July 10, 2013
Early Earth Relied On Carbon To Keep Warm Enough For Life
Lee Rannals for redOrbit.com - Your Universe Online
University of Colorado Boulder researchers have figured out how early Earth was warm enough to support life when the sun was 20 per cent dimmer than today.
A new study determined that all that may have been required to sustain liquid water and primitive life on Earth during the Archean eon, 2.8 billion years ago, were the reasonable atmospheric carbon dioxide amounts believed to be present at the time and a little bit of methane.
The researchers wrote in the journal Astrobiology that, for the study, they used three-dimensional climate models which were run for thousands of hours on CU's Janus supercomputer.
"It's really not that hard in a three-dimensional climate model to get average surface temperatures during the Archean that are in fact moderate," said Eric Wolf, a doctoral student in CU-Boulder's atmospheric and oceanic sciences department. "Our models indicate the Archean climate may have been similar to our present climate, perhaps a little cooler. Even if Earth was sliding in and out of glacial periods back then, there still would have been a large amount of liquid water in equatorial regions, just like today."
Evolutionary biologists believe life began on Earth as simple cells about 3.5 billion years ago, which is about a billion years after the planet is thought to have formed. Scientists believe the first life may have evolved in shallow tide pools, freshwater ponds, freshwater or deep-sea hydrothermal vents. Some even hypothesize that life arrived on objects from space, such as comets.
Past studies have attempted to solve the paradox of how life could be sustained on a young Earth simply using one-dimensional models.
"In our opinion, the one-dimensional models of early Earth created by scientists to solve this paradox are too simple -- they are essentially taking the early Earth and reducing it to a single column atmospheric profile," said CU-Boulder Professor Brian Toon. "One-dimensional models are simply too crude to give an accurate picture."
The team used a general circulation model known as the Community Atmospheric Model version 3.0, which was developed by the National Center for Atmospheric Research in Boulder. This model contains three dimensional atmosphere, ocean, land, cloud and sea ice components. The researchers also tuned the model with a sophisticated radiative transfer component that allowed for the absorption, emission and scattering of solar energy and an accurate calculation of the greenhouse gas effect for the unusual atmosphere of early Earth.
"The leap from one-dimensional to three-dimensional models is an important step," said Wolf. "Clouds and sea ice are critical factors in determining climate, but the one-dimensional models completely ignore them."
Wolf said that the simplest solution of the paradox involves maintaining about 20,000 parts per million (ppm) of carbon dioxide and 1,000 ppm of methane in the ancient atmosphere. Today's current climate consists of 400 ppm CO2 in the atmosphere, but scientists have discovered ancient soil samples that show CO2 was much higher during that time. Methane is also about 20 times more powerful as a greenhouse gas than CO2, which could have played a significant role in warming the Earth.
"I don't want to be presumptuous here," said Wolf. "But we show that the paradox is definitely not as challenging as was believed over the past 40 years. While we can't say definitively what the atmosphere looked like back then without more geological evidence, it is certainly not a stretch at all with our model to get a warm early Earth that would have been hospitable to life."