Place: 4274 Chamberlin (refreshments will be served)
Speaker: Clark Johnson, UW Department of Geoscience
Abstract: Finding evidence for the earliest life on Earth requires a bit different approach than say digging for dinosaur bones, because the evidence is much more cryptic. Microbial life dominated the biosphere for perhaps 4 billion years, yet the number of known localities of undisputed microfossils is quite small. What is a weird spot under the microscope and what represents true cellular remains? Fossilized microbial communities (stromatolites), which give us a hint about ancient ecosystems, are even more rare, and also subject to debate. Another approach, one we are taking at UW-Madison, is to look for the fingerprints of ancient microbial metabolisms that are left in the isotopic record of element that are cycled by life. These can be found in remnant carbon compounds, or in inorganic minerals that may be the product of microbial metabolism. In addition, such fingerprints inform us about past environmental conditions that permit, or do not permit, life (liquid water, etc.). We will take a broad tour of these issues, focusing on what we know, and do not know, from the formation of the Earth at 4.5 b.y. ago up to the first major rise in atmospheric oxygen about 2 b.y. ago.