These ā€œā€ events have happened only a handful of times and do not occur on regular cycles. Each lasts for millions of years or tens of millions of years and is followed by dramatic warming, but the details of these transitions are poorly understood.

New research from the 91±¬ĮĻ provides a more complete picture for how the last Snowball Earth ended, and suggests why it preceded a dramatic expansion of life on Earth, including the emergence of the first animals.

The recently published in Nature Communications focuses on ancient rocks known as ā€œcap carbonates,ā€ thought to have formed as the glacial ice thawed. These rocks preserve clues to Earthā€™s atmosphere and oceans about 640 million years ago, far earlier than what ice cores or tree rings can record.

ā€œCap carbonates contain information about key properties of Earth’s atmosphere and ocean, such as changing levels of carbon dioxide in the air, or the acidity of the ocean,ā€ said lead author , a 91±¬ĮĻ doctoral student in Earth and space sciences. ā€œOur theory now shows how these properties changed during and after Snowball Earth.ā€

are layered limestone or dolomite rocks that have a distinct chemical makeup and today are found in over 50 global locations, including Death Valley, Namibia, Siberia, Ireland and Australia. These rocks are thought to have formed as the Earth-encircling ice sheets melted, causing dramatic changes in atmospheric and ocean chemistry and depositing this unique type of sediment onto the ocean floor.

They are called ā€œcapsā€ because they are the caps above glacial deposits left after Snowball Earth, and ā€œcarbonatesā€ because both limestone and dolomite are carbon-containing rocks. Understanding their formation helps explain the carbon cycle during periods of dramatic climate change. The new study, which models the environmental changes, also provides hints about the evolution of life on Earth and why more complex lifeforms followed the last Snowball Earth.

ā€œLife on Earth was simple ā€” in the form of microbes, algae or other tiny aquatic organisms ā€” for over 2 billion years leading up to Snowball Earth,ā€ said senior author , a 91±¬ĮĻ professor of Earth and space sciences. ā€œIn fact, the billion years leading up to Snowball Earth are called the ā€˜boring billionā€™ because so little happened. Then two Snowball Earth events occurred. And soon after, animals appear in the fossil record.ā€

The new paper provides a framework for how the last two facts may be connected.

The study modeled chemistry and geology during three phases of Snowball Earth. First, during Snowball Earthā€™s peak, thick ice encircling the planet reflected sunlight, but some areas of open water allowed exchange between the ocean and atmosphere. Meanwhile frigid seawater continued to react with the ocean floor.

Eventually, carbon dioxide built up in the atmosphere to the point where it trapped enough solar energy to raise global temperatures and melt the ice. This let rainfall reach the Earth, and let freshwater flow into the ocean to join a layer of glacial meltwater that floated over the denser, salty ocean water. This layered ocean slowed down ocean circulation. Later, ocean churning picked up, and mixing between the atmosphere, upper ocean, and deep ocean resumed.

ā€œWe predict important changes in the environment as Earth recovered from the Snowball period, some of which affected the temperature, acidity and circulation of the ocean. Now that we know these changes, we can more confidently figure out how they affected Earthā€™s life,ā€ Thomas said.

Future research will explore how pockets of life that may have survived the tumult of the Snowball Earth and its aftermath could have evolved into the more complex lifeforms that followed soon after.

The research was funded by the National Science Foundation and NASA, in part by a NASA Astrobiology Program grant to the 91±¬ĮĻā€™s Virtual Planetary Laboratory.

For more information, contact Thomas at tbthomas@uw.edu or Catling at dcatling@uw.edu.

Charles Darwin proposed that life could have emerged in a ā€œā€ with the right cocktail of chemicals and energy. A from the 91±¬ĮĻ, published this month in Communications Earth & Environment, reports that a shallow ā€œsoda lakeā€ in western Canada shows promise for matching those requirements. The findings provide new support that life could have emerged from lakes on the early Earth, roughly 4 billion years ago.

Scientists have known that under the right conditions, the complex molecules of life can emerge spontaneously. As recently fictionalized in the blockbuster hit ā€œLessons in Chemistry,ā€ biological molecules can be coaxed to form from inorganic molecules. In fact, long after made amino acids, the building blocks of proteins, has made the building blocks of RNA. But this next step requires extremely high phosphate concentrations.

Phosphate forms the ā€œbackboneā€ of RNA and DNA and is also a key component of cell membranes. The concentrations of phosphate required to form these biomolecules in the lab are hundreds to 1 million times higher than the levels normally found in rivers, lakes or in the ocean. This has been called the ā€œphosphate problemā€ for the emergence of life ā€” a problem that soda lakes may have solved.

ā€œI think these soda lakes provide an answer to the phosphate problem,ā€ said senior author , a 91±¬ĮĻ professor of Earth and space sciences. ā€œOur answer is hopeful: This environment should occur on the early Earth, and probably on other planets, because it’s just a natural outcome of the way that planetary surfaces are made and how water chemistry works.ā€

Soda lakes get their name from having high levels of dissolved sodium and carbonate, similar to dissolved baking soda. This occurs from the reactions between water and volcanic rocks beneath. Soda lakes can also have high levels of dissolved phosphate.

Previous 91±¬ĮĻ research in 2019 found that chemical conditions for life to emerge could theoretically occur in soda lakes. The researchers combined chemical models with laboratory experiments to show that natural processes can theoretically concentrate phosphate in these lakes to levels up to 1 million times higher than in typical waters.

For the new study, the team set out to study such an environment on Earth. By coincidence, the most promising candidate was within driving distance. Tucked away at the end of a from the 1990s was the highest known natural phosphate level in the scientific literature at in inland British Columbia, Canada, about seven hoursā€™ drive from Seattle.

The lake is about 1 foot deep and has murky water with fluctuating levels. It sits on federal land at the end of a dusty dirt road on the Cariboo Plateau, in British Columbia ranching country. The shallow lake meets the requirements for a soda lake: a lake above volcanic rock (in this case, basalt) combined with a dry, windy atmosphere that evaporates incoming water to keep water levels low and concentrates dissolved compounds within the lake.

Analysis published in the new paper suggests soda lakes are a strong candidate for the emergence of life on Earth. They also could be a candidate for life on other planets.

ā€œWe studied a natural environment that should be common throughout the solar system. Volcanic rocks are prevalent on the surfaces of planets, so this same water chemistry could have occurred not just on early Earth, but also on early Mars and early Venus, if liquid water was present,ā€ said lead author , a postdoctoral researcher in Earth and space sciences at the 91±¬ĮĻ.

The 91±¬ĮĻ team visited Last Chance Lake three times from 2021 to 2022. They collected observations in early winter, when the lake was covered in ice; in early summer, when rain-fed springs and snowmelt-fed streams put water at its highest; and in late summer when the lake had almost completely dried up.

ā€œYou have this seemingly dry salt flat, but there are nooks and crannies. And between the salt and the sediment there are little pockets of water that are really high in dissolved phosphate,ā€ Haas said. ā€œWhat we wanted to understand was why and when could this happen on the ancient Earth, in order to provide a cradle for the origin of life.ā€

On all three visits the team collected samples of water, lake sediment and salt crust to understand the lakeā€™s chemistry.

In most lakes the dissolved phosphate quickly combines with calcium to form calcium phosphate, the insoluble material that makes up our tooth enamel. This removes phosphate from the water. But in Last Chance Lake, calcium combines with plentiful carbonate as well as magnesium to form dolomite, the same mineral that forms picturesque mountain ranges. This reaction was predicted by the previous modeling work and confirmed when dolomite was plentiful in Last Chance Lakeā€™s sediments. When calcium turns into dolomite and does not remain in the water, the phosphate lacks a bonding partner ā€” and so its concentration rises.

ā€œThis study adds to growing evidence that evaporative soda lakes are environments meeting the requirements for origin-of-life chemistry by accumulating key ingredients at high concentrations,ā€ Catling said.

The study also compared Last Chance Lake with Goodenough Lake, a roughly 3-foot-deep lake with clearer water and different chemistry just a two-minute walk away, to learn what makes Last Chance Lake unique. The researchers wondered why life, present in all modern lakes at some level, was not using up the phosphate in Last Chance Lake.

Goodenough Lake has mats of cyanobacteria that extract or ā€œfixā€ nitrogen gas from the air. Cyanobacteria, like all other lifeforms, also require phosphate ā€” and its growing population consumes some of that lake waterā€™s phosphate supply. But Last Chance Lake is so salty that it inhibits living things that do the energy-intensive work of fixing atmospheric nitrogen. Last Chance Lake harbors some algae but has insufficient available nitrogen to host more life, allowing phosphate to accumulate. This also makes it a better analog for a lifeless Earth.

ā€œThese new findings will help inform origin-of-life researchers who are either replicating these reactions in the lab or are looking for potentially habitable environments on other planets,ā€ Catling said.

The research was funded by the Simons Foundation. The other co-author is , a 91±¬ĮĻ graduate student in Earth and space sciences. Graduate students with the 91±¬ĮĻ Astrobiology Program also assisted with sample collection.

For more information, contact Haas at sb704989@uw.edu or Catling at dcatling@uw.edu.

The American Geophysical Union Sept. 13 that five 91±¬ĮĻ faculty members have been elected as new fellows, representing the departments of astronomy, Earth and space sciences, oceanography, global health, and environmental and occupational health sciences.

The Fellows program recognizes AGU members who have made exceptional contributions to Earth and space sciences through a breakthrough, discovery or innovation in their field. The five 91±¬ĮĻ honorees are among 54 people from around the world in the 2023 Class of Fellows. AGU, the world’s largest Earth and space sciences association, annually recognizes a select number of individuals nominated by their peers for its highest honors. Since 1962, the AGU Union Fellows Committee has selected less than 0.1% of members as new fellows.

Also honored by AGU this year are three 91±¬ĮĻ faculty members, from the departments of Earth and space sciences and atmospheric sciences, who have received other awards.

Here are the 91±¬ĮĻā€™s five new AGU Fellows:

, professor of Earth and space sciences, studies which characteristics of Earth help this planet support life, and whether life might be found on other planets. His work spans astronomy, biology and geology, on planetary environments including Earth, Mars, Venus and icy moons, as well as planets outside this solar system. He is the author of ā€œAstrobiology: A Very Short Introductionā€ for the layperson and ā€œAtmospheric Evolution on Inhabited and Lifeless Worldsā€ for researchers.

, who holds the Karl M. Banse Endowed Professorship in oceanography, explores the limits and ecological contributions of microbial life in deep ocean and polar regions, focusing in recent years on how microbes adapt to the extreme conditions of Arctic sea ice. In addition to a research and teaching career, Deming founded what is now the 91±¬ĮĻ Center for Environmental Genomics and helped establish the nationā€™s first graduate training program in astrobiology.

, professor of global health and of environmental and occupational health sciences, has been conducting research on the health risks of climate variability and change for nearly 30 years. She focuses on estimating current and future health risks of climate change, designing adaptation policies and measures to reduce risks in multi-stressor environments, and estimating the health co-benefits of mitigation policies. Ebi is also founding director of the 91±¬ĮĻ , or CHanGE.

, professor of astronomy, is an astrobiologist and planetary astronomer whose research focuses onĀ predicting, acquiring and analyzing observations of planetary atmospheres and surfaces. In addition to studying planets within our solar system, she is interested in exoplanets ā€” those outside the solar system ā€” andĀ how they might reveal the presence of life. With the 91±¬ĮĻā€™s Virtual Planetary Laboratory, she uses models of planets and planet-star interactions to generate plausible planetary environments and spectra for extrasolar terrestrial planets and the early Earth.

, professor and chair of Earth and space sciences, is a geochemist and glaciologist whose research focuses on polar climate and ice sheets in the Arctic and in Antarctica. He is best known for his analyses of Antarctic ice cores using measurements of oxygen and hydrogen in the ice to better understand how climate has varied in the past, over hundreds to thousands of years.

In addition to the newly elected fellows, 91±¬ĮĻ faculty members are also recognized in several subject-specific awards and lectures:

, professor of atmospheric sciences, will deliver the in December at the AGUā€™s fall meeting. Alexander studies the relationship between climate change and the chemical composition of the atmosphere. She looks at the pathways by which atmospheric pollutants form, how those chemical pathways can vary, and what that means both for present-day air quality and for the future of climate change.

, research assistant professor of Earth and space sciences, has received the for his research modeling natural disasters using geodesy, or the shape of the Earthā€™s surface, and seismology. Crowell pioneered ways to use GPS and related data in earthquake and tsunami early warning systems. He is currently using this data to better understand natural disasters as they unfold and develop a risk-mitigation framework for coastal hazards such as tsunamis.

, research assistant professor of Earth and space sciences, has received the . Journaux uses modeling and experiments to explore the conditions in extreme environments on other planets, and how that might affect their ability to harbor life. He is a member of the science team for NASAā€™s upcoming Dragonfly mission, which will characterize the chemistry and habitability of Saturnā€™s largest moon, Titan.

, a researcher at the Pacific Northwest National Laboratory with an affiliate 91±¬ĮĻ faculty position in oceanography, has received the .

All honorees will be recognized in December at the AGUā€™s fall meeting in San Francisco.

Something was holding back oxygenā€™s rise. A new interpretation of rocks billions of years old finds volcanic gases are the likely culprits. The led by the 91±¬ĮĻ was published in June in the open-access journal Nature Communications.

ā€œThis study revives a classic hypothesis for the evolution of atmospheric oxygen,ā€ said lead author , a 91±¬ĮĻ postdoctoral researcher in Earth and space sciences. ā€œThe data demonstrates that an evolution of the mantle of the Earth could control an evolution of the atmosphere of the Earth, and possibly an evolution of life.ā€

Multicellular life needs a concentrated supply of oxygen, so the accumulation of oxygen is key to the evolution of oxygen-breathing life on Earth.

ā€œIf changes in the mantle controlled atmospheric oxygen, as this study suggests, the mantle might ultimately set a tempo of the evolution of life,ā€ Kadoya said.

The new work builds on a 2019 that found the early Earthā€™s mantle was far less oxidized, or contained more substances that can react with oxygen, than the modern mantle. That study of ancient volcanic rocks, up to 3.55 billion years old, were collected from sites that included South Africa and Canada.

at Scripps Institution of Oceanography, at the University of Maryland, and at Arizona State University are among the authors of the 2019 study. They are also co-authors of the new paper, looking at how changes in the mantle influenced the volcanic gases that escaped to the surface.

The Archean Eon, when only microbial life was widespread on Earth, was more volcanically active than today. Volcanic eruptions are fed by magma ā€“ a mixture of molten and semi-molten rock ā€“ as well as gases that escape even when the volcano is not erupting.

Some of those gases react with oxygen, or oxidize, to form other compounds. This happens because oxygen tends to be hungry for electrons, so any atom with one or two loosely held electrons reacts with it. For instance, hydrogen released by a volcano combines with any free oxygen, removing that oxygen from the atmosphere.

The chemical makeup of Earthā€™s mantle, or softer layer of rock below the Earthā€™s crust, ultimately controls the types of molten rock and gases coming from volcanoes. A less-oxidized early mantle would produce more of the gases like hydrogen that combine with free oxygen. The 2019 paper shows that the mantle became gradually more oxidized from 3.5 billion years ago to today.

The new study combines that data with evidence from ancient sedimentary rocks to show a tipping point sometime after 2.5 billion years ago, when oxygen produced by microbes overcame its loss to volcanic gases and began to accumulate in the atmosphere.

ā€œBasically, the supply of oxidizable volcanic gases was capable of gobbling up photosynthetic oxygen for hundreds of millions of years after photosynthesis evolved,ā€ said co-author , a 91±¬ĮĻ professor of Earth and space sciences. ā€œBut as the mantle itself became more oxidized, fewer oxidizable volcanic gases were released. Then oxygen flooded the air when there was no longer enough volcanic gas to mop it all up.ā€

This has implications for understanding the emergence of complex life on Earth and the possibility of life on other planets.

ā€œThe study indicates that we cannot exclude the mantle of a planet when considering the evolution of the surface and life of the planet,ā€ Kadoya said.

This research was funded by the National Science Foundation.

For more information, contact Kadoya at skadoya@uw.edu or Catling at dcatling@uw.edu.

Very occasionally, Earth gets bombarded by a large meteorite. But every day, our planet gets pelted by space dust, micrometeorites that collect on Earth’s surface.

A 91±¬ĮĻ team looked at very old samples of these small meteorites to show that the grains could have reacted with carbon dioxide on their journey to Earth. Previous work suggested the meteorites ran into oxygen, contradicting theories and evidence that the Earth’s early atmosphere was virtually devoid of oxygen. The new was published this week in the open-access journal Science Advances.

“Our finding that the atmosphere these micrometeorites encountered was high in carbon dioxide is consistent with what the atmosphere was thought to look like on the early Earth,” said first author , a 91±¬ĮĻ doctoral student in Earth and space sciences.

At 2.7 billion years old, these are the oldest known micrometeorites. They were collected in limestone in the Pilbara region of Western Australia and fell during the Archean eon, when the sun was weaker than today. A 2016 paper by the team that discovered the samples suggested they at the time they fell to Earth.

That interpretation would contradict current understandings of our planet’s early days, which is that oxygen rose during the “,” almost half a billion years later.

Knowing the conditions on the early Earth is important not just for understanding the history of our planet and the conditions when life emerged. It can also help inform the search for life on other planets.

“Life formed more than 3.8 billion years ago, and how life formed is a big, open question. One of the most important aspects is what the atmosphere was made up of ā€” what was available and what the climate was like,” Lehmer said.

The new study takes a fresh look at interpreting how these micrometeorites interacted with the atmosphere, 2.7 billion years ago. The sand-sized grains hurtled toward Earth at up to 20 kilometers per second. For an atmosphere of similar thickness to today, the metal beads would melt at about 80 kilometers elevation, and the molten outer layer of iron would then oxidize when exposed to the atmosphere. A few seconds later the micrometeorites would harden again for the rest of their fall. The samples would then remain intact, especially when protected under layers of sedimentary limestone rock.

The previous paper interpreted the oxidization on the surface as a sign that the molten iron had encountered molecular oxygen. The new study uses modeling to ask whether carbon dioxide could have provided the oxygen to produce the same result. A computer simulation finds that an atmosphere made up of from 6% to more than 70% carbon dioxide could have produced the effect seen in the samples.

“The amount of oxidation in the ancient micrometeorites suggests that the early atmosphere was very rich in carbon dioxide,” said co-author , a 91±¬ĮĻ professor of Earth and space sciences.

For comparison, carbon dioxide concentrations today are rising and are currently at about 415 parts per million, or 0.0415% of the atmosphere’s composition.

High levels of carbon dioxide, a heat-trapping greenhouse gas, would counteract the sun’s weaker output during the Archean era. Knowing the exact concentration of carbon dioxide in the atmosphere could help pinpoint air temperature and and acidity of the oceans during that time.

More of the ancient micrometeorite samples could help narrow the range of possible carbon dioxide concentrations, the authors wrote. Grains that fell at other times could also help trace the history of Earth’s atmosphere through time.

“Because these iron-rich micrometeorites can oxidize when they are exposed to carbon dioxide or oxygen, and given that these tiny grains presumably are preserved throughout Earth’s history, they could provide a very interesting proxy for the history of atmospheric composition,” Lehmer said.

Other co-authors are , a 91±¬ĮĻ professor emeritus of astronomy; , a 91±¬ĮĻ professor of Earth and space sciences; and , a former 91±¬ĮĻ undergraduate who is now at Rutgers University. The research was funded by NASA, the 91±¬ĮĻ Astrobiology Program, the 91±¬ĮĻ Virtual Planetary Laboratory and the Simons Foundation’s Collaboration on the Origins of Life.

For more information, contact Lehmer at olehmer@uw.edu or Catling at 206-543-8653 or dcatling@uw.edu.

But how did a lifeless environment on the early Earth supply this key ingredient?

“For 50 years, what’s called ‘the phosphate problem,’ has plagued studies on the origin of life,” said first author , a 91±¬ĮĻ research assistant professor of Earth and space sciences.

The problem is that chemical reactions that make the building blocks of living things need a lot of phosphorus, but phosphorus is scarce. A new 91±¬ĮĻ study, published Dec. 30 in the Proceedings of the National Academy of Sciences, finds an answer to this problem in certain types of lakes.

The focuses on carbonate-rich lakes, which form in dry environments within depressions that funnel water draining from the surrounding landscape. Because of high evaporation rates, the lake waters concentrate into salty and alkaline, or high-pH, solutions. Such lakes, also known as alkaline or soda lakes, are found on all seven continents.

The researchers first looked at phosphorus measurements in existing carbonate-rich lakes, including in California, in Kenya and in India.

While the exact concentration depends on where the samples were taken and during what season, the researchers found that carbonate-rich lakes have up to 50,000 times phosphorus levels found in seawater, rivers and other types of lakes. Such high concentrations point to the existence of some common, natural mechanism that accumulates phosphorus in these lakes.

Today these carbonate-rich lakes are biologically rich and support life ranging from microbes to Lake Magadi’s famous flocks of flamingoes. These living things affect the lake chemistry. So researchers did lab experiments with bottles of carbonate-rich water at different chemical compositions to understand how the lakes accumulate phosphorus, and how high phosphorus concentrations could get in a lifeless environment.

The reason these waters have high phosphorus is their carbonate content. In most lakes, calcium, which is much more abundant on Earth, binds to phosphorus to make solid calcium phosphate minerals, which life can’t access. But in carbonate-rich waters, the carbonate outcompetes phosphate to bind with calcium, leaving some of the phosphate unattached. Lab tests that combined ingredients at different concentrations show that calcium binds to carbonate and leaves the phosphate freely available in the water.

“It’s a straightforward idea, which is its appeal,” Toner said. “It solves the phosphate problem in an elegant and plausible way.”

Phosphate levels could climb even higher, to a million times levels in seawater, when lake waters evaporate during dry seasons, along shorelines, or in pools separated from the main body of the lake.

“The extremely high phosphate levels in these lakes and ponds would have driven reactions that put phosphorus into the molecular building blocks of RNA, proteins, and fats, all of which were needed to get life going,” said co-author , a 91±¬ĮĻ professor of Earth & space sciences.

The carbon dioxide-rich air on the early Earth, some four billion years ago, would have been ideal for creating such lakes and allowing them to reach maximum levels of phosphorus. Carbonate-rich lakes tend to form in atmospheres with high carbon dioxide. Plus, carbon dioxide dissolves in water to create acid conditions that efficiently release phosphorus from rocks.

“The early Earth was a volcanically active place, so you would have had lots of fresh volcanic rock reacting with carbon dioxide and supplying carbonate and phosphorus to lakes,” Toner said. “The early Earth could have hosted many carbonate-rich lakes, which would have had high enough phosphorus concentrations to get life started.”

Another recent by the two authors showed that these types of lakes can also provide abundant cyanide to support the formation of amino acids and nucleotides, the building blocks of proteins, DNA and RNA. Before then researchers had struggled to find a natural environment with enough cyanide to support an origin of life. Cyanide is poisonous to humans, but not to primitive microbes, and is critical for the kind of chemistry that readily makes the building blocks of life.

The research was funded by the Simons Foundation’s Collaboration on the Origins of Life.

For more information, contact Toner at 267-304-3488 or toner2@uw.edu and Catling at 206-543-8653 or dcatling@uw.edu.

is the study of life in the universe and of the terrestrial environments and planetary and stellar processes that support it. To study astrobiology is to ask questions that cut across multiple disciplines and could take lifetimes to answer. The field gathers expertise from a host of other disciplines including biology, chemistry, geology, oceanography, atmospheric and Earth science, aeronautical engineering and of course astronomy itself.

These questions also include: What can Earthā€™s own species, and its chemical past, tell us about how to spot life elsewhere? How did the first cells arise? Can we map the surfaces of exoplanets? How can we motivate students to be curious about space?

Every two years, researchers gather from around the world to share and discuss their latest findings in a weeklong conference. Called for short, this yearā€™s conference will be held June 24-28 at the Hyatt Regency Hotel in Bellevue. Itā€™s the biggest meeting of astrobiologists in the world and dozens of 91±¬ĮĻ researchers will attend and participate.

Public attitudes have warmed greatly toward astrobiology in the 21^st century, prompted by exoplanet discoveries and exploration of other worlds in the solar system. Study of extraterrestrial life remains a hopeful science wryly aware that, as an old joke goes, it has yet to prove that its very subject matter exists.

The 91±¬ĮĻ founded its own program in 1999, involving roughly 30 faculty and about as many students a year. “The program is a leader in both training the next generation of astrobiologists and in fundamental astrobiology research,” said , 91±¬ĮĻ professor of astronomy and principal investigator for the 91±¬ĮĻ-based , which explores computer models of planetary environments and will be the subject of a .

“The Astrobiology Science Conference is the biggest meeting of astrobiologists in the world, and this year, members of the 91±¬ĮĻ Astrobiology Program are playing a major role in conference organization, as well as presenting our research at the meeting,” said Meadows, who chaired the science committee for AcSciCon2019.

Here are several 91±¬ĮĻ presentations and papers scheduled for the weeklong conference. Though the lead presenter is listed here only, most projects involve the work of several colleagues.

• A study of water vapor and ice particles emitting from the plume on Saturn’s moon Enceladus, leading to a better understanding of the moon’s subsurface ocean. With Earth and space sciences doctoral student and colleagues. ()
• An examination of whether the coming James Webb Space Telescope will be able to detect atmospheres for all worlds in the intriguing, seven-planet system TRAPPIST-1, and finding that clouds and water vapor in the planets’ atmospheres might make such study more challenging. With astronomy and astrobiology doctoral student and colleagues. ()
• Description of a new open-source computer software package called VPLanet that simulates a wide range of planetary systems across billions of years, simulating atmospheres, orbits and stellar phenomena that can affect a planet’s ability to sustain liquid water on its surface, which is key to life. With Rory Barnes and colleagues. ()
• An exploration of how viruses and hosts co-evolved, enabling microbial life in extremely cold brines. With oceanography professor ().
• Modeling Earth’s atmosphere 2.7 billion years ago and the effect of iron-rich micrometeorites that rained down, melted and interacted with the surrounding gases, leading to a better understanding of carbon dioxide levels at that time. With Earth and space sciences graduate student and colleagues. ()
• A presentation on the 91±¬ĮĻ Astronomy Department’s successful outreach to students through its that visits K-12 schools, enabling them to create shows of their own. With astronomy research assistant professor and several colleagues. and .)
• An exploration of how to determine if oxygen detected on an exoplanet is really produced by life, using high-resolution planetary spectra from ground-based telescopes. With , an astronomy doctoral student, and colleagues. ()
• A discussion of how studying a giant Pacific Octopus might help us learn more about different forms of cognition and better know and understand life beyond Earth ā€” if we ever find it. With , a doctoral student in psychology. ()
• A study of microbial life in extremely cold brines within unfrozen subsurface areas of permafrost, and their possible relevance to similar environments on Mars or icy moons in the solar system. With , a doctoral student in biological oceanography, and colleagues. (.)

Many other 91±¬ĮĻ faculty members will participate, either with reports on their own research or in support of colleagues or graduate students. These include ESS professors , , , , , astronomy professors , and , among others.

Astrobiologists such as Sullivan point out that the fieldā€™s focus and scientific benefit is about more than simply hunting for life, though that is the key motivator.

“Itā€™s about thinking about life in a cosmic context. And about the origin and evolution of life,” Sullivan said.

“Even if you only care about Earth life, astrobiology is a viable ā€” fundamental, I would say ā€” interdisciplinary science that thrives independently of the existence of extraterrestrial life.ā€

The subsurface ocean of Saturn’s moon probably has higher than previously known concentrations of carbon dioxide and hydrogen and a more Earthlike pH level, possibly providing conditions favorable to life, according to new research from planetary scientists at the 91±¬ĮĻ.

The presence of such high concentrations could provide fuel ā€” a sort of chemical ā€œfree lunchā€ ā€” for living microbes, said lead researcher a 91±¬ĮĻ doctoral student in Earth and space sciences. Or, it could mean ā€œthat there is hardly anyone around to eat it.ā€

The new information about the composition of Enceladusā€™ ocean gives planetary scientists a better understanding of the ocean worldā€™s capacity to host life. Fifer said.

Enceladus is a small moon, an ocean world about 310 miles (500 kilometers) across. Its salty subsurface ocean is of interest because of the similarity in pH, salinity and temperature to Earth’s oceans. Plumes of water vapor and ice particles ā€” spotted and studied by the spacecraft ā€” erupting hundreds of miles into space from the ocean through cracks in Enceladus’s ice-encased surface provide a tantalizing glimpse into what the moonā€™s subsurface ocean might contain.

But Fifer and colleagues found that the plumes arenā€™t chemically the same as the ocean from which they erupt at 800 miles an hour; the eruption process itself changes their composition. He is working with ESS faculty members and . They will present their work June 24 at the .

Fifer and colleagues say the plumes provide an “imperfect window” to the composition of Enceladusā€™s global subsurface ocean and that the plume composition and ocean composition could be much different. That, they find, is due to plume , or the separation of gases, which preferentially allows some components of the plume to erupt while others are left behind.

This in mind, the team returned to data from the Cassini mission with a computer simulation that accounts for the effects of fractionation, to get a clearer idea of the composition of Enceladusā€™s inner oceanā€™s. They found ā€œsignificant differencesā€ between Enceladusā€™s plume and ocean chemistry. Previous interpretations, they found, underestimate the presence of hydrogen, methane and carbon dioxide in the ocean.

ā€œItā€™s better to find high gas concentrations than none at all,ā€ said Fifer. ā€œIt seems unlikely that life would evolve to consume this chemical free lunch if the gases were not abundant in the ocean.ā€

Those high levels of carbon dioxide also imply a lower and more Earthlike pH level in the ocean of Enceladus than previous studies have shown. This bodes well for possible life, too, Fifer said.

“Although there are exceptions, most life on Earth functions best living in or consuming water with near-neutral pH, so similar conditions on Enceladus could be encouraging,” he said. “And they make it much easier to compare this strange ocean world to an environment that is more familiar.”

There could be high concentrations of ammonium as well, which is also a potential fuel for life. And though the high concentrations of gases might indicate a lack of living organisms to consume it all, Fifer said, that does not necessarily mean Enceladus is devoid of life. It might mean microbes just arenā€™t abundant enough to consume all the available chemical energy.

The researchers can use the gas concentrations to determine an upper limit for certain types of possible life that could exist in the icy ocean of Enceladus.

In other words, he said: “Given that there’s so much free lunch available, what’s the greatest amount that life could be eating to still leave behind the amount we see? How much life would that support?”

Thanks to Cassini, he said, we know about Enceladus’ ocean and the types of gases, salts and organic compounds that are present there. Studying how the plume composition changes can teach us yet more about this ocean and everything in it.

“Future spacecraft missions will sample the plumes looking for signs of life, many of which will be affected just by the eruption process,” Fifer said. “So, understanding the difference between the ocean and the plume now will be a huge help down the road.”

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For more information, contact Fifer at lufifer@uw.edu.

Researchers with the 91±¬ĮĻ-led are central to a group of published by NASA researchers in the journal Astrobiology outlining the history ā€” and suggesting the future ā€” of the search for life on exoplanets, or those orbiting stars other than the sun.

The research effort is coordinated by NASAā€™s Nexus for Exoplanet Systems Science, or NExSS, a worldwide network dedicated to finding new ways to study the age-old question: ā€œAre we alone?ā€

A theme through the research and the discussions behind it is the need to consider planets in an integrated way, involving multiple disciplines and perspectives.

ā€œFor life to be detectable on a distant world it needs to strongly modify its planet in a way that we can detect,ā€ said 91±¬ĮĻ astronomy professor , lead author of one of the papers and principle investigator of the Virtual Planetary Laboratory, or VPL for short. “But for us to correctly recognize lifeā€™s impact, we also need to understand the planet and star ā€” that environmental context is key.”

Work done by NExSS researchers will help identify the measurements and instruments needed to search for life using future NASA flagship missions. The detection of atmospheric signatures of a few potentially habitable planets may possibly come before 2030, although whether the planets are truly habitable or have life will require more in-depth study.

The papers result from two years of effort by some of the worldā€™s leading researchers in astrobiology, planetary science, Earth science, , astrophysics, chemistry and biology, including several from the 91±¬ĮĻ and the Virtual Planetary Laboratory, or VPL. The coordinated work was born of online meetings and an in-person workshop held in Seattle in July of 2016.

The pace of exoplanet discoveries has been rapid, with over 3,700 detected since 1992. NASA formed the international NExSS network to focus a variety of disciplines on understanding how we can characterize and eventually search for signs of life, called biosignatures, on exoplanets.

The NExSS network has furthered the field of exoplanet biosignatures and ā€œfostered communication between researchers searching for signs of life on solar system bodies with those searching for signs of life on exoplanets,ā€ said Niki Parenteau, an astrobiologist and microbiologist at NASAā€™s Ames Research Center, Moffett Field, California, and a VPL team member. ā€œThis has allowed for sharing of ā€˜lessons learnedā€™ by both communities.ā€

The first of the papers reviews types of signatures astrobiologists have proposed as ways to identify life on an exoplanet. Scientists plan to look for two major types of signals: One is in the form of gases that life produces, such as oxygen made by plants or photosynthetic microbes. The other could come from the light reflected by life itself, such as the color of leaves or pigments.

Such signatures can be seen on Earth from orbit, and astronomers are studying designs of telescope concepts that may be able to detect them on planets around nearby stars. Meadows is a co-author, and lead author is , a VPL team member who earned his doctorate in astronomy and astrobiology from the 91±¬ĮĻ and is now a post-doctoral researcher at the University of California, Riverside.

Meadows is lead author of the second review paper, which discusses recent research on “false positives” and “false negatives” for biosignatures, or ways nature could ā€œtrickā€ scientists into thinking a planet without life was alive, or vice versa.

In this paper, Meadows and co-authors review ways that a planet could make oxygen abiotically, or without the presence of life, and how planets with life may not have the signature of oxygen that is abundant on modern-day Earth.

The paper’s purpose, Meadows said, was to discuss these changes in our understanding of biosignatures and suggest “a more comprehensive” treatment.Ā  She said: “There are lots of things in the universe that could potentially put two oxygen atoms together, not just photosynthesis ā€” let’s try to figure out what they are. Under what conditions are they are more likely to happen, and how can we avoid getting fooled?”

Schwieterman is a co-author on this paper, as well as 91±¬ĮĻ doctoral students , and .

With such advance thinking, scientists are now better prepared to distinguish false positives from planets that truly do host life.

Two more papers show how scientists try to formalize the lessons we have learned from Earth, and expand them to the wide diversity of worlds we have yet to discover.

, 91±¬ĮĻ professor of Earth and space sciences, is lead author on a paper that proposes a framework for assessing exoplanet biosignatures, considering such variables as the chemicals in the planetā€™s atmosphere, the presence of oceans and continents and the world’s overall climate. Doctoral student is a co-author.

By combining all this information in systematic ways, scientists can analyze whether data from a planet can be better explained statistically by the presence of life, or its absence.

ā€œIf future data from an exoplanet perhaps suggest life, what approach can distinguish whether the existence of life is a near-certainty or whether the planet is really as dead as a doornail?ā€ said Catling. ā€œBasically, NASA asked us to work out how to assign a probability to the presence of exoplanet life, such as a 10, 50 or 90 percent chance. Our paper presents a general method to do this.ā€

The data that astronomers collect on exoplanets will be sparse. They will not have samples from these distant worlds, and in many cases will study the planet as a single point of light. By analyzing these fingerprints of atmospheric gases and surfaces embedded in that light, they will discern as much as possible about the properties of that exoplanet.

“Because life, planet, and parent star change with time together, a biosignature is no longer a single target but a suite of system traits,” said , a biometeorologist at NASAā€™s Goddard Institute for Space Studies in New York and a VPL team member. She said more biologists and geologists will be needed to interpret observations “where life processes will be adapted to the particular environmental context.ā€

The final article discusses the ground-based and space-based telescopes that astronomers will use to search for life beyond the solar system. This includes a variety of observatories, from those in operation today to ones that will be built decades in the future.

Taken together, this cluster of papers explains how the exoplanet community will evolve from their current assessments of the sizes and orbits of these faraway worlds, to thorough analysis of their chemical composition and eventually whether they harbor life.

ā€œIā€™m excited to see how this research progresses over the coming decades,ā€ said , an astrobiologist at NASAā€™s Goddard Space Flight Center, Greenbelt, Maryland, and a VPL team member. He is also a co-author on four of the five papers.

ā€œNExSS has created a diverse network of scientists. That network will allow the community to more rigorously assess planets for biosignatures than would have otherwise been possible.ā€

NExSS is an interdisciplinary, cross-divisional NASA research coordination network.

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Based on a . For more information, contact Meadows at vsm@astro.washington.edu or Catling at dcatling@uw.edu.

New from the 91±¬ĮĻ suggests a milder youth for our planet. An analysis of temperature through early Earth’s history, published the week of April 2 in the Proceedings of the National Academy of Sciences, supports more moderate average temperatures throughout the billions of years when life slowly emerged on Earth.

“Ideas about the early Earth’s environment are all over the place, from a very hot world, to one locked in a permanent ice age, from a world with acidic oceans to one with seawater so alkaline it would sting your eyes,” said , a 91±¬ĮĻ professor of Earth and space sciences. “These simulations show that our early world had about the same average temperature as today, and a seawater pH within roughly one unit of neutral.”

Previous research studies have put average temperatures during the era, 4 to 2.5 billion years ago, as low as minus 25 degrees Celsius. Other estimates, based on different interpretations of the evidence, have placed average temperatures as high as 85 degrees Celsius, under which only heat-loving microbes that now exist in hot springs could survive.

The new results put the outer range of possible temperatures at 0 to 50 C (32 to 122 F).

“Our results show that Earth has had a moderate temperature through virtually all of its history, and that is attributable to weathering feedbacks ā€” they do a good job at maintaining a habitable climate,” said first author , a 91±¬ĮĻ doctoral student in Earth and space sciences.

To create their estimate, the researchers took the most recent understanding for how rocks, oceans and air temperature interact, and put that into a computer simulation of Earth’s temperature over the past 4 billion years. Their calculations included the most recent information for how seafloor weathering occurs on geologic timescales, and under different conditions.

Though we don’t think of wind and rain wearing away at the seafloor, the seabed is eroded as seawater percolates through rock on the ocean’s floor. Carbon-containing molecules settle out from the water, a process related to the temperature and acidity of the seawater, while other chemicals are dissolved from the rock.

“Seafloor weathering was more important for regulating temperature of the early Earth because there was less continental landmass at that time, the Earth’s interior was even hotter, and the seafloor crust was spreading faster, so that was providing more crust to be weathered,” Krissansen-Totton said.

The authors ran simulations for many possible scenarios for the size of the continents, the temperature sensitivity of chemical weathering and other factors to get the full range of possible scenarios for average air temperature and ocean pH through history.

“We got this initial answer that early Earth had moderate temperatures and slightly acidic ocean pH,” Krissansen-Totton said. “I tried really hard to break that, looking for assumptions that could possibly change that answer. But I found that this is a really robust result. It’s hard to imagine a realistic scenario where temperatures or pH were more extreme.”

That is good news for the search for life on other planets. If Earth’s temperature was moderate throughout its history, other planets located in the habitable zone must also retain a fairly stable climate long enough for other lifeforms to evolve.

“There’s nothing particularly remarkable about these processes,” Krissansen-Totton said. “They can occur on any rocky planet with oceans. So other planets that are in the habitable zone are likely to have their climates stabilized to moderate values by these weathering feedbacks. And that’s a good thing for the search for life, because you need moderate temperatures for billions of years to have a stable environment for life to evolve.”

The results may also help shed light on what conditions were like during the early evolution of life on Earth.

“The results help us understand how natural processes kept Earth’s environment suitable for life to carry on for billions of years, from its humblest beginnings to the wonderful forms now around us,” Catling said.

The paper’s other co-author is , a research scientist at NASA who contributed as part of her 91±¬ĮĻ doctorate. The research was funded by NASA and the Simons Foundation.

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For more information, contact Krissansen-Totton at joshkt@uw.edu or 206-402-7007 and Catling at dcatling@uw.edu.

Grants: NASA: NNX15AR63H, NNA13AA93A, NNX15AL23G, Simons Foundation: 511570