Scientists Make Key Discovery
About the Atmosphere of Early Earth
11/30/2011 - Rensselaer Polytechnic Institute (RPI) - Troy, N.Y. –
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.
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
To date, there remain widely held theories and studies of
how life on Earth may have been built out of this deadly atmosphere
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
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,”
“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.
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.
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.
The New York Center for Astrobiology
Based within the School of Science at Rensselaer Polytechnic
Institute in Troy, N.Y., the New York Center for Astrobiology is
devoted to investigating the origins of life on Earth and the
conditions that lead to formation of habitable planets in our own
and other solar systems.
Supported by NASA, the $7 million center is
a member of NASA’s Astrobiology Institute (NAI), and is a
partnership between Rensselaer and the University at Albany,
Syracuse University, the University of Arizona, and the University
of North Dakota.
Researchers and students within the center seek to
understand the chemical, physical, and geological conditions of
early Earth that set the stage for life on our planet.
look beyond our home planet to investigate whether the processes
that prepared the Earth for life could be replicated elsewhere — on
Mars and other bodies in our solar system, for example, and on
planets orbiting other stars.