You had to be a good swimmer on Earth 2.5 billion years ago

William Atkins
Wednesday, 21 January 2009 22:30

Science - Biology

The Archean, or Archean, period is a geologic eon that occurred before the Proterozoic and Paleoproterozoic. It occurred before about 2.5 billion years ago.

They add, “During the Archaean a greater radiogenic crustal heat production and a greater mantle heat flow would have reduced the strength of the continental lithosphere, thus limiting crustal thickening due to mountain building processes and the maximum elevation in the Earth's topography …. Taking this into account, we show that the continents were mostly flooded until the end of the Archaean and that only 2–3% of the Earth's area consisted of emerged continental crust by around 2.5 Ga.”

Thus, as the mantle cooled, the crust became less thick, which lowered the height of the oceans and raised the land above the waters.

Also within their abstract, they state, “These results are consistent with widespread Archaean submarine continental flood basalts, and with the appearance and strengthening of the geochemical fingerprint of felsic sources in the sedimentary record from [about] 2.5 Ga."

And, "The progressive emergence of the continents as shown by our models from the late-Archaean onward had major implications for the Earth's environment, particularly by contributing to the rise of atmospheric oxygen and to the geochemical coupling between the Earth's deep and surface reservoirs.”

The New Scientist article “When Earth really as the blue planet” states, “The team believe[s] that this transition may help to explain why levels of oxygen in the atmosphere rose around this time. During the water-world period, any oxygen produced by photosynthesizing bacteria would have been quickly used up through reactions with decaying organic matter in the oceans.”

Further, “When the newly emerged land eroded, it produced sediment that; once washed into the oceans, would have buried the organic matter, preventing any further reactions with oxygen, and so allowing it to build up in the atmosphere.” [January 3-9, 2009, page 8]

Thus, oxygen built up in the atmosphere, which allowed organisms that breathed in oxygen to flourish. Due in part to this period of Earth’s early history, we are now a living, breathing species, like the other simple and complex multitudes of creatures living on, above, and underneath the surface of planet Earth.