Nav: Home

Sulfur dioxide may have helped maintain a warm early Mars

December 20, 2007

CAMBRIDGE, Mass. -- Sulfur dioxide (SO2) may have played a key role in the climate and geochemistry of early Mars, geoscientists at Harvard University and the Massachusetts Institute of Technology suggest in the Dec. 21 issue of the journal Science. Their hypothesis may resolve longstanding questions about evidence that the climate of the Red Planet was once much warmer than it is today.

The Science paper's authors are Itay Halevy, a Ph.D. candidate in Harvard's Department of Earth and Planetary Sciences; Daniel Schrag, professor of earth and planetary sciences and environmental engineering at Harvard; and Maria Zuber, professor of earth, atmospheric, and planetary sciences at MIT.

"There is abundant evidence for a warmer climate, perhaps even a liquid water ocean, early in Martian history, between 3.5 and 4 billion years ago," says Schrag, the paper's senior author. "However, scientists have found it difficult to reconcile this evidence with our understanding of how the climate system is regulated on Earth."

Over millions of years, the Earth's climate has been controlled by the carbon cycle and its effect on carbon dioxide, the main greenhouse gas. On Earth, there is a balance between carbon dioxide vented from volcanoes and chemical reactions with silicate rocks on the Earth's surface that remove carbon dioxide from the atmosphere and convert it to calcium carbonate, commonly known as limestone. Scientists believe that this balance has helped maintain Earth's habitability over the last 4 billion years.

On Mars, there is not enough volcanic activity today to maintain this cycle. But this was not true some 4 billion years ago, when a giant volcanic complex called Tharsis erupted over tens to hundreds of millions of years -- and also a time when evidence suggests Mars had a much warmer climate. However, this carbon cycle on early Mars should have produced vast quantities of limestone like on Earth, and yet almost none has been found.

The new hypothesis points the finger at sulfur dioxide, another gas released by volcanoes. Sulfur dioxide is a powerful greenhouse gas, like carbon dioxide, and it is more reactive with silicate rocks than carbon dioxide. On Earth, sulfur dioxide is rapidly oxidized to sulfate, and then removed from the atmosphere. The authors argue that the atmosphere of early Mars would have lacked oxygen, so sulfur dioxide would remain much, much longer.

"The sulfur dioxide would essentially preempt the role of carbon dioxide in surface weathering reactions," says Halevy, the first author of the report. "The presence of even a small amount of sulfur dioxide in the atmosphere would contribute to the warmer climate, and also prevent limestone deposits from forming."

In place of limestone, the authors predict that sulfur minerals would form in any standing water on Mars. This may explain the surprising finding of the rovers that have identified sulfur minerals as an abundant component of Martian soils.

"We think we now understand why there is so little carbonate on Mars, and so much sulfur," Halevy says.

"Our hypothesis may also be important for understanding the early Earth," Schrag says. "Before the origin of life, our atmosphere may have looked much like early Mars. Sulfur dioxide may have had an important role then as well."

If correct, the hypothesis implies that the oceans in which life evolved were much more acidic than previously thought. The early Earth may also provide a test for the hypothesis through the analysis of isotopes of sulfur in ancient mineral deposits.
-end-
Halevy, Schrag, and Zuber's work was funded by the NASA Planetary Geology and Geophysics program, the George Merck Fund of the New York Community Trust, and by a Radcliffe Fellowship to Zuber and a Harvard Origins of Life Initiative Graduate Fellowship to Halevy.

Harvard University

Related Mars Articles:

Getting mac and cheese to Mars
Washington State University scientists have developed a way to triple the shelf life of ready-to-eat macaroni and cheese, a development that could have benefits for everything from space travel to military use.
A material way to make Mars habitable
New research suggest that regions of the Martian surface could be made habitable with a material -- silica aerogel -- that mimics Earth's atmospheric greenhouse effect.
Life on Mars?
Researchers from Hungary have discovered embedded organic material in a Martian meteorite found in the late 1970s.
New evidence of deep groundwater on Mars
Researchers at the USC Arid Climate and Water Research Center (AWARE) have published a study that suggests deep groundwater could still be active on Mars and could originate surface streams in some near-equatorial areas on Mars.
Why we won't get to Mars without teamwork
If humanity hopes to make it to Mars anytime soon, we need to understand not just technology, but the psychological dynamic of a small group of astronauts trapped in a confined space for months with no escape, according to a paper published in American Psychologist, the flagship journal of the American Psychological Association.
More Mars News and Mars Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...