Figure reproduced with permission from Michel Sorel from La Rivista del Nuovo Cimento, 02/2012, Volume 35, Issue 2, “The search for neutrinoless double beta decay”, J. J. Gómez-Cadenas, J. Martin-Albo, M. Mezzetto, F. Monrabal, M. Sorel, all rights reserved, with kind permission of Società Italiana di Fisica.

The rate at which muons, a cosmic ray particle, pass through underground labs decreases with the depth of the lab. At the SNOLAB facility, shown in the lower right, approximately one muon passes through a square centimeter of the lab every 100 years.

The form and function of modern underground experiments emerged from the collective insights and discoveries of the scientific community studying rare physical processes. As in any field of science, this community has progressed through decades of experimentation with results being communicated, critiqued, and validated. Scientific conferences have played an essential role in this process by bringing the community together to take stock of progress and share new ideas. The recent conference on Topics in Astroparticle and Underground Physics (TAUP) was a forum for scientists working to detect dark matter and study the properties of neutrinos. Suitably, the conference was held in the historic mining town of Sudbury, Ontario, home to the Creighton Mine, at the bottom of which lies SNOLAB, a world-class underground physics laboratory which notably housed the 2015 Nobel Prize winning SNO experiment. SNO, along with the Super-Kamiokande experiment in Japan’s Kamioka mine, was awarded “for the discovery of neutrino oscillations, which shows that neutrinos have mass.”

There is a natural excitement upon entering an active nickel mine, donning a set of coveralls, and catching a cage ride down into the depths; this was our entrance into the Creighton Mine during the TAUP conference. After descending an ear-popping 6800 feet in four minutes, we stepped out of the cage into tunnels— known as drifts— of raw rock. From there, we followed the path taken everyday by SNOLAB scientists, walking approximately one kilometer through the drifts to the SNOLAB campus. At SNOLAB, we prepared to enter the clean laboratory space by removing our coveralls, showering, and donning cleansuits. Inside, the rock walls are finished over with concrete and epoxy paint and we walked through well-lit hallways to a number of experiments which occupy impressively large caverns, some ~100 feet high.

Photo credit: Tom Gilliss

Physicists visiting SNOLAB get a close-up view of the DEAP-3600 and MiniClean dark matter experiments. Shown here are large tanks of water that shield sensitive liquid argon detectors located within.

Our tour of SNOLAB included visits to several dark matter experiments, including DEAP-3600 and MiniClean, which attempt to catch the faint glimmer of light produced by the potential interaction of dark matter particles with liquid argon. A stop by PICO-60 educated visitors on another captivating experiment, which monitors a volume of a super-heated chemical fluid for bubbles that would indicate the interaction of a dark matter particle and a nucleus. The tour also included the SNO+ experiment, offering glimpses of the search for a rare nuclear transformation of the isotope tellurium-130; because this transformation depends on the nature of neutrinos, its observation would further our understanding of these particles.

SNOLAB is also home to underground experiments from other fields. The HALO experiment, for instance, monitors the galaxy for supernovae by capturing neutrinos that are emitted by stellar explosions; neutrinos may provide the first warnings of supernovae as they are able to escape the confines of a dying star prior to any other species of particle. Additionally, the REPAIR experiment studies the DNA of fish kept underground, away from the natural levels of radiation experienced by all life on the surface of Earth.

The search for rare signals from new physical phenomena pushed physicists far underground and required the development of new technologies that have been adapted by other scientific disciplines. The SNOLAB facility, in particular, has played a key role in helping physics revise its best model of the universe, and it can be expected that similar underground facilities around the world will continue to help scientists of many stripes reveal new facets of the natural world.

Peer edited by JoEllen McBride and Tamara Vital.

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Frog Slime: The Secret to Kicking that Awful Flu

Frog slime, although gross, might help combat some strains of the influenza virus.

Got the flu? Time to start looking for your frog prince.

Researchers at Emory University have identified a substance that kills influenza, the virus that causes seasonal flu. The influenza-killing substance, called urumin, is produced on the skin of the South Indian frog and stops influenza virus growth by causing the virus to burst open-think of smashing an egg with a hammer!

Researchers think urumin disrupts a structure on the outside of the virus. Influenza, like an egg, has an outer shell that protects the contents of the virus- the “yolk”- which the virus uses to grow and replicate. Unlike an egg, the outer shell of influenza is not smooth. Instead, it contains small spikes. Urumin sticks to these influenza spikes, interfering with their function and causing the virus to burst open.

The influenza virus uses the spikes to stick to human cells and cause infection. Two types of spikes are found on each influenza virus, H and N. There are multiple types of H’s and N’s, and each virus picks one H and one N to “wear” on its outer shell, similar to the way we choose a pair of pants and shirt to wear every day.

Cartoon of Influenza. The outside is covered in spikes, H in light blue and N in dark blue.  The coils in the center contain the genetic information or “yolk” that causes the virus to replicate.  From: Doug Jordan.


Surprisingly, urumin is only effective against viruses containing the H spike type, H1. This is because urumin can only stick to H1 spikes, not to N spikes or to other types of H spikes. H1 is one of only 3 types of H spikes known to infect humans. Shockingly, H1 viruses are responsible for some of the worst flu outbreaks in history such as the 1918 Spanish flu pandemic that caused 50 million deaths and, more recently, the swine flu pandemic of 2009.

Destroying influenza in a lab environment is great, but what about in a living animal? In the same study, urumin treatment resulted in a 250% increase in mouse survival after influenza infection. Urumin treatment also decreased disease severity by lessening weight loss and decreasing the amount of virus in the lungs.

Although these mouse experiments are promising, it is important to point out that the mice were given urumin 5 minutes before they were infected with influenza and also received urumin everyday for the rest of the infection.  Because most of us do not know the exact moment we are exposed to influenza virus – the grocery store? the breakroom? the gym? – it is difficult to treat someone at the moment they are infected with influenza. Thus, more research is needed to look at the effectiveness of urumin when it is given days after infection, which is the typical time that an infected person might visit their doctor.  

With more research, urumin could be the promising new influenza drug researchers have been looking for, to potentially reduce influenza-associated deaths and complications.

Peer edited by Kaylee Helfrich

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Fossils That Slumber in the Mountains and the Mud

Over 200 million years ago, a reptile, 11 feet long and 1500 pounds, was prowling about, likely feeling very pleased with himself. Not only did he have four crunchy creatures starting to digest in his stomach, but he had bitten another weakling in the neck and then crushed it under his left knee. Just at this moment of triumph, the reptile got stuck in the mud of ancient Jordan Lake, and slowly drowned.

Around the same time, by the seaside of what would one day become Italy, the forerunners to today’s oyster were nestling on the sea floor.

41 years ago, in 1976, Dr. Joe Carter obtained his PhD from Yale University and then drove down with his wife to start a new job at Chapel Hill’s geology department. He came as a sleuth for fossils. Ancient oysters, clams, mollusks, bivalves – Dr. Carter wanted to learn as much about them as he could.

credit: Mejs Hasan

Dr. Carter and one of his fossil replicas

For most of us, shells are just the violet-tinted, half-moon shaped spectacles that nip our feet at the beach.

But for Dr. Carter, these bivalves – and especially their fossils resurrected millions of years after they lived – are clues into evolutionary history.

In 1980, Dr. Carter took a trip to the mountains of northeastern Italy. There, he found an 80-year-old man who had been collecting Triassic fossils for decades – bivalves that lived 200 to 250 million years ago. The prospect of so many fossils was like coming upon a casket of jewels for Dr. Carter. The Italian man gave him a generous sampling of his fossil collection, and Dr. Carter fell to examining them.

“Well, this looks like an oyster,” Dr. Carter speculated, as he dwelt upon one of his fossils. Or was it? Oyster fossils dated back in time for 200 million years, beyond which they disappeared into the guarded slumber of the unwritten past. Scientists had assumed this marked the juncture at which oysters evolved, and as they cast about for a suitable ancestor, they decided upon scallops: both oysters and scallops have similar, non-pearly shells.

But perhaps the little Italian oyster told a whole new story. To investigate, Dr. Carter participated in a blatant case of disturbing the peace of the deceased. He took his Italian bivalve, sharpened his knife, and embarked on a long-delayed autopsy.

He dissected the defenseless fossil into impossibly tiny 150 micrometer slices. He examined each slice carefully under a microscope, then enlarged them on plastic drafting paper. Then, he had a “eureka” moment.

Today’s oysters are almost all calcite and non-pearly. But Dr. Carter’s ancient Triassic oyster had only a hint of calcite and it consisted mostly of mother-of-pearl. Could the mother-of-pearl oyster indicate that oysters evolved from “pearl oysters”, rather than from scallops?

credit: Mejs Hasan

Momentos from a long career

It was time to see if DNA could confirm the hint provided by the fossil record, a task given to Dr. Carter’s student, Kateri Hoekstra. She performed one of the first DNA analyses of living bivalves ever to focus on their evolutionary relationships. Just as the fossil record predicted, the DNA confirmed that the oyster from the Italian mountains, dug up after its rest of 221 million years, was a closer relative of pearl oysters than scallops.

Dr. Carter sent a letter to many natural history museums in Italy, asking them to find more of the mother-of-pearl oyster. But no one ever did. Still, Dr. Carter had fine pictures and drawings of the single known fossil. People started citing the fossil as UNC-13497b.

Such a clunky name would never do for the only mother-of-pearl oyster in the world, even if it did honor our great university. Dr. Carter finally christened it Nacrolopha carolae: Nacrolopha after the nacre (mother-of-pearl) in the Lopha-like oyster, and carolae after his wife, Carol Elizabeth.

This is the sweet side of invertebrate paleontology: a fine day in the Italian mountains, mother-of-pearl oysters, and suffusing the faint echoes of history with the name of your loved one.

But not everyone wants to give fossils their due attention.

The fossil record isn’t always perfect. For example, jellyfish rarely even leave fossils. For snails, the fossil record is misleading due to convergent evolution. The same features evolved in so many different snails that it’s hard to put things in order. You see the same shapes come up again and again.

As a result, many biologists have decided to send the fossil record packing. Since it doesn’t enlighten relationships for all groups of species, the idea that it might provide clues for a few is uncharted territory.

On the other side of the line-up, you have a handful of scientists, Dr. Carter, his former students, and his research colleagues among them. They are trying to convince the biologists that for some groups of species – especially bivalves – the fossil record is actually crucial.

It’s an uphill battle because, as Dr. Carter explains, the biologists have all the money. They are awash with government funds through the “Tree of Life” project that puts primary emphasis on DNA linkages between species.

credits: Mejs Hasan

Dr. Carter working in his lab.

Dr. Carter recognizes that DNA is a necessary tool. After all, it was Kateri’s DNA analysis that confirmed the origination of Nacrolopha carolae and modern oysters from pearl oysters. But it’s not the whole story. For example, DNA tells us that our closest relatives are the chimps. But that does not mean we evolved from them, or them from us! Fossils are the missing key that can shed light on the extinct creatures who filled in the evolutionary gaps.

Dr. Carter, along with David Campbell, his former student, now a professor at Gardner-Webb University, published a paper where they described how DNA and the fossil record can be used in symphony. Unfortunately, as Dr. Carter explains, “lots of people thought it was baloney.”

That reception is not stopping Dr. Carter. He and David Campbell are trying to publish a series of papers with examples of how DNA can give faulty evidence that the fossil record can correct. As Dr. Carter says, it will be interesting to see what the opposition says at that point.

Opposition aside, there’s one set of fossils that dazzles everyone – those of dinosaurs. Dr. Carter’s one foray into reptilian fossils happened by accident. Two of his students were studying a Durham quarry in 1994, when they came across the ankle bones of “a weird new guy”. It was the same unfortunate creature that, having filled his stomach with four prey, sank into a mudhole of ancient Jordan Lake and drowned just at its very moment of triumph. Digging it up, Dr. Carter and his students found hundreds of bones. Once cleaned and reassembled, it turned out to be a reptile shaped very much like a dinosaur, but not quite.

Dinosaurs roamed about on tiptoe, but this reptile’s foot walked on both toes and heels, like humans do. It was the best-preserved skeleton of this group of reptiles ever found. Dr. Carter toured museums in Europe and the US to make sure the reptile had not been named before.

Just thereafter, Karin Peyer walked into Dr. Carter’s office. She had an undergraduate degree in paleontology, a husband starting graduate school at UNC, and time on her hands. She asked: do you need any help?

“Boy, did you come at the right time!” Dr. Carter greeted her. Karin worked with Dr. Carter and experts from the Smithsonian Institution to formally describe and name the find.

They called it Postosuchus alisonae – alisonae a tribute to a friend of Dr. Carter’s who was dying of cancer at that time.


It was December 2015. In Dr. Carter’s large dim lab, filmy sheets of plastic drafting paper were ruffling in a soft breeze from the open window looking out on a hillside over Columbia Street. Sickle-shaped knives were stacked here and there, beside replicas of treasure from King Tut’s tomb. In between sectioning and sketching an ancient bivalve called Modiolopsis, Dr. Carter was packing.

credits: Mejs Hasan

Dr. Carter at his retirement party

He was retiring after 39 years. In practice, that merely means that Dr. Carter can now avoid going to faculty meetings. Otherwise, he can still serve on graduate student committees; he is coordinating the revisions of bivalves in the Treatise of Invertebrate Paleontology. He still has fossils to section and examine, and biologists to convince of the worth of the fossil record.

The only difference is, when Dr. Carter began his professorial work, it was just him and his wife, a young daughter and a baby boy. Now his daughter is 45 years old and his son is 39, and they both have their own families that Dr. Carter will be spending a lot of time with. It’s amazing what changes four decades can bring. But perhaps it’s easier to be philosophical and surrender to what’s ahead when you hold in your hands an oyster that lived 221 million years ago.

Peer edited by Lindsay Walton and Alison Earley.

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