Privileged Planet: when land masses appeared (Introduction)

by David Turell , Saturday, May 26, 2018, 15:08 (2373 days ago) @ dhw

QUOTES: 'Based on his own previous modeling and other studies, Bindeman said, total landmass on the planet 2.4 billion years ago may have reached about two-thirds of what is observed today. However, the emergence of the new land happened abruptly, in parallel with large-scale changes in mantle dynamics.

"At 2.4 billion years ago, Bindeman said, the newly emerged land began to consume carbon dioxide from the atmosphere amid chemical weathering.

"The timing also coincides with the transition from the Archean Eon, when simple prokaryotic life forms, archaea and bacteria, thrived in water, to the Proterozoic Eon, when eukaryotes, such as algae, plants and fungi, emerged.

"Exposure of the new land to weathering, he said, may have set off a sink of greenhouse gases such carbon dioxide, disrupting the radiative balance of the Earth that generated a series of glacial episodes between 2.4 billion and 2.2 billion years ago. That, he said, may have spawned the Great Oxygenation Event in which atmospheric changes brought significant amounts of free oxygen into the air.

dhw: I’ve cherry-picked these quotes, as I’m interested in the suddenness of environmental change coinciding with the emergence of new life forms. It seems to me that this offers a vital clue as to how evolution has progressed: once the mechanism for life, reproduction and change was in place (we needn’t concern ourselves here with the origin of the mechanism), organisms would have responded to those changes in one of three ways: extinction, adaptation, innovation. This could have taken place on a local as well as a global level.

It took a while for land organisms to appear. Fossils we find on land now were originally under water.