What the rise of oxygen on early Earth tells us about life on other
planets
Deeper understanding of Earth's atmosphere could help us identify signs
of life beyond our solar system

Date:
January 31, 2022
Source:
McGill University
Summary:
When did the Earth reach oxygen levels sufficient to support animal
life? Researchers have discovered that a rise in oxygen levels
occurred in step with the evolution and expansion of complex,
eukaryotic ecosystems. Their findings represent the strongest
evidence to date that extremely low oxygen levels exerted an
important limitation on evolution for billions of years.



FULL STORY ==========================================================================
When did the Earth reach oxygen levels sufficient to support animal life? Researchers from McGill University have discovered that a rise in oxygen
levels occurred in step with the evolution and expansion of complex,
eukaryotic ecosystems. Their findings represent the strongest evidence
to date that extremely low oxygen levels exerted an important limitation
on evolution for billions of years.


========================================================================== "Until now, there was a critical gap in our understanding of environmental drivers in early evolution. The early Earth was marked by low levels
of oxygen, till surface oxygen levels rose to be sufficient for animal
life. But projections for when this rise occurred varied by over a billion years - - possibly even well before animals had evolved," says Maxwell
Lechte, a postdoctoral researcher in the Department of Earth and Planetary Sciences under the supervision of Galen Halverson at McGill University.

Ironstones provide insights into early life To find answers, the
researchers examined iron-rich sedimentary rocks from around the world deposited in ancient coastal environments. In analyzing the chemistry
of the iron in these rocks, the researchers were able to estimate the
amount of oxygen present when the rocks formed, and the impact it would
have had on early life like eukaryotic microorganisms -- the precursors
to modern animals.

"These ironstones offer insights into the oxygen levels of shallow marine environments, where life was evolving. The ancient ironstone record
indicates around less than 1 % of modern oxygen levels, which would have
had an immense impact on ecological complexity," says Changle Wang,
a researcher at the Chinese Academy of Sciences who co-led the study
with Lechte.

"These low oxygen conditions persisted until about 800 million years
ago, right when we first start to see evidence of the rise of complex ecosystems in the rock record. So if complex eukaryotes were around
before then, their habitats would have been restricted by low oxygen,"
says Lechte.

Earth remains the only place in the universe known to harbor life. Today, Earth's atmosphere and oceans are rich with oxygen, but this wasn't always
the case. The oxygenation of the Earth's ocean and atmosphere was the
result of photosynthesis, a process used by plants and other organisms
to convert light into energy -- releasing oxygen into the atmosphere
and creating the necessary conditions for respiration and animal life.

Searching for signs of life beyond our solar system According to the researchers, the new findings suggests that Earth's atmosphere was
capable of maintaining low levels of atmospheric oxygen for billions
of years. This has important implications for exploration of signs of
life beyond our solar system, because searching for traces of atmospheric oxygen is one way to look for evidence of past or present life on another planet -- or what scientists call a biosignature.

Scientists use Earth's history to gauge the oxygen levels under which terrestrial planets can stabilize. If terrestrial planets can stabilize
at low atmospheric oxygen levels, as suggested by the findings, the
best chance for oxygen detection will be searching for its photochemical byproduct ozone, say the researchers.

"Ozone strongly absorbs ultraviolet light, making ozone detection possible
even at low atmospheric oxygen levels. This work stresses that ultraviolet detection in space-based telescopes will significantly increase our
chances of finding likely signs of life on planets outside our solar
system," says Noah Planavsky, a biogeochemist at Yale University.

More geochemical studies of rocks from this time period will allow
scientists to paint a clearer picture of the evolution of oxygen levels
during this time, and better understand the feedbacks on the global
oxygen cycle, say the researchers.

========================================================================== Story Source: Materials provided by McGill_University. Note: Content
may be edited for style and length.


========================================================================== Related Multimedia:
* Ironstone_deposits_along_a_rocky_ridge ========================================================================== Journal Reference:
1. Changle Wang, Maxwell A. Lechte, Christopher T. Reinhard, Dan Asael,
Devon B. Cole, Galen P. Halverson, Susannah M. Porter, Nir Galili,
Itay Halevy, Robert H. Rainbird, Timothy W. Lyons, and Noah
J. Planavsky.

Strong evidence for a weakly oxygenated ocean-atmosphere system
during the Proterozoic. PNAS, 2022 DOI: 10.1073/pnas.2116101119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220131161546.htm

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