Volcanic eruptions may have spurred first `whiffs' of oxygen in Earth's atmosphere

Date:
August 26, 2021
Source:
University of Washington
Summary:
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.



FULL STORY ==========================================================================
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
study led by the University of Washington, 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 Jana Meixnerova',
a UW 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 Ariel Anbar at Arizona State University analyzed
rocks from the Mount McRae Shale in Western Australia, reporting a
short-term whiff 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 Joel Blum, 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 Roger Buick, a UW 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," Meixnerova' 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," Meixnerova' 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 Eva Stu"eken,
a former UW astrobiology graduate student now at the University of
St. Andrews in Scotland; Michael Kipp, a former UW graduate student now
at the California Institute of Technology; and Marcus Johnson at the
University of Michigan. The study was funded by NASA, the NASA-funded
UW Virtual Planetary Laboratory team and the MacArthur Professorship to
Blum at the University of Michigan.

========================================================================== Story Source: Materials provided by University_of_Washington. Original
written by Hannah Hickey. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Jana Meixnerova', Joel D. Blum, Marcus W. Johnson, Eva E. Stu"eken,
Michael A. Kipp, Ariel D. Anbar, Roger Buick. Mercury abundance and
isotopic composition indicate subaerial volcanism prior to the end-
Archean "whiff" of oxygen. Proceedings of the National Academy of
Sciences, 2021; 118 (33): e2107511118 DOI: 10.1073/pnas.2107511118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210826111724.htm

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