[meteorite-list] Scientists Make Key Discovery About the Atmosphere of Early Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 2 Dec 2011 08:59:51 -0800 (PST)
Message-ID: <201112021659.pB2GxpaK013971_at_zagami.jpl.nasa.gov>

http://news.rpi.edu/update.do?artcenterkey=2953&setappvar=page%281%29

Setting the Stage for Life: Scientists Make Key Discovery About the
Atmosphere of Early Earth

Rensselaer Polytechnic Institute News Release
November 30, 2011

Scientists in the New York Center for Astrobiology at Rensselaer
Polytechnic Institute have used the oldest minerals on Earth to
reconstruct the atmospheric conditions present on Earth very soon after
its birth. The findings, which appear in the Dec. 1 edition of the
journal Nature, are the first direct evidence of what the ancient
atmosphere of the planet was like soon after its formation and directly
challenge years of research on the type of atmosphere out of which life
arose on the planet.

The scientists show that the atmosphere of Earth just 500 million years
after its creation was not a methane-filled wasteland as previously
proposed, but instead was much closer to the conditions of our current
atmosphere. The findings, in a paper titled "The oxidation state of
Hadean magmas and implications for early Earth's atmosphere," have
implications for our understanding of how and when life began on this
planet and could begin elsewhere in the universe. The research was
funded by NASA.

For decades, scientists believed that the atmosphere of early Earth was
highly reduced, meaning that oxygen was greatly limited. Such
oxygen-poor conditions would have resulted in an atmosphere filled with
noxious methane, carbon monoxide, hydrogen sulfide, and ammonia. To
date, there remain widely held theories and studies of how life on Earth
may have been built out of this deadly atmosphere cocktail.

Now, scientists at Rensselaer are turning these atmospheric assumptions
on their heads with findings that prove the conditions on early Earth
were simply not conducive to the formation of this type of atmosphere,
but rather to an atmosphere dominated by the more oxygen-rich compounds
found within our current atmosphere - including water, carbon dioxide,
and sulfur dioxide.

"We can now say with some certainty that many scientists studying the
origins of life on Earth simply picked the wrong atmosphere," said Bruce
Watson, Institute Professor of Science at Rensselaer.

The findings rest on the widely held theory that Earth's atmosphere was
formed by gases released from volcanic activity on its surface. Today,
as during the earliest days of the Earth, magma flowing from deep in the
Earth contains dissolved gases. When that magma nears the surface, those
gases are released into the surrounding air.

"Most scientists would argue that this outgassing from magma was the
main input to the atmosphere," Watson said. "To understand the nature of
the atmosphere 'in the beginning,' we needed to determine what gas
species were in the magmas supplying the atmosphere."

As magma approaches the Earth's surface, it either erupts or stalls in
the crust, where it interacts with surrounding rocks, cools, and
crystallizes into solid rock. These frozen magmas and the elements they
contain can be literal milestones in the history of Earth.

One important milestone is zircon. Unlike other materials that are
destroyed over time by erosion and subduction, certain zircons are
nearly as old as the Earth itself. As such, zircons can literally tell
the entire history of the planet - if you know the right questions to ask.

The scientists sought to determine the oxidation levels of the magmas
that formed these ancient zircons to quantify, for the first time ever,
how oxidized were the gases being released early in Earth???s history.
Understanding the level of oxidation could spell the difference between
nasty swamp gas and the mixture of water vapor and carbon dioxide we are
currently so accustomed to, according to study lead author Dustin Trail,
a postdoctoral researcher in the Center for Astrobiology.

"By determining the oxidation state of the magmas that created zircon,
we could then determine the types of gases that would eventually make
their way into the atmosphere," said Trail.

To do this Trail, Watson, and their colleague, postdoctoral researcher
Nicholas Tailby, recreated the formation of zircons in the laboratory at
different oxidation levels. They literally created lava in the lab. This
procedure led to the creation of an oxidation gauge that could then be
compared with the natural zircons.

During this process they looked for concentrations of a rare Earth metal
called cerium in the zircons. Cerium is an important oxidation gauge
because it can be found in two oxidation states, with one more oxidized
than the other. The higher the concentrations of the more oxidized type
cerium in zircon, the more oxidized the atmosphere likely was after
their formation.

The calibrations reveal an atmosphere with an oxidation state closer to
present-day conditions. The findings provide an important starting point
for future research on the origins of life on Earth.

"Our planet is the stage on which all of life has played out," Watson
said. "We can't even begin to talk about life on Earth until we know
what that stage is. And oxygen conditions were vitally important because
of how they affect the types of organic molecules that can be formed."

Despite being the atmosphere that life currently breathes, lives, and
thrives on, our current oxidized atmosphere is not currently understood
to be a great starting point for life. Methane and its oxygen-poor
counterparts have much more biologic potential to jump from inorganic
compounds to life-supporting amino acids and DNA. As such, Watson thinks
the discovery of his group may reinvigorate theories that perhaps those
building blocks for life were not created on Earth, but delivered from
elsewhere in the galaxy.

The results do not, however, run contrary to existing theories on life's
journey from anaerobic to aerobic organisms. The results quantify the
nature of gas molecules containing carbon, hydrogen, and sulfur in the
earliest atmosphere, but they shed no light on the much later rise of
free oxygen in the air. There was still a significant amount of time for
oxygen to build up in the atmosphere through biologic mechanisms,
according to Trail.


Contact: Gabrielle DeMarco
Phone: (518) 276-6542
E-mail: demarg at rpi.edu
Received on Fri 02 Dec 2011 11:59:51 AM PST