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From what I understand the 'Great Oxidation Event' occurred around 2.4 billion - 2.3 billion years ago, when cyanobacteria flooded Earth's atmosphere with oxygen.
The 'boring billion' period was around 1.8 billion years ago, during which it is thought not a lot changed on planet Earth. Low oxygen levels were thought to be 1-40% of modern oxygen levels during this time.
Why did the atmosphere go from 'flooded with oxygen' to 1-40% of modern oxygen levels. Was it because during the Mesoproterozoic era, the rate of burial of decaying organic carbon matter under marine sediments flatlined?
Your question probably arises from a misunderstanding regarding the 'flooding' metaphor. I would not assume that 'flooded Earth's atmosphere with oxygen' means a lot of oxygen in the first place… the metaphor means that oxygen levels rose from basically absent to noticeable.
If you look at the history of oxygen in Earth's atmosphere you see a general trend of gradual increase with a 1GY lasting stationary phase (Holland (2006), picture taken from above linked Wikipedia article - red and green lines are upper and lower estimates, respectively):
After initial atmospheric oxygenation about 2.5 GYa, Earth's oxygen sinks (mainly the oceans, after that landmasses and the ozone layer) were filled and buffered atmospheric oxygen levels, keeping them low. Once those sinks were saturated (approx. 850 MYa), the atmosphere started to oxygenise rapidly.
The constant (or as discussed below: drop in) oxygen concentration is caused by these sinks. The oxygen that is produced by photosynthesis was just not available to Earth's organisms as it was not atmospheric.
As @GerardoFurtado points out in the comment, modalities of the stationary phase are still debated. A review by Lyons et al. (2014) presents evidence that after the initial increase in oxygen levels, a drop in atmospheric oxygen preceded the stationary phase (see their Fig. 1, blue boxes). This does not change much as the newly inferred stationary phase, though probably a more fluctuating stationary phase than suggested by Holland (2006), is still higher than before the great oxidation event and lower than at present.
The major conclusions remains the same: There is evidence that the seemingly slow evolution 2-1 GYa was probably caused by oxygen limitation and oxygen levels were buffered by oxygen sinks. The change of oxygen concentration was determined by both the rate of oxygen production and the rate with which oxygen is stored in those sinks; the interplay of those rates caused the oxygen concentration to remain constant, drop or occasionally even rise, i.e. fluctuated.
Maybe the introduction of any amount of oxygen altered the availability of nutrients. The oxygen producers had evolved in low / no oxygen conditions and it was only when they reached critical mass that the great oxygenation event could occur.
Once it did occur, nutrients that had once been soluble and available were in short supply: specifically iron and reduced nitrogen.
Fe2+ is soluble and so before the oxygenation event there was probably a fair bit sloshing around. Once oxygen came the iron turned to Fe3+ and was much harder to come by. https://www.princeton.edu/~cebic/ironIIvsIII.html
Iron is still growth limiting in large areas of open ocean, as evidenced by this experiment supplementing the open ocean with iron. http://www.nytimes.com/2012/10/19/science/earth/iron-dumping-experiment-in-pacific-alarms-marine-experts.html
Nitrogen is the other nutrient whose availability would have changed.
The ancient enzyme used by nitrogen fixers is poisoned by oxygen and once oxygen was around, the activity of these organisms no doubt plummetted and with it, availability of reduced nitrogen. Lack of iron would be a double whammy for the nitrogen fixers in which the enzyme requires iron.
So: maybe the boring billion occurred because oxygen-induced nutrient starvation handicapped proliferation of organisms, and with low proliferation you have fewer chances to evolve something new.
Snowball's chance in Earth and early signs of life
DNDXCB View of Earth 650 million years ago during the Marinoan glaciation. Credit: University of St Andrews
New research led by the University of St Andrews helps answer one of the most asked questions in geoscience, when did Earth start to become habitable to complex life?
The research, led by the School of Earth and Environmental Sciences, and published in the journal Proceedings of the National Academy of Sciences (PNAS) today addresses this by defining which came first, the Great Oxidation Event (GOE) or the Paleoproterozoic snowball Earth period. The relative timing of these global events is pivotal to understanding changes in atmospheric composition and climate conditions, and how the first signs of life on Earth began.
Early in Earth's history the atmosphere lacked oxygen and as such would have been hostile to much of the life that covers the planet today. For over half a century, geoscientists have been trying to pinpoint exactly when atmospheric oxygen levels started to rise thereby allowing Earth to become more habitable for complex, multicellular life. Scientific consensus has been that the first notable rise in oxygen occurred during the Great Oxidation Event (GOE), sometime between 2.4 and 2.3 billion years ago.
Associated with this GOE, rocks from Canada, South Africa, Russia and elsewhere show that a major global glaciation took place. Geological evidence suggests that ice sheets extended to the tropics in what has been termed a 'snowball Earth' event. What has remained unclear though is the relative timing of these events.
The team of researchers focussed on defining the timing of the GOE by examining a set of drill-cores from north-west Russia (Fennoscandia), gathered as part of the international FAR-DEEP drilling program. The scientists studied two rock formations, the older Seidorechka Sedimentary Formation and the younger Polisarka Sedimentary Formation.
The team conducted sulfur isotope analysis to determine what the oxygen content of the atmosphere was likely to have been at the time each rock succession was deposited. This required the development of a new analytical technique capable of analyzing, with high precision, all four stable isotopes of sulfur. As a result, the University of St Andrews now has the only laboratory in the UK with this capability and only the second lab in the world to develop this particular method.
Changes in the relative amounts of each sulfur isotope in the samples allowed the team to identify whether the sulfur isotopes in these rocks follow a predictable ratio, mass-dependent fractionation or MDF, or whether they fail to follow a predictable ratio, indicating mass-independent fractionation or MIF. It is only possible to produce and preserve sulfur MIF in an atmosphere lacking significant oxygen when oxygen levels rise, sulfur MDF takes over. Therefore, a common marker for the GOE is this transition from MIF to MDF in the rock record.More than 250 m of drill core was examined at the Geological Survey of Norway repository in Trondheim, Norway. Credit: Matthew Robert Warke
The analysis found that the older Seidorechka Sedimentary Formation preserves sulfur MIF but the younger Polisarka Sedimentary Formation preserves sulfur MDF conditions. This means that the GOE occurred sometime between the deposition of these two rock successions. Using previously published age constraints, the researchers concluded that the GOE must have occurred between 2.50 and 2.43 billion years ago. This is an older age for the GOE which was previously thought to have occurred 2.48 to 2.39 billion years ago and constrains a narrower, approximately 70 million-year time interval in which it could have occurred.
Lead scientist, Dr. Matthew Warke, from the School of Earth and Environmental Sciences, said: "Our research allows us to say definitively that the GOE preceded the earliest snowball Earth glaciation in history as the latter is thought to have occurred around 2.42 billion years ago. This raises the possibility that the rise of oxygen in Earth's atmosphere during the GOE may have triggered one of the most severe glaciations the planet ever experienced.
"One possible mechanism by which this may have happened, that is consistent with our results and current thinking, is that rising atmospheric oxygen levels may have critically destabilized a methane-dominated greenhouse causing surface temperatures to fall rapidly. Other mechanisms may have operated, but crucially our results rule out any mechanisms that invoke that the snowball glaciation occurred prior to the GOE, resolving one of the most long-standing 'chicken or egg' problems in Earth history."
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Why Did Earth Have a Poison-Filled "Boring Billion" Years?
Almost 2 billion years ago, evolution came down with a puzzling case of the blahs. For roughly an eon, life on Earth changed but little, dominated by hardy microbes in oceans starved of oxygen. The sheer monotony of the geologic record for this period inspired scientists to nickname it the Boring Billion. The moniker is unfair, says Andrew Knoll , professor of natural history and of Earth and planetary sciences at Harvard University.
During the Boring Billion, the planet’s oceans were light on oxygen and heavy on toxic hydrogen sulfide. What was life like under such harsh conditions?
Most of the biomass in the oceans would have been bacteria and archaea [another type of microbial organism that often inhabits extreme environments]. This was probably the golden age for bacteria that photosynthesize in the absence of oxygen, using hydrogen sulfide rather than water. Some of the bacteria were single-celled some were multicellular filaments or sheets. We also have evidence of microbial mats. You just had slime over the seafloor. In this interval we start having fossil evidence of eukaryotic organisms—things with a cell nucleus, like us. But there’s not a great diversity of them. Eukaryotes are, at best, playing a rather limited role.
How did the planet get this way?
During the first 2 billion years of Earth’s history, there was no oxygen in the atmosphere or oceans. That began to change about 2.4 billion years ago. The best idea, from Don Canfield [of the University of Southern Denmark], is that building up a little bit of atmospheric oxygen causes iron pyrite minerals in the continents to oxidize and form sulfate. Rivers carry sulfate into the ocean, where certain bacteria convert it into hydrogen sulfide.
By about 1.8 billion years ago, we start seeing oceans in which the surface had a little bit of oxygen, but just beneath the surface you would regularly encounter sulfide but no oxygen. Along with my colleagues Dave Johnston and Ann Pearson at Harvard and NASA’s Felisa Wolfe-Simon , I hypothesize that biological feedback cycles, including one involving sulfide-based photosynthesis, would tend to maintain this world in which oxygen levels remain low and sulfide high [for the next “boring” billion years]. During this time, bacteria that can use hydrogen sulfide for photosynthesis are as happy as clams. But sulfide is generally toxic to eukaryotes—most of which have mitochondria [the structures inside cells that produce energy]—because it inhibits their ability to respire. So those conditions could have put a brake on the expansion of eukaryotic cells.
How do you even know what was living so long ago?
You look for rocks of appropriate age, which we can determine by measuring radioactive uranium isotopes and their products in the volcanic rocks interspersed with them, and study their composition. There you can find actual body fossils, which can be preserved beautifully. There are also organic molecules preserved in sedimentary rocks. DNA and proteins don’t preserve very well, but lipids [fatty molecules] do, and we can identify different organisms through characteristic lipids. We also look for fossils of structures called stromatolites , which are reefs built by microbial communities. Those tell us a great deal about the distribution of life on the seafloors.
If the conditions were so great for sulfur-loving bacteria back then, why didn’t they evolve greater complexity?
Prokaryotic organisms—bacteria, archaea—probably lack the genetic makeup to do that. Eukaryotic cells have a very sophisticated pattern of gene regulation, much more complicated than the comparable system in bacteria. It allows eukaryotic cells to evolve into multicellular organisms that have remarkable structural and functional variation. Bacteria have been around for something close to 4 billion years and yet have never evolved multicellular complexity that comes anywhere close to what eukaryotes have evolved—nothing like even a sponge, let alone a human being.
How can you verify your picture of life during the Boring Billion?
The idea that sulfide-based photosynthesis was important during the Boring Billion is based on one limited data set from drill cores in northern Australia showing pigment molecules associated with sulfide-using bacteria. We predict that when people do a more thorough job of evaluating the organic matter in rocks of this age, they will see a wider distribution of these molecular fossils.
After so many years of stagnation, how did evolution get going again?
A lot of people think that tectonics is what bumped life into a different world. You see some tectonic change during the Boring Billion, but you don’t have the kind of wholesale continental collisions you have both before it starts and just when it ends. That continental breakup may have been accompanied by a great increase in hydrothermal vent activity, which produces large amounts of iron. If sulfide-rich subsurface waters posed a continuing challenge to eukaryotic organisms, the shift to iron-rich subsurface waters would have removed this challenge.
As the Boring Billion closes, things really happen. Geochemical evidence shows that we begin losing sulfidic waters about 800 million years ago. At the same time, paleontology tells us that eukaryotes are diversifying and expanding over large areas of the ocean. Molecular evidence suggests that animals start to differentiate around then.
There are now major fluctuations in the carbon cycle never before seen. We have multiple glaciations , of which at least two seem to have pretty much covered the world. And we have oxygen rise, so that we come to have a world much more like the world that we know. The 300 million years after the end of the Boring Billion are probably the most eventful 300 million years in our planet’s history.
So you would say that calling it the Boring Billion sells this period short?
Very much so. One reason is that understanding the interval’s stability may be more of a challenge than understanding the change we see both before and after. And we know it wasn’t that evolution stopped. In fact, there’s reason to believe that all of the properties of cell biology that made complex life possible in the next geologic era were put in place here: cytoskeletons that allow eukaryotic cells to change shape, and cell polarity that allows cells to send a molecular message to one side of the cell but not the other, and to interact with nearby cells. The molecular circuitry and cross talk that allow complex organisms like us to exist today all took root in the so-called Boring Billion.
You recently showed that the oceans had an abundance of sulfide and a dearth of oxygen during a later period as well, around 500 million years ago. Evolution slowed down then, too. Is this a regular pattern?
Yes, but it is less and less frequent. If you look at the last 65 million years, in the so-called Cenozoic era, I don’t think there are any examples of globally widespread subsurface oxygen depletion. In the previous era, the Mesozoic, from 65 to 250 million years ago, there were six or seven such oceanic anoxic events. They were short, sharp shocks. Going back even farther, in the Proterozoic, these kinds of environments were everywhere. Over the course of time, it goes from being ubiquitous to repetitive to rare to absent—more evidence that we live at an unusual time in the history of Earth.
You are a member of the Mars Rover science team. What parallels do you see between the geologic history of Earth and Mars?
We can apply what we’ve learned about studying ancient rocks on Earth to Mars. NASA’s Mars Exploration Rovers have enabled us to examine 3.5- to 4-billion-year-old sedimentary rocks on Mars, in much the same way that we study ancient strata on Earth. We’ve learned that liquid water was present on the Martian surface during this interval, but also that its chemical makeup and short duration would have challenged any known life-forms. Mars was wetter very early in its history, but the probability that it was ever a blue planet like the Earth is, I think, remote. The more we learn about Mars, the more it seems to me a planet that’s very different from Earth.
The essential trace elements
Bio-essential trace elements are critical to life and evolution. These include cobalt, selenium, copper, zinc, molybdenum, vanadium and cadmium. Certain species need these trace elements to survive.
The elements are linked into the chemical structure of the cells and become a natural nutrient for survival. Cobalt is a central atom in the structure of vitamin B12, whereas zinc is essential for growth in many species.
The UTAS research team showed that at certain periods of earth history these trace elements were in short supply (such as the boring billion period) leading to evolutionary decline, whereas in other periods the bio-essential elements were in great abundance, causing rapid evolutionary change.
Earth’s Permanent Oxygen Rise Occurred 100 Million Years Later Than Thought
The permanent rise of oxygen in the Earth’s atmosphere, which fundamentally changed the subsequent nature of Earth’s habitability, occurred much later than thought, according to new research.
And the study, from an international team led by the University of Leeds and including researchers from the University of California-Riverside, Harvard University, the University of Southern Denmark, and the University of St Andrews, also provides an explanation for some of the most extreme climate episodes to have affected the Earth, when the planet was repeatedly covered with ice.
“Now at last we have that piece of the puzzle.” — Professor Simon Poulton, Chair in Biogeochemistry and Earth History
The first time oxygen was significantly present in the atmosphere was about 2.43 billion years ago, and this marks the start of the Great Oxidation Event — a pivotal period in Earth’s history.
Although the Great Oxidation Event led to oxygen levels that were still much lower than today, it dramatically changed the chemical composition of the planet’s surface and set the stage for the subsequent course of biological evolution on Earth, which ultimately led to a planet teeming with animal life.
By analyzing rocks from South Africa, which were deposited in the ocean at the time of the Great Oxidation Event, the researchers discovered that early atmospheric oxygenation was short-lived, and oxygen did not become a permanent feature of the atmosphere until much later.
Professor Simon Poulton, of Leeds’ School of Earth and Environment, led the research.
He said: “The Great Oxidation Event fundamentally changed Earth’s environment and habitability. This early period of oxygenation was thought to have occurred between about 2.43 and 2.32 billion years ago.
“However, our research shows that, in fact, oxygenation of the atmosphere was highly unstable over a period of about 200 million years, with permanent atmospheric oxygenation occurring about 100 million years later than previously thought.”
Their findings, published in the journal Nature, also suggest a direct link between fluctuations in atmospheric oxygen concentration and greenhouse gas concentrations.
Professor Andrey Bekker of the University of California-Riverside, who co-authored the study, said: “These findings help explain four widespread glaciations that occurred coincident with the Great Oxidation Event, some of which were likely to have covered the whole of the Earth in ice for millions of years.
“Our new data show that the permanent rise of oxygen actually occurred after the final major glaciation of the period and not before it, which had previously been a major puzzle in our understanding of links between early atmospheric oxygenation and intense climatic instability.”
The research team has re-labeled this period the Great Oxidation Episode. It ushered in a 1.5 billion year period of subsequent climatic and environmental stability, which remained until a second major period of rising oxygen and climate instability at the end of the Precambrian period.
Professor David Johnston, a co-author from Harvard University said: “The rise of atmospheric oxygen was a key factor in Earth’s habitability.
“Unravelling the history of atmospheric oxygenation ultimately allows us to understand how oxygen rose to levels that were sufficient to allow the evolution of animals.
“The Great Oxidation Episode, when atmospheric oxygen first rose to appreciable levels, represents a pivotal step in this history.”
Professor Poulton added: “We cannot begin to understand the causes and consequences of atmospheric oxygenation, the most significant control on Earth’s habitability, if we do not know when permanent atmospheric oxygenation actually occurred. Now at last we have that piece of the puzzle.”
Reference: “A 200-million-year delay in permanent atmospheric oxygenation” by Simon W. Poulton, Andrey Bekker, Vivien M. Cumming, Aubrey L. Zerkle, Donald E. Canfield and David T. Johnston, 29 March 2021, Nature.
The research team included Simon Poulton, University of Leeds Andrey Bekker, University of California-Riverside David Johnston and Vivien Cumming, Harvard University Donald Canfield, University of Southern Denmark Aubrey Zerkle, University of St Andrews.
The research team received funding from the Royal Society, the Leverhulme Trust and NASA.
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6 Comments on "Earth’s Permanent Oxygen Rise Occurred 100 Million Years Later Than Thought"
“Our new data show that the permanent rise of oxygen actually occurred after the final major glaciation of the period and not before it, …”
If the oxygen came from photosynthesizing cyanobacteria, which wasn’t possible during the ‘Icehouse’ conditions preceding the Great Oxygen Event, what caused the end of world-wide glaciation? If the end was caused by the buildup of volcanogenic CO2, why didn’t Earth plunge back into another ‘Icehouse’ state as soon as the cyanobacteria drew down the CO2 in the process of making oxygen?
I don’t think anybody knows, but if the new time evolution is independently veriified scientists should be able to asemble more data on mechanisms.
Meanwhile I found an article covering their early hypotheses [ https://www.sciencealert.com/scientists-say-earth-nearly-lost-all-its-oxygen-2-3-billion-years-ago ]. The final discussion is long, convoluted, lack data and makes fuzzy claims, but that is the nature or many early hypotheses. I would be curious how they mean the biosphere accumulated the nutrients, but maybe the populations increased over time, especially since the Great Oxygenation Event resulted in the worst mass extinction we know of – an estimate 99+ % of species became extinct, including among the cyanobacteria. (We still haven’t found much of any of their older stem lineages, IIRC.) So FWIW:
“They found that after the third glaciation event the atmosphere was oxygen-free at first, then oxygen rose and dropped again. Oxygen rose again 2.32 billion years ago – the point at which scientists previously thought the rise was permanent. But in the younger rocks, Bekker and his colleagues again detected a drop in oxygen levels. This drop coincided with the final glaciation, the one that hadn’t previously been linked to atmospheric changes.
“Atmospheric oxygen during this early time was very unstable and it went up to relatively high levels and it fell down to very low levels,” Bekker said. “That’s something we didn’t expect until maybe the last 4 or 5 years [of research].”
Cyanobacteria vs. volcanoes
Researchers are still working out what caused all these fluctuations, but they have some ideas. One key factor is methane, a greenhouse gas that’s more efficient at trapping heat than carbon dioxide.
Today, methane plays a small role in global warming compared with carbon dioxide, because methane reacts with oxygen and disappears from the atmosphere within about a decade, whereas carbon dioxide sticks around for hundreds of years. But when there was little to no oxygen in the atmosphere, methane lasted a lot longer and acted as a more important greenhouse gas.
So the sequence of oxygenation and climate change possibly went something like this: Cyanobacteria began producing oxygen, which reacted with the methane in the atmosphere at the time, leaving only carbon dioxide behind.
This carbon dioxide wasn’t abundant enough to make up for the warming effect of the lost methane, so the planet started to cool. The glaciers expanded, and the surface of the planet became icy and cold.
Saving the planet from a permanent deep-freeze, though, were subglacial volcanoes. Volcanic activity eventually boosted carbon dioxide levels high enough to warm the planet again. And while oxygen production lagged in the ice-covered oceans due to the cyanobacteria receiving less sunlight, methane from volcanoes and microorganisms again began to build up in the atmosphere, further heating things up.
But volcanic carbon dioxide levels had another major effect. When carbon dioxide reacts with rainwater, it forms carbonic acid, which dissolves rocks more quickly than pH-neutral rainwater. This faster weathering of rocks brings more nutrients such as phosphorus into the oceans.
More than 2 billion years ago, such a nutrient influx would have driven the oxygen-producing marine cyanobacteria into a productive frenzy, again boosting atmospheric oxygen levels, driving down methane and starting the whole cycle again.
Eventually, another geological change broke this oxygenation-glaciation cycle. The pattern seems to have ended about 2.2 billion years ago when the rock record indicates an increase in organic carbon being buried, which suggests that photosynthetic organisms were having a heyday.
No one knows exactly what triggered this tipping point, though Bekker and his colleagues hypothesize that volcanic activity in this period provided a new influx of nutrients to the oceans, finally giving cyanobacteria everything they needed to thrive.
At this point, Bekker said, oxygen levels were high enough to permanently suppress methane’s oversized influence on the climate, and carbon dioxide from volcanic activity and other sources became the dominant greenhouse gas for keeping the planet warm.”
Earth Had Oxygen Much Earlier Than Thought
Oxygen may have filled Earth's atmosphere hundreds of millions of years earlier than previously thought, suggesting that sunlight-dependent life akin to modern plants evolved very early in Earth's history, a new study finds.
The findings, detailed in the Sept. 26 issue of the journal Nature,have implications for extraterrestrial life as well, hinting that oxygen-generating life could arise very early in a planet's history and potentially suggesting even more worlds could be inhabited around the universe than previously thought, the study's authors said.
It was once widely assumed that oxygen levels remained low in the atmosphere for about the first 2 billion years of Earth's 4.5-billion-year history. Scientists thought the first time oxygen suffused the atmosphere for any major length of time was about 2.3 billion years ago in what is called the Great Oxidation Event. This jump in oxygen levels was almost certainly due to cyanobacteria &mdash microbes that, like plants, photosynthesize and exhale oxygen.
However, recent research examining ancient rock deposits had suggested that oxygen may have transiently existed in the atmosphere 2.6 billion to 2.7 billion years ago.
The new study pushes this boundary back even further, suggesting Earth's atmosphere became oxygenated about 3 billion years ago, more than 600 million years before the Great Oxidation Event. In turn, this suggests that something was around on the planet to put that oxygen in the atmosphere at this time.
"The fact oxygen is there requires oxygenic photosynthesis, a very complex metabolic pathway, very early in Earth's history," said researcher Sean Crowe, a biogeochemist at the University of British Columbia in Vancouver. "That tells us it doesn't take long for biology to evolve very complex metabolic capabilities." [7 Theories on the Origin of Life]
Ancient oxygen reactions
Crowe and his colleagues analyzed levels of chromium and other metals in samples from South Africa that could serve as markers of reactions between atmospheric oxygen and minerals in Earth's rocks. They looked at both samples of ancient soil and marine sediments from about the same time period &mdash 3 billion years ago.
The researchers focused on the different levels of chromium isotopeswithin their samples. Isotopes are variants of elements all isotopes of an element have the same number of protons in their atoms, but each has a different number of neutrons &mdash for instance, each atom of chromium-52 has 28 neutrons, while atoms of chromium-53 have 29.
When atmospheric oxygen reacts with rock &mdash a process known as weathering &mdashheavier chromium isotopes, such as chromium-53, often get washed out to sea by rivers. This means heavier chromium isotopes are often depleted from soils on land and enriched in sediments in the ocean when oxygen is around. These proportions of heavier chromium were just what were seen in the South African samples. Similar results were seen with other metals, such as uranium and iron, that hint at the presence of oxygen in the atmosphere.
"We now have the chemical tools to detect trace atmospheric gases billions of years ago," Crowe told LiveScience.
'Almost certainly biological'
All in all, the researchers suggest atmospheric oxygen levels 3 billion years ago were about 100,000 times higher than what can be explained by regular chemical reactions in Earth's atmosphere. "That suggests the source of this oxygen was almost certainly biological," Crowe said.
"It's exciting that it took a relatively short time for oxygenic photosynthesis to evolve on Earth," Crowe added. "It means that it could happen on other planets on Earth, expanding the number of worlds that could've developed oxygenated atmospheres and complex oxygen-breathing life."
Future research can look for similarly aged rocks from other places, both on and outside Earth, to confirm these findings. "Research could also look at earlier rocks," Crowe said. "Chances are, if there was oxygen 3 billion years ago, there was likely oxygen production some time before as well. How far back does it go?"
The Biology Behind Banded Iron Formations
A long-enduring puzzle in the evolution of the early Earth concerns when and to what extent surface oxidation occurred. One important piece of this puzzle is determining when oxygen production began, and how early oxygen was consumed by reduced species, such as iron (Fe(II)), in the oceans. One way of tracing the Fe redox cycle through time has been studying banded iron formations ( BIF s). These rock formations likely formed when Fe(II)-rich hydrothermal fluid wells up into shallow water. Fe(II) then undergoes oxidation, resulting in layers of rock that contain evidence of how and when the process happened.
It is thought that oxygen did not make up a significant portion of the atmosphere until after the ‘Great Oxidation Event,’ roughly 2.45 billion years ago. How and when oxygen was first produced on Earth before this dramatic event is still a big question. Astrobiologists, supported in part by the NAI , are now helping to solve the mystery.
The team studied BIF s in the Isua Supracrustal Belt of southwestern West Greenland. The rocks of this formation can be 3.7-3.8 billion years old, and include the oldest known BIF s on Earth. Ultimately, the isotopic signatures in the rocks suggested that oxidation of Fe(II) was most likely the result of anoxygenic photosynthesis (i.e. photosynthesis that doesn’t produce oxygen). This supports the idea that anoxygenic photosynthesis evolved before the oxygenic photosynthesis we’re all familiar with today (and which plays an important role in keeping the atmosphere breathable for us).
The research was published in the journal Earth and Planetary Science Letters. Funding came from the NSF and NASA .
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The Story of Earth : The First 4.5 Billion Years, from Stardust to Living Planet
Hailed by The New York Times for writing "with wonderful clarity about science . . . that effortlessly teaches as it zips along," nationally bestselling author Robert M. Hazen offers a radical new approach to Earth history in this intertwined tale of the planet's living and nonliving spheres. With an astrobiologist's imagination, a historian's perspective, and a naturalist's eye, Hazen calls upon twenty-first-century discoveries that have revolutionized geology and enabled scientists to envision Earth's many iterations in vivid detail--from the mile-high lava tides of its infancy to the early organisms responsible for more than two-thirds of the mineral varieties beneath our feet. Lucid, controversial, and on the cutting edge of its field, The Story of Earth is popular science of the highest order.
"A sweeping rip-roaring yarn of immense scope, from the birth of the elements in the stars to meditations on the future habitability of our world." -Science
Earth's history: The Great Oxidation Event and the 'Boring Billion' - Biology
Earth's oxygen will last another billion years
A new study calculates how long Earth's oxygen-rich atmosphere will persist, with a most likely timeframe of 1.08 billion years until the planet is rendered uninhabitable for most life.
Credit: NASA/Goddard Space Flight Center/Francis Reddy
Today, Earth is a highly oxygenated planet – from the atmosphere, down to the lowest depths of the oceans, it demonstrates all the hallmarks of an active photosynthetic biosphere. However, the long-term timeline for Earth's atmosphere remains uncertain, particularly for the very distant future. Solving this question has great ramifications not only for the future of Earth's biosphere but for the search for life on Earth-like exoplanets beyond our Solar System.
Most scientists agree that our Sun will expand into a red giant about five billion years from now. Long before it reaches that stage, however, its ballooning size will create hellish conditions on Earth. Among the many changes to our home planet will be a gradual decline in oxygen levels. Exactly when and how this occurs has been the subject of much debate.
A new study, published this month in Nature Geoscience, tackles this problem using a numerical model of biogeochemistry and climate to reveal that the future lifespan of Earth's oxygen-rich atmosphere is just over a billion years.
"For many years, the lifespan of Earth's biosphere has been discussed based on scientific knowledge about the steady brightening of the Sun and global carbonate-silicate geochemical cycle," says Kazumi Ozaki, Assistant Professor at Toho University, Japan. "One of the corollaries of such a theoretical framework is a continuous decline in atmospheric CO2 levels and global warming on geological timescales. Indeed, it is generally thought that Earth's biosphere will come to an end in the next two billion years due to the combination of overheating and CO2 scarcity for photosynthesis. If true, one can expect that atmospheric O2 levels will also eventually decrease in the distant future. However, it remains unclear exactly when and how this will occur."
To examine how the Earth's atmosphere will evolve in the future, Ozaki and Christopher Reinhard, Associate Professor at Georgia Institute of Technology, constructed an Earth system model which simulates climate and biogeochemical processes. Because modelling future Earth evolution intrinsically has uncertainties in geological and biological evolutions, they adopted a stochastic approach, enabling the researchers to obtain a probabilistic assessment of an oxygenated atmosphere's lifespan.
Oxygen (O2), methane (CH4) and carbon dioxide (CO2) concentrations on Earth, from 500 million years ago, through to 2 billion years from now. Credit: K Ozaki/C Reinhard.
Ozaki ran the simulation more than 400,000 times – varying the model parameters – and found that Earth's oxygen-rich atmosphere will most likely persist for another 1.08 billion years. After that point, rapid deoxygenation will make the atmosphere reminiscent of the early Earth before its Great Oxidation Event around 2.5 billion years ago.
"The atmosphere after the great deoxygenation is characterised by an elevated methane, low levels of CO2, and no ozone layer. The Earth system will probably be a world of anaerobic life forms," explains Ozaki.
During its long history, our planet has seen varying levels of oxygen. Following the Great Oxidation Event of 2.4–2.0 Ga (billion years ago), it remained at a low and stable concentration before rising sharply during the Ediacaran Period (635–541 Mya) and then slowing in the Cambrian (541–485 Mya).
As a percentage of the atmosphere, oxygen reached its highest levels in the Carboniferous, peaking at 35%. This enabled many insects, which breathe through their skins, to grow to gigantic sizes. It also fuelled wildfire activity. Since then, oxygen levels have fallen and rebounded again, and today stand at roughly 20%.
Meganisopteran, the largest insects that ever lived. Credit: GermanOle, CC BY-SA 3.0, via Wikimedia Commons
Earth's oxygen-rich atmosphere today represents an important sign of life that can be remotely detectable. However, this study concludes that it will enter a relatively rapid and terminal decline at some point, and suggests that rich concentrations of the gas might only be possible for 20–30% of Earth's entire history as an inhabited planet.
Oxygen (and the photochemical by-product, ozone) is the most compelling biosignature in the search for life on exoplanets. If we can generalise these insights to Earth-like planets, then scientists need to consider additional biosignatures applicable to weakly-oxygenated and anoxic worlds, according to study authors Reinhard and Ozaki.
The image of Earth as a dying planet, with only a handful of microscopic anaerobes clinging to survival, is a depressing contrast to the rich biodiversity we see around us today. This assumes, of course, that humanity or its descendants will be unable to save Earth via technological means, such as incremental shifting of the planet's orbit to match the retreating Goldilocks zone. The expanding Sun might also make Mars more habitable.
Then again, the sheer length of time involved in this process would provide ample opportunity for Earth's remaining inhabitants to develop interstellar travel and leave the Solar System entirely to settle new systems. Our species by then might even have evolved into beings of pure energy, able to traverse dimensions and into other universes. Perhaps the Earth by then could be left as a kind of galactic relic – a monument to our ancient past.