Tuesday, October 19, 2010

We're not in Kansas anymore....

This weeks lecturer will be discussing early Earth - going back in time to the point at which the first whiff of oxygen appeared.

The Hadean Era was the first in Earth history, extending from the first formation of continental crust, which began some time around 4.4 billion years becoming persistent soon after, to approximately 3.5 billion years. The earliest terrestrial environments were harsh: Levels of atmospheric oxygen around 1% were too low to sustain an ozone layer, without which there would have been little protection from solar radiation. High levels of atmospheric carbon dioxide and methane would have created a strong greenhouse effect, with global temperatures estimated to have been between 30 and 50°C. Oceans formed early, between 4.4 and 3.9 billion years, from condensation of atmospheric water vapor. Estimates suggest that the earliest oceans were hot (between 80 and 100°C) and acidic.

University of Colorado researcher Stephen Mojzsis explains what Earth might have looked like back then:

"Before 4 billion years ago, the Earth would not be recognizable for the pale blue world that we are familiar with today. Indeed, although we now understand that there were significant landmasses already present by that time, the denser carbon dioxide-rich atmosphere would have given the sky a reddish-tinge. The oceans, with a much higher concentration of iron than our contemporary oceans, would look a dark greenish-blue and these oceans would have bathed hundreds of small continents akin to New Zealand or the Japan arc,"

This weeks reading is a paper published by Mojzsis about evidence for life on earth at 3.4 billion years ago. Mojzsis measured carbon isotopes in inclusions within apatite grains. The isotopes (δ13C) were light – meaning they were enriched in 12C relative to 13C. Organisms turning CO2 into organic matter favor the 12C atoms over the 13C atoms because metabolic processes involving the lighter isotope occur faster. So inorganic carbon (C not fixed by organisms) has a δ13C of ~-10‰, carbonaceous fossils have a δ13C of ~-20 to -35‰ and photosynthesizers, ~-50 to -60‰.


  1. As I was reading this I was left wondering how the earth escaped from this not so pleasant past. How was the amount of carbon dioxide in the atmosphere reduced so that life could further develop and the earth cool? Is it all in the CO2 traps we referenced in earlier lectures? What is the risk of this process reversing and the earth again overheating?

    Also, I was amused by the soundtrack on the video. It makes fossils sound so ominous and foreboding.

  2. It never ceases to amaze me just how inhospitable Earth can be, and still support (or give rise to) life. Heat, it smack it, smother it, flood it, or freeze it - life somehow persists.

  3. I thought this was the best lecture so far, in the sense that Mojzsis did a great job of explaining everything. Instead of using a bunch of technical jargon, he explained all the complex terms and things that I wouldn't have understood otherwise. It's amazing how much more I understood this week because he explained things. It seemed like he really wanted everyone to be able to understand his material. Overall, I enjoyed the lecture!

  4. I really liked this lecture. Comparatively easy to understand and the explanations on how life developed. "Accuracy" took on a whole new meaning.

    I still wonder how, though, touching the rock samples without gloves is acceptable. I would think there were some traces of bacteria on hands. Also considering the fact that the guy hand a seemingly gold ring on made me a little more skeptical,