The Origins of Life

CNRS international magazine, no 25
April 2012

The Search for Evidence

p 22

Earth's History, in billions (Ga) and millions (Ma) of years

Hadean -4,57 Ga Collapse of an interstellar cloud in the center of which the Sun formed in a mere 100 , 000 years.
-4,56 Ga Formation of the planets of the Solar System. The Earth came into existence in just a few tens of millions of years.
-4,5 Ga The Earth acquired an internal structure: in the center, an iron core, surrounded by a silicate mantle. The magnetic field generated by the motion of the metallic core appeared for the first time. The surface of the planet was a magma ocean.
-4,4 Ga Water, initially in a gaseous state, condensed to form the oceans.
-4,2 Ga The oldest known rocks, discovered in Canada.
Archean -3,9 Ga-4,2 Ga The last heavy meteorite bombardment.
-3,8 Ga Controversial traces of biological activity in rocks in Greenland.
-3,5 Ga Oldest traces of suspected biological activity.
-2,7 Ga Oldest confirmed stromatolites.
Proterozoic -2,4 Ga Increasing levels of oxygen in the atmosphere caused by the oxygenic photosynthetic activity of cyanobacteria.
-2 Ga Possibly the first eukaryotic cells.
Cambrian -540 Ma The Cambrian explosion: the rise of macroscopic diversity.

The Three Pillars of Life

p. 24
"Life is a system whose properties give it stability far from thermodynamical equilibrium" (Robert Pascal, physical chemist)

CNRS international magazine
Marc Girod