A new analysis of 2.5-billion-year-old rocks from Australia finds that volcanic eruptions may have stimulated population surges of marine microorganisms, creating the first puffs of oxygen into the atmosphere. This would change existing stories of Earth’s early atmosphere, which assumed that most changes in the early atmosphere were controlled by geologic or chemical processes.

Though focused on Earth’s early history, the research also has implications for extraterrestrial life and even climate change. The led by the 91̽��, the University of Michigan and other institutions was published in August in the Proceedings of the National Academy of Sciences.

“What has started to become obvious in the past few decades is there actually are quite a number of connections between the solid, nonliving Earth and the evolution of life,” said first author , a 91̽��doctoral student in Earth and space sciences. “But what are the specific connections that facilitated the evolution of life on Earth as we know it?”

In its earliest days, Earth had no oxygen in its atmosphere and few, if any, oxygen-breathing lifeforms. Earth’s atmosphere became permanently oxygen-rich about 2.4 billion years ago, likely after an explosion of lifeforms that photosynthesize, transforming carbon dioxide and water into oxygen.

But in 2007, co-author at Arizona State University analyzed rocks from the Mount McRae Shale in Western Australia, reporting a of oxygen about 50 to 100 million years before it became a permanent fixture in the atmosphere. More recent research has confirmed other, earlier short-term oxygen spikes, but hasn’t explained their rise and fall.

In the new study, researchers at the University of Michigan, led by co-corresponding author , analyzed the same ancient rocks for the concentration and number of neutrons in the element mercury, emitted by volcanic eruptions. Large volcanic eruptions blast mercury gas into the upper atmosphere, where today it circulates for a year or two before raining out onto Earth’s surface. The new analysis shows a spike in mercury a few million years before the temporary rise in oxygen.

“Sure enough, in the rock below the transient spike in oxygen we found evidence of mercury, both in its abundance and isotopes, that would most reasonably be explained by volcanic eruptions into the atmosphere,” said co-author , a 91̽��professor of Earth and Space Sciences.

Where there were volcanic emissions, the authors reason, there must have been lava and volcanic ash fields. And those nutrient-rich rocks would have weathered in the wind and rain, releasing phosphorus into rivers that could fertilize nearby coastal areas, allowing oxygen-producing cyanobacteria and other single-celled lifeforms to flourish.

“There are other nutrients that modulate biological activity on short timescales, but phosphorus is the one that is most important on long timescales,” Meixnerová said.

Today, phosphorus is plentiful in biological material and in agricultural fertilizer. But in very ancient times, weathering of volcanic rocks would have been the main source for this scarce resource.

“During weathering under the Archaean atmosphere, the fresh basaltic rock would have slowly dissolved, releasing the essential macro-nutrient phosphorus into the rivers. That would have fed microbes that were living in the shallow coastal zones and triggered increased biological productivity that would have created, as a byproduct, an oxygen spike,” Meixnerová said.

The precise location of those volcanoes and lava fields is unknown, but large lava fields of about the right age exist in modern-day India, Canada and elsewhere, Buick said.

“Our study suggests that for these transient whiffs of oxygen, the immediate trigger was an increase in oxygen production, rather than a decrease in oxygen consumption by rocks or other nonliving processes,” Buick said. “It’s important because the presence of oxygen in the atmosphere is fundamental – it’s the biggest driver for the evolution of large, complex life.”

Ultimately, researchers say the study suggests how a planet’s geology might affect any life evolving on its surface, an understanding that aids in identifying habitable exoplanets, or planets outside our solar system, in the search for life in the universe.

Other authors of the paper are co-corresponding author , a former 91̽��astrobiology graduate student now at the University of St. Andrews in Scotland; , a former 91̽��graduate student now at the California Institute of Technology; and at the University of Michigan. The study was funded by NASA, the NASA-funded 91̽�� team and the MacArthur Professorship to Blum at the University of Michigan.

For more information contact Meixnerová at janameix@uw.edu or Buick at buick@uw.edu. Note: Meixnerová is on European Time; Buick is on Pacific Time.

NASA: NNX16AI37G, 80NSSC18K0829

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 91̽�� 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 91̽��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 — 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 91̽��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 91̽��professor emeritus of astronomy; , a 91̽��professor of Earth and space sciences; and , a former 91̽��undergraduate who is now at Rutgers University. The research was funded by NASA, the 91̽��Astrobiology Program, the 91̽��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.

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 Earth’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 year’s conference will be held June 24-28 at the Hyatt Regency Hotel in Bellevue. It’s the biggest meeting of astrobiologists in the world and dozens of 91̽�� 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 91̽��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 , 91̽��professor of astronomy and principal investigator for the UW-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 91̽��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 91̽��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 91̽��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 — 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 91̽��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 field’s focus and scientific benefit is about more than simply hunting for life, though that is the key motivator.

“It’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 — fundamental, I would say — interdisciplinary science that thrives independently of the existence of extraterrestrial life.”

Earth’s oxygen levels rose and fell more than once hundreds of millions of years before the planetwide success of the Great Oxidation Event about 2.4 billion years ago, new research from the 91̽�� shows.

The evidence comes from a new study that indicates a second and much earlier “whiff” of oxygen in Earth’s distant past — in the atmosphere and on the surface of a large stretch of ocean — showing that the oxygenation of the Earth was a complex process of repeated trying and failing over a vast stretch of time.

The finding also may have implications in the search for life beyond Earth. Coming years will bring powerful new ground- and space-based telescopes able to analyze the atmospheres of distant planets. This work could help keep astronomers from unduly ruling out “false negatives,” or inhabited planets that may not at first appear to be so due to undetectable oxygen levels.

“The production and destruction of oxygen in the ocean and atmosphere over time was a war with no evidence of a clear winner, until the Great Oxidation Event,” said , a 91̽��doctoral student in Earth and space sciences and lead author of a new published the week of July 9 in the Proceedings of the National Academy of Sciences.

“These transient oxygenation events were battles in the war, when the balance tipped more in favor of oxygenation.”

In 2007, co-author , 91̽��professor of Earth and space sciences, was part of an international team of scientists that found evidence of an episode — a “whiff” — of oxygen some 50 million to 100 million years before the Great Oxidation Event. This they learned by drilling deep into sedimentary rock of the Mount McRae Shale in Western Australia and analyzing the samples for the trace metals molybdenum and rhenium, accumulation of which is dependent on oxygen in the environment.

Now, a team led by Koehler has confirmed a second such appearance of oxygen in Earth’s past, this time roughly 150 million years earlier — or about 2.66 billion years ago — and lasting for less than 50 million years. For this work they used two different proxies for oxygen — nitrogen isotopes and the element selenium — substances that, each in its way, also tell of the presence of oxygen.

“What we have in this paper is another detection, at high resolution, of a transient whiff of oxygen,” said Koehler. “Nitrogen isotopes tell a story about oxygenation of the surface ocean, and this oxygenation spans hundreds of kilometers across a marine basin and lasts for somewhere less than 50 million years.”

The team analyzed drill samples taken by Buick in 2012 at another site in the northwestern part of Western Australia called the Jeerinah Formation.

The researchers drilled two cores about 300 kilometers apart but through the same sedimentary rocks — one core samples sediments deposited in shallower waters, and the other samples sediments from deeper waters. Analyzing successive layers in the rocks years shows, Buick said, a “stepwise” change in nitrogen isotopes “and then back again to zero. This can only be interpreted as meaning that there is oxygen in the environment. It’s really cool — and it’s sudden.”

The nitrogen isotopes reveal the activity of certain marine microorganisms that use oxygen to form nitrate, and other microorganisms that use this nitrate for energy. The data collected from nitrogen isotopes sample the surface of the ocean, while selenium suggests oxygen in the air of ancient Earth. Koehler said the deep ocean was likely anoxic, or without oxygen, at the time.

The team found plentiful selenium in the shallow hole only, meaning that it came from the nearby land, not making it to deeper water. Selenium is held in sulfur minerals on land; higher atmospheric oxygen would cause more selenium to be leached from the land through oxidative weathering — “the rusting of rocks,” Buick said — and transported to sea.

“That selenium then accumulates in ocean sediments,” Koehler said. “So when we measure a spike in selenium abundances in ocean sediments, it could mean there was a temporary increase in atmospheric oxygen.”

The finding, Buick and Koehler said, also has relevance for detecting life on exoplanets, or those beyond the solar system.

“One of the strongest atmospheric biosignatures is thought to be oxygen, but this study confirms that during a planet’s transition to becoming permanently oxygenated, its surface environments may be oxic for intervals of only a few million years and then slip back into anoxia,” Buick said.

“So, if you fail to detect oxygen in a planet’s atmosphere, that doesn’t mean that the planet is uninhabited or even that it lacks photosynthetic life. Merely that it hasn’t built up enough sources of oxygen to overwhelm the ‘sinks’ for any longer than a short interval.

“In other words, lack of oxygen can easily be a ‘false negative’ for life.”

Koehler added: “You could be looking at a planet and not see any oxygen — but it could be teeming with microbial life.”

Koehler’s other co-authors are 91̽��Earth and space sciences doctoral student , former Earth and space sciences postdoctoral researcher — now a faculty member at the University of St. Andrews in Scotland — and Jonathan Zaloumis of Arizona State University.

The research was funded by grants from NASA, the UW-based and the National Science Foundation; drilling was funded by the Agouron Institute.

###

For more information, contact Koehler at koehlerm@uw.edu or Buick at 206-543-1913 or buick@ess.washington.edu.

NASA grant NNX16A137G
NSF FESD grant 338810

The amount of biomass – life – in Earth’s ancient oceans may have been limited due to low recycling of the key nutrient , according to new research by the 91̽�� and the University of St. Andrews in Scotland.

The research, published Nov. 22 in the journal Science Advances, also comments on the role of volcanism in supporting Earth’s early biosphere — and may even apply to the search for life on other worlds.

The paper’s lead author is , a 91̽��doctoral student in Earth and space sciences; coauthor is , a research fellow at the University of St. Andrews and former 91̽��postdoctoral researcher. , 91̽��professor of Earth and space sciences, advised the researchers.

Their aim, Kipp said, was to use theoretical modeling to study how ocean phosphorus levels have changed throughout Earth’s history.

“We were interested in phosphorus because it is thought to be the nutrient that limits the amount of life there is in the ocean, along with carbon and nitrogen,” said Kipp. “You change the relative amount of those and you change, basically, the amount of biological productivity.”

Kipp said their model shows the ability of phosphorus to be recycled in the ancient ocean “was much lower than today, maybe on the order of 10 times less.”

All life needs abundant food to thrive, and the chemical element phosphorus – which washes into the ocean from rivers as phosphate — is a key nutrient. Once in the ocean, phosphorus gets recycled several times as organisms such as plankton or eukaryotic algae that “eat” it are in turn consumed by other organisms.

“As these organisms use the phosphorus, they in turn get grazed upon, or they die and other bacteria decompose their organic matter,” said Kipp, “and they release some of that phosphorus back into the ocean. It actually cycles through several times,” allowing the liberated phosphorus to build up in the ocean. The amount of recycling is a key control on the amount of total phosphorus in the ocean, which in turn supports life.

Buick explained: “Every gardener knows that their plants grow only small and scraggly without phosphate fertilizer. The same applies for photosynthetic life in the oceans, where the phosphate ‘fertilizer’ comes largely from phosphorus liberated by the degradation of dead plankton.”

But all of this requires oxygen. In today’s oxygen-rich oceans, nearly all phosphorus gets recycled in this way and little falls to the ocean floor.

Several billion years ago, in the Precambrian era, however, there was little or no oxygen in the environment.

“There are some alternatives to oxygen that certain bacteria could use, said co-author Stüeken. “Some bacteria can digest food using sulfate. Others use iron oxides.” Sulfate, she said, was the most important control on phosphorus recycling in the Precambrian era.

“Our analysis shows that these alternative pathways were the dominant route of phosphorus recycling in the Precambrian, when oxygen was very low,” Stüeken said. “However, they are much less effective than digestion with oxygen, meaning that only a smaller amount of biomass could be digested. As a consequence, much less phosphorus would have been recycled, and therefore total biological productivity would have been suppressed relative to today.”

Kipp likened early Earth’s low-oxygen ocean to a kind of “canned” environment, with oxygen sealed out: “It’s a closed system. If you go back to the early Precambrian oceans, there’s not very much going on in terms of biological activity.”

Stüeken noted that volcanoes were the biggest source of sulfate in the Precambrian, unlike now, and so they were necessary for sustaining a significant biosphere by enabling phosphorus recycling.

In fact, minus such volcanic sulfate, Stüeken said, Earth’s biosphere would have been very small, and may not have survived over billions of years. The findings, then, illustrate “how strongly life is tied to fundamental geological processes such as volcanism on the early Earth,” she said.

Kipp and Stüeken’s modeling may have implications as well for the search for life beyond Earth.

Astronomers will use upcoming ground- and space-based telescopes such as the James Webb Space Telescope, set for launch in 2019, to look for the impact of a marine biosphere, as Earth has, on a planet’s atmosphere. But low phosphorus, the researchers say, could cause an inhabited world to appear uninhabited — making a sort of “false negative.”

Kipp said, “If there is less life — basically, less photosynthetic output — it’s harder to accumulate atmospheric oxygen than if you had modern phosphorus levels and production rates. This could mean that some planets might appear to be uninhabited due to their lack of oxygen, but in reality they have biospheres that are limited in extent due to low phosphorus availability.

”These ‘false negatives’ are one of the biggest challenges facing us in the search for life elsewhere,” said , 91̽��astronomy professor and principal investigator for the NASA Astrobiology Institute’s , based at the UW.

“But research on early Earth’s environments increases our chance of success by revealing processes and planetary properties that guide our search for life on nearby exoplanets.”

The work was funded by grants from NASA and the National Science Foundation.

###

For more information, contact Kipp at kipp@uw.edu, Buick at 206-543-1913 or buick@ess.washington.edu or Stüeken at
ees4@st-andrews.ac.uk.

NASA Exobiology grant NNX16AI37G to Prof. Buick.

Conditions suitable to support complex life may have developed in Earth’s oceans — and then faded — more than a billion years before life truly took hold, a new 91̽��-led study has found.

The findings, based on using the element selenium as a tool to measure oxygen in the distant past, may also benefit the search for signs of life beyond Earth.

In a paper published Jan. 18 in the Proceedings of the National Academy of Sciences, lead author , a 91̽��doctoral student in Earth and space sciences, analyzed isotopic ratios of the element selenium in sedimentary rocks to measure the presence of oxygen in Earth’s atmosphere between 2 and 2.4 billion years ago.

Kipp’s 91̽��coauthors are former Earth and space sciences postdoctoral researcher — now a faculty member at the University of St. Andrews in Scotland — and professor , who is also a faculty member with the . Their other coauthor is Andrey Bekker of the University of California, Riverside, whose original hypothesis this work helps confirm, the researchers said.

“There is fossil evidence of complex cells that go back maybe 1 ¾ billion years,” said Buick. “But the oldest fossil is not necessarily the oldest one that ever lived – because the chances of getting preserved as a fossil are pretty low.

“This research shows that there was enough oxygen in the environment to have allowed complex cells to have evolved, and to have become ecologically important, before there was fossil evidence.” He added, “That doesn’t mean that they did — but they could have.”

Kipp and Stüeken learned this by analyzing selenium traces in pieces of sedimentary shale from the particular time periods using mass spectrometry in the 91̽��Isotope Geochemistry Lab, to discover if selenium had been changed by the presence of oxygen, or oxidized. Oxidized selenium compounds can then get reduced, causing a shift in the isotopic ratios which gets recorded in the rocks. The abundance of selenium also increases in the rocks when lots of oxygen is present.

Buick said it was previously thought that oxygen on Earth had a history of “none, then some, then a lot. But what it looks like now is, there was a period of a quarter of a billion years or so where oxygen came quite high, and then sunk back down again.”

The oxygen’s persistence over a long stretch of time is an important factor, Kipp stressed: “Whereas before and after maybe there were transient environments that could have occasionally supported these organisms, to get them to evolve and be a substantial part of the ecosystem, you need oxygen to persist for a long time.”

Stüeken said such an oxygen increase has been guessed at previously, but it was unclear how widespread it was. This research creates a clearer picture of what this oxygen “overshoot” looked like: “That it was moderately significant in the atmosphere and surface ocean – but not at all in the deep ocean.”

What caused oxygen levels to soar this way only to crash just as dramatically?

“That’s the million-dollar question,” Stüeken said. “It’s unknown why it happened, and why it ended.”

“It is an unprecedented time in Earth’s history,” Buick said. “If you look at the selenium isotope record through time, it’s a unique interval. If you look before and after, everything’s different.”

The use of selenium — named after the Greek word for moon — as an effective tool to probe oxygen levels in deep time could also be helpful in the search for oxygen — and so perhaps life — beyond Earth, the researchers said.

Future generations of space-based telescopes, they note, will give astronomers information about the atmospheric composition of distant planets. Some of these could be approximately Earth-sized and potentially have appreciable atmospheric oxygen.

“The recognition of an interval in Earth’s distant past that may have had near-modern oxygen levels, but far different biological inhabitants, could mean that the remote detection of an oxygen-rich world is not necessarily proof of a complex biosphere,” Kipp said.

Buick concluded, “This is a new way of measuring oxygen in a planet’s historical past, to see whether complex life could have evolved there and persisted long enough to evolve into intelligent beings.”

The research was funded by grants from the National Science Foundation, NASA and the NASA Astrobiology Institute and Canada’s Natural Sciences and Engineering Research Council.

###

For more information, contact Buick at 206-543-1913 or buick@ess.washington.edu, Kipp at kipp@uw.edu or Stüeken at ees4@st-andrews.ac.uk.

Grant numbers: NSF #EAR-0921580, FESD #1338810, NASA #NNX16AI37G, NASA Astrobiology #NNA04CC09A.

The , published online May 9 in , reverse the commonly accepted idea that the early Earth had a thicker atmosphere to compensate for weaker sunlight. The finding also has implications for which gases were in that atmosphere, and how biology and climate worked on the early planet.

“For the longest time, people have been thinking the atmospheric pressure might have been higher back then, because the sun was fainter,” said lead author , who did the work as part of his 91̽��doctorate in Earth and space sciences. “Our result is the opposite of what we were expecting.”

The idea of using bubbles trapped in cooling lava as a “” to determine the weight of air in our planet’s youth occurred decades ago to co-author , a 91̽��professor of Earth and space sciences. Others had used the technique to measure the elevation of lavas a few million years old. To flip the idea and measure air pressure farther back in time, researchers needed a site where truly ancient lava had undisputedly formed at sea level.

Their field site in Western Australia was discovered by co-author Tim Blake of the University of Western Australia. There, the Beasley River has exposed 2.7 billion-year-old basalt lava. The lowest lava flow has “” that burrow into glassy shards, proving that molten lava plunged into seawater. The team drilled into the overlying lava flows to examine the size of the bubbles.

A stream of molten rock that forms a lava quickly cools from top and bottom, and bubbles trapped at the bottom are smaller than those at the top. The size difference records the air pressure pushing down on the lava as it cooled, 2.7 billion years ago.

Rough measurements in the field suggested a surprisingly lightweight atmosphere. More rigorous x-ray scans from several lava flows confirmed the result: The bubbles indicate that the atmospheric pressure at that time was less than half of today’s.

Earth 2.7 billion years ago was home only to single-celled microbes, sunlight was about one-fifth weaker, and the atmosphere contained no oxygen. But this finding points to conditions being even more otherworldly than previously thought. A lighter atmosphere could affect wind strength and other climate patterns, and would even alter the boiling point of liquids.

“We’re still coming to grips with the magnitude of this,” Buick said. “It’s going to take us a while to digest all the possible consequences.”

Other geological evidence clearly shows liquid water on Earth at that time, so the early atmosphere must have contained more heat-trapping greenhouse gases, like methane and carbon dioxide, and less nitrogen.

The new study is an advance on the 91̽��team’s previous work on “” that first cast doubt on the idea of a far thicker ancient atmosphere. The result also reinforces Buick’s 2015 finding that out of Earth’s atmosphere some 3 billion years ago.

“The levels of nitrogen gas have varied through Earth’s history, at least in Earth’s early history, in ways that people just haven’t even thought of before,” said co-author , a 91̽��professor of Earth and space sciences. “People will need to rewrite the textbooks.”

The researchers will next look for other suitable rocks to confirm the findings and learn how atmospheric pressure might have varied through time.

While clues to the early Earth are scarce, it is still easier to study than planets outside our solar system, so this will help understand possible conditions and life on other planets where atmospheres might be thin and oxygen-free, like that of the early Earth.

Som is CEO of Seattle-based , a nonprofit that focuses on interdisciplinary space science research, international awareness, science education and public outreach. He currently does astrobiology research at NASA’s Ames Research Center in California.

The research was funded by NASA. Other co-authors are former 91̽��undergraduate student John Perreault, now at the University of Alaska Fairbanks; former 91̽��graduate student , now at Scotland’s James Hutton Institute; and , curator of geology at the Denver Museum of Nature & Science.

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For more information, contact Som at 650-604-1483 or sanjoy@bmsis.org, Buick at 206-543-1913 or buick@uw.edu and Catling at 206-543-8653 or dcatling@uw.edu.

Grants: NNX08AP56G and NNA13AA93A

But what happened next? Life can exist without oxygen, but without plentiful nitrogen to build genes – essential to viruses, bacteria and all other organisms – life on the early Earth would have been scarce.

The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago. Now research from the 91̽�� looking at some of the planet’s oldest rocks finds evidence that 3.2 billion years ago, life was already pulling nitrogen out of the air and converting it into a form that could support larger communities.

“People always had the idea that the really ancient biosphere was just tenuously clinging on to this inhospitable planet, and it wasn’t until the emergence of nitrogen fixation that suddenly the biosphere become large and robust and diverse,” said co-author , a 91̽��professor of Earth and space sciences. “Our work shows that there was no nitrogen crisis on the early Earth, and therefore it could have supported a fairly large and diverse biosphere.”

The were published Feb. 16 in Nature.

The authors analyzed 52 samples ranging in age from 2.75 to 3.2 billion years old, collected in South Africa and northwestern Australia. These are some of the oldest and best-preserved rocks on the planet. The rocks were formed from sediment deposited on , so are free of chemical irregularities that would occur near a subsea volcano. They also formed before the atmosphere gained oxygen, roughly 2.3 to 2.4 billion years ago, and so preserve chemical clues that have disappeared in modern rocks.

Even the oldest samples, 3.2 billion years old – three-quarters of the way back to the birth of the planet – showed chemical evidence that life was pulling nitrogen out of the air. The ratio of heavier to lighter nitrogen atoms fits the pattern of nitrogen-fixing enzymes contained in single-celled organisms, and does not match any chemical reactions that occur in the absence of life.

“Imagining that this really complicated process is so old, and has operated in the same way for 3.2 billion years, I think is fascinating,” said lead author , who did the work as part of her 91̽��doctoral research. “It suggests that these really complicated enzymes apparently formed really early, so maybe it’s not so difficult for these enzymes to evolve.”

Genetic analysis of nitrogen-fixing enzymes have placed their origin at between 1.5 and 2.2 billion years ago.

“This is hard evidence that pushes it back a further billion years,” Buick said.

Fixing nitrogen means breaking a tenacious triple bond that holds nitrogen atoms in pairs in the atmosphere and joining a single nitrogen to a molecule that is easier for living things to use. The chemical signature of the rocks suggests that nitrogen was being broken by an enzyme based on , the most common of the three types of nitrogen-fixing enzymes that exist now. Molybdenum is now abundant because oxygen reacts with rocks to wash it into the ocean, but its source on the ancient Earth – before the atmosphere contained oxygen to weather rocks – is more mysterious.

The authors hypothesize that this may be further evidence that some early life may have existed in single-celled layers on land, exhaling small amounts of oxygen that reacted with the rock to release molybdenum to the water.

“We’ll never find any direct evidence of land scum one cell thick, but this might be giving us indirect evidence that the land was inhabited,” Buick said. “Microbes could have crawled out of the ocean and lived in a slime layer on the rocks on land, even before 3.2 billion years ago.”

Future work will look at what else could have limited the growth of life on the early Earth. Stüeken has begun a 91̽��postdoctoral position funded by NASA to look at trace metals such as zinc, copper and cobalt to see if one of them controlled the growth of ancient life.

Other co-authors are at the University of Johannesburg in South Africa, who provided some samples from gold mines, and 91̽��graduate student . The research was funded by NASA, the UW’s , the and the .

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For more information, contact Buick at 206-543-1913 or buick@uw.edu and Stüeken at evast@uw.edu.