“Oxygen flooded into the atmosphere as a pollutant, even a poison, until natural selection shaped living things to thrive on the stuff and, indeed, suffocate without it,” wrote evolutionary biologist, Richard Dawkins, in The Evidence for Evolution is the Greatest Show on Earth.
“In evolution, things always start small.”
“In evolution, things always start small,” says lead author Greg Fournier, associate professor of geobiology in MIT’s Department of Earth, Atmospheric and Planetary Sciences referring to the Great Oxidation Event, the evolutionary moment that made it possible for oxygen to eventually accumulate in the atmosphere and oceans, setting off a domino effect of diversification and shaping the uniquely habitable planet we know today. Fournier’s seminal paper sheds light on Earth’s oxygenation history by bridging the fossil record with genomic data, including horizontal gene transfers. “Even though there’s evidence for early oxygenic photosynthesis — which is the single most important and really amazing evolutionary innovation on Earth — it still took hundreds of millions of years for it to take off.”
Even though there’s evidence for early oxygenic photosynthesis — which is the single most important and really amazing evolutionary innovation on Earth — it still took hundreds of millions of years for it to take off.”
In his MIT researchFournier (featured below in the YouTube video) says that different age estimates can lead to conflicting evolutionary narratives. For instance, some analyses suggest oxygenic photosynthesis evolved very early on and progressed “like a slow fuse,” while others indicate it appeared much later and then “took off like wildfire” to trigger the Great Oxidation Event and the accumulation of oxygen in the biosphere. “In order for us to understand the history of habitability on Earth, it’s important for us to distinguish between these hypotheses,” he says.
An earlier version of this article was 2019 StudyThe theory is that the first explosion of oxygen was created by a series of volcanic eruptions caused by tectonics. James Eguchi, a NASA postdoctoral fellow at the University of California, Riverside said:”Most people think the rise of oxygen was linked to cyanobacteria, and they are not wrong. Photosynthetic organisms may release oxygen. However, the important question here is whether this emergence coincides or not with the timing. Great Oxidation Event. As it turns out, they do not.”
The First 1.5 billion years of life could have been lived on oxygen.
Plate Tectonics Not Necessary
“It looks like Earth’s history is calling for tectonics to play a big role in habitability, but that doesn’t necessarily mean that tectonics is absolutely necessary for oxygen build up,” said Rajdeep DasguptaThe principal investigator in a NASA-funded NASA-funded effort called CLEVER PlanetsThat is why he is currently exploring the possibility of life-essential elements combining on distant exoplanets. He explained that understanding the history of Earth’s habitability is essential for studying its evolution and how it became habitable. “There might be other ways of building and sustaining oxygen, and exploring those is one of the things we’re trying to do in CLEVER Planets.”
The study by geoscientists at Rice University offered a new theory to help explain the appearance of significant concentrations of oxygen in Earth’s atmosphere about 2.5 billion years ago, something scientists call the Great Oxidation Event (GOE). The research was published in Nature Geoscience.
“What makes this unique is that it’s not just trying to explain the rise of oxygen,” said Eguchi. “It’s also trying to explain some closely associated surface geochemistry, a change in the composition of carbon isotopes, that is observed in the carbonate rock record a relatively short time after the oxidation event. We’re trying to explain each of those with a single mechanism that involves the deep Earth interior, tectonics and enhanced degassing of carbon dioxide from volcanoes.”
Eguchi’s co-authors are Dasgupta, an experimental and theoretical geochemist and professor in Rice’s Department of Earth, Environmental and Planetary Sciences, and Johnny SealesRice graduate student, he helped to calculate the model that validated the theory.
500 million years earlier than the GOE, Cyanobacteria lived.
Scientists have long pointed to photosynthesis — a process that produces waste oxygen — as a likely source for increased oxygen during the GOE. Dasgupta said the new theory doesn’t discount the role that the first photosynthetic organisms, cyanobacteria, played in the GOE.
The GOE was 500 million years ago when Cyanobacteria lived on Earth. While a number of theories have been offered to explain why it might have taken that long for oxygen to show up in the atmosphere, Dasgupta said he’s not aware of any that have simultaneously tried to explain a marked change in the ratio of carbon isotopes in carbonate minerals that began about 100 million years after the GOE. This is known as the Geological Overlap. Lomagundi EventIt lasted for hundreds of millions of years.
One hundred carbon atoms is the isotope of carbon-13 and the remaining 99 are carbon-12. This ratio is well documented in carbonates formed before and after Lomagundi. However, those formed during this event contain about 10% more carbon-13.
Eguchi claimed that the GOE-related explosion in cyanobacteria has been long regarded as a contributing factor to Lomagundi.
Increase in the carbon-13-to-carbon-12 ratio occurs up to 10s of millions of years after oxygen rose
“Cyanobacteria prefer to take carbon-12 relative to carbon-13,” he said. “So when you start producing more organic carbon, or cyanobacteria, then the reservoir from which the carbonates are being produced is depleted in carbon-12.”
Eguchi claimed that people tried this to explain Lomagundi. But timing was again a problem.
“When you actually look at the geologic record, the increase in the carbon-13-to-carbon-12 ratio actually occurs up to 10s of millions of years after oxygen rose,” he said. “So then it becomes difficult to explain these two events through a change in the ratio of organic carbon to carbonate.”
To explain these factors, Eguchi Dasgupta, Seales came up with the following scenario:
–A dramatic increase in tectonic activity led to the formation of hundreds of volcanoes that spewed carbon dioxide into the atmosphere.
–The climate warmed, increasing rainfall, which in turn increased “weathering,” the chemical breakdown of rocky minerals on Earth’s barren continents.
–Weathering produced a mineral-rich runoff that poured into the oceans, supporting a boom in both cyanobacteria and carbonates.
–The organic and inorganic carbon from these wound up on the seafloor and was eventually recycled back into Earth’s mantle at subduction zones, where oceanic plates are dragged beneath continents.
–When sediments remelted into the mantle, inorganic carbon, hosted in carbonates, tended to be released early, re-entering the atmosphere through arc volcanoes directly above subduction zones.
–Organic carbon, which contained very little carbon-13, was drawn deep into the mantle and emerged hundreds of millions of years later as carbon dioxide from island hotspot volcanoes like Hawaii.
A new theory on the rise of oxygen that fueled evolution of life
A huge cyclic process
“It’s kind of a big cyclic process,” Eguchi said. “We do think the amount of cyanobacteria increased around 2.4 billion years ago. This would explain the oxygen increase. However, the increase in cyanobacteria can be offset by an increase in carbonates. So that carbon-12-to-carbon-13 ratio doesn’t change until both the carbonates and organic carbon, from cyanobacteria, get subducted deep into the Earth. Geochemistry kicks in, and these two forms become part of the mantle for different times. Magna are more effective at releasing carbonates and they can be released to the surface within a very short time. Lomagundi starts when the first carbon-13-enriched carbon from carbonates returns to the surface, and it ends when the carbon-12-enriched organic carbon returns much later, rebalancing the ratio.”
Eguchi stated that the study emphasizes how important deep Earth processes are in the evolution life on the surface.
“We’re proposing that carbon dioxide emissions were very important to this proliferation of life,” he said. “It’s really trying to tie in how these deeper processes have affected surface life on our planet in the past.”
This research was funded by NASA (80NSSC18K0828), the National Science Foundation (OCE-13338842), and Deep Carbon Observatory.
Avi ShporerResearch Scientist with the MIT Kavli Institute for Astrophysics and Space Research via MIT, NatureAnd Rice University
Image credit: Shutterstock LIcense
Avi Shporer Research Scientist, MIT Kavli Institute for Astrophysics and Space Research. A Google ScholarAvi was previously a NASA Sagan Fellow at the Jet Propulsion Laboratory (JPL). His motto, not surprisingly, is a quote from Carl Sagan: “Somewhere, something incredible is waiting to be known.”
