Ancient, massive asteroid impact could explain Martian geological mysteries

Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft.

The origin and nature of Mars is mysterious. It has geologically distinct hemispheres, with smooth lowlands in the north and cratered, high-elevation terrain in the south. The red planet also has two small oddly-shaped oblong moons and a composition that sets it apart from that of the Earth.

New research by University of Colorado Boulder professor Stephen Mojzsis outlines a likely cause for these mysterious features of Mars: a colossal impact with a large asteroid early in the planet's history. This asteroid -- about the size of Ceres, one of the largest asteroids in the Solar System -- smashed into Mars, ripped off a chunk of the northern hemisphere and left behind a legacy of metallic elements in the planet's interior. The crash also created a ring of rocky debris around Mars that may have later clumped together to form its moons, Phobos and Deimos.

The study appeared online in the journal Geophysical Research Letters, a publication of the American Geophysical Union, in June.

"We showed in this paper -- that from dynamics and from geochemistry -- that we could explain these three unique features of Mars," said Mojzsis, a professor in CU Boulder's Department of Geological Sciences. "This solution is elegant, in the sense that it solves three interesting and outstanding problems about how Mars came to be."

Astronomers have long wondered about these features. Over 30 years ago, scientists proposed a large asteroid impact to explain the disparate elevations of Mars' northern and southern hemispheres; the theory became known as the "single impact hypothesis." Other scientists have suggested that erosion, plate tectonics or ancient oceans could have sculpted the distinct landscapes. Support for the single impact hypothesis has grown in recent years, supported by computer simulations of giant impacts.

Mojzsis thought that by studying Mars' metallic element inventory, he might be able to better understand its mysteries. He teamed up with Ramon Brasser, an astronomer at the Earth-Life Science Institute at the Tokyo Institute of Technology in Japan, to dig in.

The team studied samples from Martian meteorites and realized that an overabundance of rare metals -- such as platinum, osmium and iridium -- in the planet's mantle required an explanation. Such elements are normally captured in the metallic cores of rocky worlds, and their existence hinted that Mars had been pelted by asteroids throughout its early history. By modeling how a large object such as an asteroid would have left behind such elements, Mojzsis and Brasser explored the likelihood that a colossal impact could account for this metal inventory.

The two scientists first estimated the amount of these elements from Martian meteorites, and deduced that the metals account for about 0.8 percent of Mars' mass. Then, they used impact simulations with different-sized asteroids striking Mars to see which size asteroid accumulated the metals at the rate they expected in the early solar system.

Based on their analysis, Mars' metals are best explained by a massive meteorite collision about 4.43 billion years ago, followed by a long history of smaller impacts. In their computer simulations, an impact by an asteroid at least 1,200 kilometers (745 miles) across was needed to deposit enough of the elements. An impact of this size also could have wildly changed the crust of Mars, creating its distinctive hemispheres.

In fact, Mojzsis said, the crust of the northern hemisphere appears to be somewhat younger than the ancient southern highlands, which would agree with their findings.

"The surprising part is how well it fit into our understanding of the dynamics of planet formation," said Mojzsis, referring to the theoretical impact. "Such a large impact event elegantly fits in to what we understand from that formative time."

Such an impact would also be expected to have generated a ring of material around Mars that later coalesced into Phobos and Deimos; this explains in part why those moons are made of a mix of native and non-Martian material.

In the future, Mojzsis will use CU Boulder's collection of Martian meteorites to further understand Mars' mineralogy and what it can tell us about a possible asteroid impact. Such an impact should have initially created patchy clumps of asteroid material and native Martian rock. Over time, the two material reservoirs became mixed. By looking at meteorites of different ages, Mojzsis can see if there's further evidence for this mixing pattern and, therefore, potentially provide further support for a primordial collision.

Read more at Science Daily

Human-made aerosols identified as driver in shifting global rainfall patterns

Spatial distribution of the annual-mean precipitation averaged from 1979-2008.

In a new study, scientists found that aerosol particles released into the atmosphere from the burning of fossil fuels are a primary driver of changes in rainfall patterns across the globe.

The results of the climate system-model simulations conducted by researchers Brian Soden and Eui-Seok Chung from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science revealed that changes in clouds, as a result of their interaction with these human-made aerosols in the atmosphere, are driving large-scale shifts in rainfall and temperature on Earth.

A southward shift of the tropical rain belt is thought to be the leading cause of the severe drought conditions experienced in large portions of Africa and South America during the second half of the 20th century, which have caused significant impacts to local communities and water availability in these regions.

Using multiple climate model projections, the researchers measured the effects human-made aerosols have had on rainfall changes in the 20th and 21st centuries to discover that when only greenhouse gases or natural climate forces are considered, climate models are not able to capture the southward shift of the tropical rain belt. The analysis suggests that human-made aerosols are the primary driver of the observed southward shift in rainfall patters throughout the latter half of the 20th century.

"Our analysis showed that interactions between aerosol particles and clouds have caused large-scale shifts in precipitation during the latter half of the 20th century, and will play a key role in regulating future shifts in tropical rainfall patterns," said UM Rosenstiel School atmospheric scientist Chung, the lead author of the study.

Changes in the radiative properties of clouds from the increase of these human-made particles in the atmosphere is resulting in large-scale changes in atmospheric circulation that drive regional climate and rainfall, say the researchers.

"Human-induced changes in rainfall can have substantial implications for society and the environment by affecting the availability of water," said Soden, a UM Rosenstiel School atmospheric sciences professor and the senior author of the study. "Our work helps to understand the mechanisms that drive large-scale shifts in precipitation to better predict how the climate will change in the future."

The models the researchers used also found that the largest shift in rainfall patterns will occur over the tropics rather than in the mid-latitude northern hemisphere, the greatest source region of these human-made industrial aerosols.

Understanding these aerosol-cloud interactions are necessary to better model future changes in tropical rainfall worldwide.

Read more at Science Daily

Why Tyrannosaurus was a slow runner and why the largest are not always the fastest

There is a parabola-like relationship between the body mass of animals and the maximum speed they can reach. For the first time, researchers are able to describe how this comes about, thanks to a simple mathematical model.

No other animal on land is faster than a cheetah -- the elephant is indeed larger, but slower. For small to medium-sized animals, larger also means faster, but for really large animals, when it comes to speed, everything goes downhill again. For the first time, it is now possible to describe how this parabola-like relationship between body size and speed comes about. A research team under the direction of the German Centre for Integrative Biodiversity Research (iDiv) and the Friedrich Schiller University Jena (Germany) have managed to do so thanks to a new mathematical model, and also published their findings in the journal Nature Ecology and Evolution.

A beetle is slower than a mouse, which is slower than a rabbit, which is slower than a cheetah... which is slower than an elephant? No! No other animal on land is faster than a cheetah -- the elephant is indeed larger, but slower. For small to medium-sized animals, larger also means faster, but for really large animals, when it comes to speed, everything goes downhill again. For the first time, it is now possible to describe how this parabola-like relationship between body size and speed comes about.

The model is amazingly simple: The only information that it must be 'fed' with is the weight of a particular animal as well as the medium it moves in, so either land, air or water. On this basis alone, it calculates the maximum speed that an animal can reach with almost 90% accuracy. "The best feature of our model is that it is universally applicable," says the lead author of the study, Myriam Hirt of the iDiv research centre and the University of Jena. "It can be performed for all body sizes of animals, from mites to blue whales, with all means of locomotion, from running and swimming to flying, and can be applied in all habitats." Moreover, the model is by no means limited to animal species that currently exist, but can be applied equally well to extinct species.

Tyrannosaurus reached a speed of only 17 miles/hour

"To test whether we can use our model to calculate the maximum speed of animals that are already extinct, we have applied it to dinosaur species, whose speed has up to now been simulated using highly complex biomechanical processes," explains Hirt. The result is that the simple model delivered results for Triceratops, Tyrannosaurus, Brachiosaurus and others that matched those from complex simulations -- and were not exactly record-breaking for Tyrannosaurus, who reached a speed of only 27 km/h (17 mi/h). "This means that in future, our model will enable us to estimate, in a very simple way, how fast other extinct animals were able to run," says the scientist.

Read more at Science Daily

You're not yourself when you're sleepy

Poor sleep is associated with a particularly serious sign of depression, suggests new research.

More than a third of Americans don't get enough sleep, and growing evidence suggests it's not only taking a toll on their physical health through heart disease, diabetes, stroke, and/or other conditions, but hurting their mental health as well.

According to a recent study led by Postdoctoral FellowIvan Vargas, PhD, in the journal Cognitive Therapy and Research, those who are sleep deprived lose some of their ability to be positive-minded people. That may not sound serious, but medical experts say an inability to think positively is a serious symptom of depression that could be dangerous if left unaddressed. An estimated 16.1 million adults experienced a major depressive episode in 2014.

"In general, we have a tendency to notice positive stimuli in our environment," said Vargas. "We tend to focus on positive things more than anything else, but now we're seeing that sleep deprivation may reverse that bias."

In their study, Vargas and his team took 40 healthy adults, and randomized them to either 28 consecutive hours awake, or a full eight hours of sleep. All participants participated in a computer test measuring their accuracy and response time at identifying happy, sad and neutral faces to assess how they pay attention to positive or negative information.

The team found that those who were acutely sleep deprived were less likely to focus on the happy faces. They didn't necessarily focus more on the negative, but were less likely to focus on the positive. The study may have implications for those experiencing depression and/or anxiety.

There are many symptoms of depression -- including feeling sad and no longer being able to enjoy things you typically would, but poor sleep is associated with a particularly serious sign of the condition.

"Depression is typically characterized as the tendency to think and feel more negatively or sad, but more than that, depression is associated with feeling less positive, less able to feel happy," Vargas says, "Similarly, if you don't get enough sleep, it reduces your ability to attend to positive things, which over time may confer risk for depression."

Interestingly enough, in the present study, those with a history of insomnia symptoms were less sensitive to the effects of the sleep loss. The authors believe this might be because those with a history of insomnia symptoms have more experience being in sleep-deprived conditions and have developed coping methods to modulate the effect of sleep loss.

Vargas and colleagues recently presented a related study at SLEEP 2017, the 31st Annual Meeting of the Associated Professional Sleep Societies LLC, on the association of insomnia and suicide, finding that people who suffer from insomnia are three times more likely to report thoughts of suicide and death during the past 30 days than those without the condition.

The study comes amid a growing body of knowledge associating sleep disorders and depression. For example, ongoing research presented this year at SLEEP 2017 from a multi-center NIH-sponsored "Treatment of Insomnia and Depression" study (abstract 0335 here) suggests that cognitive-behavioral therapy for insomnia (CBT-I) may help achieve depression remission in those suffering from both depression and insomnia who sleep at least 7 hours each night. (A clinical practice guideline published in 2016 in Annals of Internal Medicine recommends CBT-I (not sleep medications) as the initial treatment for chronic insomnia.

Read more at Science Daily

Oil impairs ability of coral reef fish to find homes and evade predators

This is a damselfish of the Chromis species.

Just as one too many cocktails can lead a person to make bad choices, a few drops of oil can cause coral reef fish to make poor decisions, according to a paper published in Nature Ecology & Evolution. A team of fisheries biologists led by Jacob Johansen and Andrew Esbaugh of The University of Texas Marine Science Institute have discovered that oil impacts the higher-order thinking of coral reef fish in a way that could prove dangerous for them -- and for the coral reefs where they make their home.

Examining six different species of coral reef fish, Johansen and the team found that exposure to oil consistently affected behavior in ways that put the fish at risk.

During several weeks when coral reef fish go through their juvenile stages of development, they are especially vulnerable. Even in healthy populations of reef fish, typically less than 10 percent of embryos and larvae reach adulthood. Those who survive must learn to identify friend from foe and adopt protective behaviors, such as traveling in groups, minimizing movement in open waters and swimming away quickly from danger.

In experiments, the scientists found that juvenile fish exposed to oil struggled on all these counts.

"In several different experiments, the fish exposed to oil exhibited very risky behavior, even in the presence of a predator," said Esbaugh, an assistant professor of marine science.

The scientists also found that oil exposure negatively affected the fishes' growth, survival and settlement behaviors (their ability to find a suitable habitat).

Oil concentrations are found in oceans worldwide, but until now little has been known about the impact of oil exposure on coral reef fish. Earlier research that explored how oil affects the physiology of fishes has demonstrated developmental heart deformities and associated cardiac functions, but this is the first study to demonstrate that oil exposure affects behavior in a way that increases predation and reduces settlement success.

The finding could be bad news for reefs, as well, since many coral reefs depend on fish to remove algae that can restrict their growth and development. Coral reef ecosystems are the oceans' most diverse ecosystems -- and the most threatened. Hundreds of millions of people depend on coral reefs and their fish for income or food, but widespread coral bleaching and overfishing threaten this way of life. The new study indicates that limiting oil-based industrial activities near reefs may be critical for reef preservation.

"Over the past 35 years, almost one-fifth of the world's coral reefs have been lost and half of what's remaining is either expected to disappear or be under severe threat in the next few decades," Johansen, the lead researcher, reflected. "Still, many governments continue to allow industrial activities, including oil drilling and exploration, in sensitive reef habitats. If a spill were to occur, this study suggests there could be major consequences for the fish, for coral reefs and for people working in fisheries and tourism."

"We used oil concentrations that are already present in many industrialized regions worldwide -- concentrations that ranged from two to five parts per billion, the equivalent of a couple of drops in a swimming pool," Johansen said.

Read more at Science Daily

New species of dinosaur named after Canadian icon

This is a life recreation of Albertavenator curriei.

Scientists from the Royal Ontario Museum (ROM) and the Philip J Currie Dinosaur Museum have identified and named a new species of dinosaur in honour of renowned Canadian palaeontologist Dr. Philip J. Currie. Albertavenator curriei, meaning "Currie's Alberta hunter." It stalked Alberta, Canada, about 71 million years ago in what is now the famous Red Deer River Valley. The find recognizes Currie for his decades of work on predatory dinosaurs of Alberta. Research on the new species is published July 17 in the Canadian Journal of Earth Sciences.

Palaeontologists initially thought that the bones of Albertavenator belonged to its close relative Troodon, which lived around 76-million-years-ago -- five million years before Albertavenator. Both dinosaurs walked on two legs, were covered in feathers, and were about the size of a person. New comparisons of bones forming the top of the head reveal that Albertavenator had a distinctively shorter and more robust skull than Troodon, its famously brainy relative.

"The delicate bones of these small feathered dinosaurs are very rare. We were lucky to have a critical piece of the skull that allowed us to distinguish Albertaventaor as a new species." said Dr. David Evans, Temerty Chair and Senior Curator of Vertebrate Palaeontology at the Royal Ontario Museum, and leader of the project. "We hope to find a more complete skeleton of Albertavenator in the future, as this would tell us so much more about this fascinating animal."

Identifying new species from fragmentary fossils is a challenge. Complicating matters of this new find are the hundreds of isolated teeth that have been found in Alberta and previously attributed to Troodon. Teeth from a jaw that likely pertains to Albertavenator appears very similar to the teeth of Troodon, making them unusable for distinguishing between the two species.

"This discovery really highlights the importance of finding and examining skeletal material from these rare dinosaurs," concluded Derek Larson, co-author on the study and Assistant Curator of the Philip J. Currie Dinosaur Museum."

The identification of a new species of troodontid in the Late Cretaceous of North America indicates that small dinosaur diversity in the latest Cretaceous of North America is likely underestimated due to the difficulty of identifying species from fragmentary fossils.

"It was only through our detailed anatomical and statistical comparisons of the skull bones that we were able to distinguish between Albertavenator and Troodon," said Thomas Cullen, a Ph.D. student of Evans at the University of Toronto and co-author of the study.

The bones of Albertavenator were found in the badlands surrounding the Royal Tyrrell Museum, which Dr. Currie played a key role in establishing in the early 1980s. The rocks around the museum are the same age as some of the most fossiliferous rocks in the area of the newly erected Philip J. Currie Museum, also named in Dr. Currie's honour. Although Dr. Currie has also had a several dinosaurs named after him, this is only the second one from Alberta, where he has made his biggest impact.

Read more at Science Daily

Is this Gulf of Mexico tubeworm the longest living animal in the world?

The tubeworm species Escarpia laminata.

Large tubeworms living in the cold depths of the Gulf of Mexico may be among the longest living animals in the world. This is revealed in a study in Springer's journal The Science of Nature. According to lead author Alanna Durkin of Temple University in the US, members of the tubeworm species Escarpia laminata live around 100 to 200 years, while the longevity of some even stretches to the three century mark.

Escarpia laminata is a type of tubeworm that lives in cold seeps found between 1000 meters and 3300 meters deep on the ocean floor of the Gulf of Mexico. Hydrogen sulphide, methane and other hydrocarbon-rich fluids seep out of these vents.

Because so little is known about this species and its life history, Durkin and her colleagues set out to estimate its lifespan. The team also wanted to find out if it is as long-lived as other types of tubeworms living in cold seeps in shallower waters, such as Lamellibrachia luymesi and Seepiophila jonesi.

They collected and marked 356 tubeworms at different locations in the Gulf of Mexico and measured how much these grew over the course of one year. This method for modelling annual growth was first developed to calculate the age of Lamellibrachia luymesi, which is estimated to live up to 250 years. The average individual growth model was then extended to also include death rates and recruitment rates to construct a population-wide simulation. In the process, the age and growth rates of the individual tubeworms collected could be estimated.

The individual and population level approaches indicate that larger Escarpia laminata individuals live longer than 250 years. An Escarpia laminata tubeworm fifty centimeters in length is predicted to be 202 years old. This species therefore lives much longer than its relatives, Lamellibrachia luymesi and Seepiophila jonesi. This lifespan is also far beyond estimates based on universal scaling laws for Escarpia laminata's body size and ambient temperature.

According to Durkin, Escarpia laminata's extremely low death rate has helped it evolve a very long lifespan. The results support longevity theory, which states that in the absence of any external threats natural selection will select for individuals that show signs of ageing more slowly and can reproduce continually into their old age.

"At more than 250 years old, Escarpia laminata achieves a lifespan that exceeds other longevity records," says Durkin. "Given the uncertainty associated with estimating the ages of the longest individuals, there may be large Escarpia laminata tubeworms alive in nature that live even longer."

Read more at Science Daily

Climate Change Could Cause More Flight Delays at the World's Busiest Airports

Imagine boarding a summertime flight at LaGuardia Airport in New York City, only to be told that the airline needs a dozen or so passengers to take a later flight because it’s too hot outside for the plane to take off fully loaded.

That could become a common scenario at 19 major airports worldwide as extreme heat caused by global warming disrupts an increasing number of flights departing during the hottest times of day, according to a new Columbia University study.

If human greenhouse gas emissions are not reduced, global average temperatures are expected to rise by more than 4°C (7.2°F) by 2100. But high temperatures at the world’s busiest airports could rise even more — by up to 8°C (14.4°F), leading to more days each year that are hotter than average, especially at airports in the tropics, according to the study, published Thursday in the journal Climatic Change.

By 2065, LaGuardia Airport could see about 25 days each year that will be hotter than today’s average yearly high temperature, up from fewer than 10 days in 2025.

Extreme heat disrupted flights in Phoenix in June when American Airlines cancelled 50 flights aboard small commuter jets as temperatures soared above 120°F. Such summertime temperatures are likely to become more frequent as the climate changes. Air is less dense in extreme heat, preventing an airplane's wings from generating enough lift to take off unless the plane sheds weight.

“Higher temperatures are going to mean more people having to be removed from flights, more delays on the ground,” said study co-author Radley Horton, a climate scientist at Columbia University.

The amount of weight and number of passengers a flight would have to shed depend on the type of aircraft and the airport’s altitude and runway length. LaGuardia could be affected by the heat more than New York’s Kennedy International Airport because its runways are nearly half the length of Kennedy’s longest runway.

Between 10 and 30 percent of annual flights departing at the hottest hours of the day from 19 major airports will have to fly with weight restrictions, the study says. On average, flights will have to cut their weight by up to 4 percent in order to take off on the hottest days after 2050.

Some larger planes, especially those that fly long-haul international flights to mid-sized or small airports, could be affected more than smaller planes because they weigh more. However, the largest plane flying today, the double-decker Airbus A380, may not be affected as much by the heat because it can only fly to airports with the longest runways.

The study suggests that one way airlines could avoid heat-related flight disruptions is to schedule flights at night or in the morning when the air is cooler. But airplanes and airports may need to be designed differently in the future in order to deal with the heat as the globe warms.

“As it gets warmer, air expands,” said Lou McNally, an assistant professor of applied aviation sciences at Embry-Riddle Aeronautical University in Daytona Beach, Fla., who is unaffiliated with the study. “That means you need more of everything in order to get enough air molecules onto the wing and fly. It means more thrust — bigger or more engines — and more runway length for takeoff, or larger wings, or all of the above. And also more runway length and better braking because of higher landing speeds at the other end.”

Read more at Seeker

New limits to functional portion of human genome reported

The functional portion of the human genome probably falls between 10 percent and 15 percent, with an upper limit of 25 percent, suggests new research.

An evolutionary biologist at the University of Houston has published new calculations that indicate no more than 25 percent of the human genome is functional. That is in stark contrast to suggestions by scientists with the ENCODE project that as much as 80 percent of the genome is functional.

In work published online in Genome Biology and Evolution, Dan Graur reports the functional portion of the human genome probably falls between 10 percent and 15 percent, with an upper limit of 25 percent. The rest is so-called junk DNA, or useless but harmless DNA.

Graur, John and Rebecca Moores Professor of Biology and Biochemistry at UH, took a deceptively simple approach to determining how much of the genome is functional, using the deleterious mutation rate - that is, the rate at which harmful mutations occur - and the replacement fertility rate.

Both genome size and the rate of deleterious mutations in functional parts of the genome have previously been determined, and historical data documents human population levels. With that information, Graur developed a model to calculate the decrease in reproductive success induced by harmful mutations, known as the "mutational load," in relation to the portion of the genome that is functional.

The functional portion of the genome is described as that which has a selected-effect function, that is, a function that arose through and is maintained by natural selection. Protein-coding genes, RNA-specifying genes and DNA receptors are examples of selected-effect functions. In his model, only functional portions of the genome can be damaged by deleterious mutations; mutations in nonfunctional portions are neutral since functionless parts can be neither damaged nor improved.

Because of deleterious mutations, each couple in each generation must produce slightly more children than two to maintain a constant population size. Over the past 200,000 years, replacement-level fertility rates have ranged from 2.1 to 3.0 children per couple, he said, noting that global population remained remarkably stable until the beginning of the 19th century, when decreased mortality in newborns resulted in fertility rates exceeding replacement levels.

If 80 percent of the genome were functional, unrealistically high birth rates would be required to sustain the population even if the deleterious mutation rate were at the low end of estimates, Graur found.

"For 80 percent of the human genome to be functional, each couple in the world would have to beget on average 15 children and all but two would have to die or fail to reproduce," he wrote. "If we use the upper bound for the deleterious mutation rate (2 × 10?8 mutations per nucleotide per generation), then ... the number of children that each couple would have to have to maintain a constant population size would exceed the number of stars in the visible universe by ten orders of magnitude."

In 2012, the Encyclopedia of DNA Elements (ENCODE) announced that 80 percent of the genome had a biochemical function. Graur said this new study not only puts these claims to rest but hopefully will help to refocus the science of human genomics.

Read more at Science Daily

Fossil site shows impact of early Jurassic's low oxygen oceans

Before the low oxygen period, bivalves were larger and more numerous.

Using a combination of fossils and chemical markers, scientists have tracked how a period of globally low ocean-oxygen turned an Early Jurassic marine ecosystem into a stressed community inhabited by only a few species.

The research was led by Rowan Martindale, an assistant professor at The University of Texas at Austin Jackson School of Geosciences, and published in print in Palaeogeography, Palaeoclimatology, Palaeoeconology on July 15. The study was co-authored by Martin Aberhan, a curator at the Institute for Evolution and Biodiversity Science at the Natural History Museum in Berlin, Germany.

The study zeroes in on a recently discovered fossil site in Canada located at Ya Ha Tinda Ranch near Banff National Park in southwest Alberta. The site records fossils of organisms that lived about 183 million years ago during the Early Jurassic in a shallow sea that once covered the region.

The fossil site broadens the scientific record of the Toarcian Oceanic Anoxic Event, a period of low oxygen in shallow ocean waters which is hypothesized to be triggered by massive volcanic eruptions. The Oceanic Anoxic Event was identified at this site by the geochemical record preserved in the rocks. These geochemical data were collected in a previous research project led by Benjamin Gill and Theodore Them of Virginia Tech. The oxygen level of the surrounding environment during the Early Jurassic influences the type and amount of carbon preserved in rocks, making the geochemical record an important method for tracking an anoxic event.

"We have this beautiful geochemical record that gives us a backbone for the timing of the Oceanic Anoxic Event," said Martindale, a researcher in the Jackson School's Department of Geological Sciences. "So with that framework we can look at the benthic community, the organisms that are living on the bottom of the ocean, and ask 'how did this community respond to the anoxic event?"

The fossils show that before the anoxic event, the Ya Ha Tinda marine community was diverse, and included fish, ichthyosaurs (extinct marine reptiles that looked like dolphins), sea lilies, lobsters, clams and oysters, ammonites, and coleoids (squid-like octopods). During the anoxic event the community collapsed, restructured, and the organisms living in it shrunk. The clams that were most abundant in the community before the anoxic event were completely wiped out and replaced by different species.

The clams that survived during and after the event were much smaller than the clams from before the event, suggesting that low oxygen levels limited their growth.

The sea life recorded at Ya Ha Tinda before and during the anoxic event is similar to fossils found at European sites. Crispin Little, a senior lecturer in paleontology at The University of Leeds who was not involved with the research, said that the similarity between the sites underscores the widespread nature of the anoxic event.

"This confirms previous work suggesting that the T-OAE (anoxic event) was genuinely a global event," Little said.

However, while other sites were recovering from the anoxic event, the environment at Ya Ha Tinda continued to face stress. Even for small, hardy bivalves, life was tough.

"One of the interesting things about the recovery [at Ya Ha Tinda] is that we actually see fewer individuals at a time when we're supposed to be seeing community recovery," Martindale said.

The fossils suggest that the environment was undergoing local stresses that kept oxygen low, Martindale said. More research is needed to untangle why life at Ya Ha Tinda didn't recover at the same rate as other places.

Since the oceanic anoxic event was a side-effect of climate change, looking back at ancient marine communities could be a window into the potential impacts of ongoing and future climate change, said co-author Martin Aberhan.

Read more at Science Daily