User:Milton Beychok/Sandbox
Earth was formed 4.54 billion years ago (within an uncertainty of 1%) with a primordial gaseous atmosphere surrounding a very dense, molten core. About 4.40 billion year ago, as the Earth began to cool and form a crust, the primordial atmosphere was stripped away by a combination of heat from that molten crust, periods of intense solar activity, and the solar wind.
As the crust formed, volcanic activity became incessant. The outgassing from the volcanoes replaced the primordial atmosphere with what is referred to as the secondary atmosphere that most probably consisted of steam (water vapor), nitrogen, methane, ammonia, carbon monoxide, carbon dioxide, hydrogen sulfide, sulfur dioxide, and other gases &mdssh; a mixture much like that emitted from volcanoes today. There was very little free oxygen (if any) in that secondary atmosphere and it would have been poisonous for almost all modern life forms.
References
- G.B. Dalrymple (1991). The Age of the Earth. California: Stanford University Press. ISBN 0-8047-1569-6.
- G.B. Dalrymple (2001). <a href="http://sp.lyellcollection.org/content/190/1/205.abstract">"The age of the Earth in the twentieth century: a problem (mostly) solved"</a>. Geological Society, London, Special Publications Vol. 190. Issue(1), pp. 205–221.
- William L. Newman, (2007). <a href="http://pubs.usgs.gov/gip/geotime/age.html>"Age of the Earth"</a>. Publications Services, U.S. Geological Survey (USGS).