Featured Research

from universities, journals, and other organizations

Model Gives Clearer Idea Of How Oxygen Came To Dominate Earth's Atmosphere

Date:
August 12, 2005
Source:
University of Washington
Summary:
A new model offers plausible scenarios for how oxygen came to dominate Earth's atmosphere 2.4 billion years ago, and why it took at least 300 million years after bacterial photosynthesis started producing oxygen in large quantities.

A number of hypotheses have been used to explain how free oxygenfirst accumulated in Earth's atmosphere some 2.4 billion years ago, buta full understanding has proven elusive. Now a new model offersplausible scenarios for how oxygen came to dominate the atmosphere, andwhy it took at least 300 million years after bacterial photosynthesisstarted producing oxygen in large quantities.

Related Articles


The big reason for the long delay was that processes such asvolcanic gas production acted as sinks to consume free oxygen before itreached levels high enough to take over the atmosphere, said MarkClaire, a University of Washington doctoral student in astronomy andastrobiology. Free oxygen would combine with gases in a volcanic plumeto form new compounds, and that process proved to be a significantoxygen sink, he said.

Another sink was iron delivered to the Earth's outer crust bybombardment from space. Free oxygen was consumed as it oxidized, orrusted, the metal.

But Claire said that just changing the model to reflectdifferent iron content in the outer crust makes a huge difference inwhen the model shows free oxygen filling the atmosphere. Increasing theactual iron content fivefold would have delayed oxygenation by morethan 1 billion years, while cutting iron to one-fifth the actual levelwould have allowed oxygenation to happen more than 1 billion yearsearlier.

"We were fairly surprised that we could push the transition abillion years in either direction, because those levels of iron in theouter crust are certainly plausible given the chaotic nature of howEarth formed," he said.

Claire and colleagues David Catling, a UW affiliate professorin atmospheric sciences, and Kevin Zahnle of the National Aeronauticsand Space Administration's Ames Research Center in California willdiscuss their model tomorrow (Aug. 9) in Calgary, Alberta, during theGeological Society of America's Earth System Processes 2 meeting.

Earth's oxygen supply originated with cyanobacteria, tinywater-dwelling organisms that survive by photosynthesis. In thatprocess, the bacteria convert carbon dioxide and water into organiccarbon and free oxygen. But Claire noted that on the early Earth, freeoxygen would quickly combine with an abundant element, hydrogen orcarbon for instance, to form other compounds, and so free oxygen didnot build up in the atmosphere very readily. Methane, a combination ofcarbon and hydrogen, became a dominant atmospheric gas.

With a sun much fainter and cooler than today, methane buildupwarmed the planet to the point that life could survive. But methane wasso abundant that it filled the upper reaches of the atmosphere, wheresuch compounds are very rare today. There, ultraviolet exposure causedthe methane to decompose and its freed hydrogen escaped into space,Claire said.

The loss of hydrogen atoms to space allowed increasinglygreater amounts of free oxygen to oxidize the crust. Over time, thatslowly diminished the amount of hydrogen released from the crust by thecombination of pressure and temperature that formed the rocks in thecrust.

"About 2.4 billion years ago, the long-term geologic sourcesof oxygen outweighed the sinks in a somewhat permanent fashion," Clairesaid. "Escaping to space is the only permanent escape that we envisionfor the hydrogen, and that drove the planet to a higher oxygen level."

The model developed by Claire, Catling and Zahnle indicatesthat as hydrogen atoms stripped from methane escaped into space,greenhouse conditions caused by the methane blanket quickly collapsed.Earth's average temperature likely cooled by about 30 degrees Celsius,or 54 degrees Fahrenheit, and oxygen was able to dominate theatmosphere because there was no longer an overabundance of hydrogen toconsume the oxygen.

The work is funded by NASA's Astrobiology Institute and theNational Science Foundation's Integrative Graduate Education andResearch Traineeship program, both of which foster research tounderstand life in the universe by examining the limits of life onEarth.

"There is interest in this work not just to know how an oxygenatmosphere came about on Earth but to look for oxygen signatures forother Earth-like planets," Claire said.


Story Source:

The above story is based on materials provided by University of Washington. Note: Materials may be edited for content and length.


Cite This Page:

University of Washington. "Model Gives Clearer Idea Of How Oxygen Came To Dominate Earth's Atmosphere." ScienceDaily. ScienceDaily, 12 August 2005. <www.sciencedaily.com/releases/2005/08/050811104910.htm>.
University of Washington. (2005, August 12). Model Gives Clearer Idea Of How Oxygen Came To Dominate Earth's Atmosphere. ScienceDaily. Retrieved October 25, 2014 from www.sciencedaily.com/releases/2005/08/050811104910.htm
University of Washington. "Model Gives Clearer Idea Of How Oxygen Came To Dominate Earth's Atmosphere." ScienceDaily. www.sciencedaily.com/releases/2005/08/050811104910.htm (accessed October 25, 2014).

Share This



More Earth & Climate News

Saturday, October 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

EU Gets Climate Deal, UK PM Gets Knock

EU Gets Climate Deal, UK PM Gets Knock

Reuters - Business Video Online (Oct. 24, 2014) EU leaders achieve a show of unity by striking a compromise deal on carbon emissions. But David Cameron's bid to push back EU budget contributions gets a slap in the face as the European Commission demands an extra 2bn euros. David Pollard reports. Video provided by Reuters
Powered by NewsLook.com
Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Deep Sea 'mushroom' Could Be Early Branch on Tree of Life

Reuters - Innovations Video Online (Oct. 24, 2014) Miniature deep sea animals discovered off the Australian coast almost three decades ago are puzzling scientists, who say the organisms have proved impossible to categorise. Academics at the Natural History of Denmark have appealed to the world scientific community for help, saying that further information on Dendrogramma enigmatica and Dendrogramma discoides could answer key evolutionary questions. Jim Drury has more. Video provided by Reuters
Powered by NewsLook.com
Raw: Tornado Rips Roofs in Washington State

Raw: Tornado Rips Roofs in Washington State

AP (Oct. 24, 2014) A rare tornado ripped roofs off buildings, uprooted trees and shattered windows Thursday afternoon in the southwest Washington city of Longview, but there were no reports of injuries. (Oct. 24) Video provided by AP
Powered by NewsLook.com
Fast-Moving Lava Headed For Town On Hawaii's Big Island

Fast-Moving Lava Headed For Town On Hawaii's Big Island

Newsy (Oct. 24, 2014) Lava from the Kilauea volcano on Hawaii's Big Island has accelerated as it travels toward a town called Pahoa. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins