Volcanism and Snowball Earth
Monday, 11. May 2009, 10:20:16
I am not a great believer in the “snowball earth” hypothesis, but that does not withhold me from finding it an interesting hypothesis worth further investigation. In short the hypotheses claims that the Earth's surface was nearly or entirely frozen at some points in its past. The occurrence of Snowball (or Slushball) Earths remains controversial. For more information I can refer to the the Snowball Earth website, that examines the evidence and theory behind the snowball earth hypothesis.
I cannot help mentioning that the world's largest deposit of manganese was formed by the cascade of chemical reactions caused when the planet got so cold that even the equators were icy-a condition according to research at the California Institute of Technology.
A suspected "snowball Earth" episode occurred between 2400 and 2300 million years ago, when much of the planet is thought to have been covered with ice.
In my post on A Breath of Fresh Air I briefly mentioned the Great Oxidation Event, that is generally believed to have taken place some 2300 million years ago.
Apparently we had a different environment and climate back then. According to a new study available online from 21 April 2009 in Earth and Planetary Science Letters (for subscribers or people willing to purchase it for US $ 31.50) a shutdown of volcanic activity over a period of 250 million years might have caused both the covering of our Earth with glaciers and the rise in atmospheric oxygen. Very little volcanic material has been dated to between 2450 and 2200 million years ago. This has been known for some time, but might be explained by a gap in the geologic records. An analysis of thousands of zircon minerals collected from all seven continents indicates, however, that the volcanism gap most probably is real, meaning that there was a major slowdown in the Earth's volcanic activity during this period.
The calm period may have been contemporaneous with a pause in the motion of tectonic plates, which drives much of Earth's volcanic activity. At this early stage in Earth's history, the Earth's interior was hotter and less viscous, and so less able to drag the tectonic plates. With no new carbon dioxide being emitted from volcanoes, its concentration in the atmosphere would have declined, leading to global cooling. Prior to the volcanic shutdown, any oxygen produced by marine microorganisms was consumed in reactions with iron in the ocean. With no fresh volcanic material to replenish the iron, oxygen would have been free to build up in the atmosphere.
According to a paper published in the May 2009 issue of Geology it appears that the “snowball Earth” ice age may have been due to the rise of oxygen in Earth's atmosphere, which consumed atmospheric greenhouse gases and chilled the earth. Once oxygen made it into the atmosphere, the scientists suggest that it reacted with methane, a powerful greenhouse gas, to form carbon dioxide, which is 62 times less effective at warming the surface of the planet. With less warming potential, surface temperatures may have plummeted, resulting in globe-encompassing glaciers and sea ice.
It all seems to fit nicely together - well the carbon dioxide part may sound like a bit of a contradiction, but in both cases the overall message is less greenhouse gas effect (be it from methane or carbon dioxide) leading to global cooling.
Reference:
Evidence and implications for a widespread magmatic shutdown for 250 My on Earth
By Condie et al.
in Earth and Planetary Science Letters
Volume 282, Issues 1-4, 30 May 2009, Pages 294-298
doi:10.1016/j.epsl.2009.03.033
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4W441GK-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b83c92bc506de42072315ad4601c49db
• http://www.newscientist.com/article/mg20227073.800-volcanic-shutdown-may-have-led-to-snowball-earth.html?DCMP=OTC-rss&nsref=environment
• http://www.terradaily.com/reports/Rise_Of_Oxygen_Caused_Earth_Earliest_Ice_Age_999.html
• http://www.geologytimes.com/research/The_rise_of_oxygen_caused_Earths_earliest_ice_age.asp
I cannot help mentioning that the world's largest deposit of manganese was formed by the cascade of chemical reactions caused when the planet got so cold that even the equators were icy-a condition according to research at the California Institute of Technology.
A suspected "snowball Earth" episode occurred between 2400 and 2300 million years ago, when much of the planet is thought to have been covered with ice.
In my post on A Breath of Fresh Air I briefly mentioned the Great Oxidation Event, that is generally believed to have taken place some 2300 million years ago.
Apparently we had a different environment and climate back then. According to a new study available online from 21 April 2009 in Earth and Planetary Science Letters (for subscribers or people willing to purchase it for US $ 31.50) a shutdown of volcanic activity over a period of 250 million years might have caused both the covering of our Earth with glaciers and the rise in atmospheric oxygen. Very little volcanic material has been dated to between 2450 and 2200 million years ago. This has been known for some time, but might be explained by a gap in the geologic records. An analysis of thousands of zircon minerals collected from all seven continents indicates, however, that the volcanism gap most probably is real, meaning that there was a major slowdown in the Earth's volcanic activity during this period.
The calm period may have been contemporaneous with a pause in the motion of tectonic plates, which drives much of Earth's volcanic activity. At this early stage in Earth's history, the Earth's interior was hotter and less viscous, and so less able to drag the tectonic plates. With no new carbon dioxide being emitted from volcanoes, its concentration in the atmosphere would have declined, leading to global cooling. Prior to the volcanic shutdown, any oxygen produced by marine microorganisms was consumed in reactions with iron in the ocean. With no fresh volcanic material to replenish the iron, oxygen would have been free to build up in the atmosphere.
According to a paper published in the May 2009 issue of Geology it appears that the “snowball Earth” ice age may have been due to the rise of oxygen in Earth's atmosphere, which consumed atmospheric greenhouse gases and chilled the earth. Once oxygen made it into the atmosphere, the scientists suggest that it reacted with methane, a powerful greenhouse gas, to form carbon dioxide, which is 62 times less effective at warming the surface of the planet. With less warming potential, surface temperatures may have plummeted, resulting in globe-encompassing glaciers and sea ice.
It all seems to fit nicely together - well the carbon dioxide part may sound like a bit of a contradiction, but in both cases the overall message is less greenhouse gas effect (be it from methane or carbon dioxide) leading to global cooling.
Reference:
Evidence and implications for a widespread magmatic shutdown for 250 My on Earth
By Condie et al.
in Earth and Planetary Science Letters
Volume 282, Issues 1-4, 30 May 2009, Pages 294-298
doi:10.1016/j.epsl.2009.03.033
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4W441GK-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b83c92bc506de42072315ad4601c49db
• http://www.newscientist.com/article/mg20227073.800-volcanic-shutdown-may-have-led-to-snowball-earth.html?DCMP=OTC-rss&nsref=environment
• http://www.terradaily.com/reports/Rise_Of_Oxygen_Caused_Earth_Earliest_Ice_Age_999.html
• http://www.geologytimes.com/research/The_rise_of_oxygen_caused_Earths_earliest_ice_age.asp
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