Birth place of life on the Hadean Earth and early evolution of life on a tightrope

Monday, 15 December 2014
Shigenori Maruyama, Tokyo Institute of Technology, Tokyo, Japan
The surface environment of the Hadean Earth is the key to the beginning of life. For the emergence of life, primordial Earth has to evolve with the following conditions. 1) Primordial Earth was formed without an atmosphere and ocean components where ultra-reductive materials such as Fe3P were formed. 2) At about 4.4Ga, atmosphere and ocean components were delivered to the Earth through heavy bombardment of asteroid bodies. 3) Direct reaction between komatiite and primordial atmosphere, associated with pseudo-plate tectonics, fixed atmospheric CO2 into the crust, which resulted in decreased density of atmospheric CO2; because of this, a primordial ocean appeared, and the Earth did not become a burning planet like Venus. 4) The primordial ocean was too toxic because of high salinity, ultra acidity, and high concentrations of heavy metal elements. 5) It was impossible to bear life in such a toxic ocean. However, the mass of the primordial ocean was small, e.g. only 3-5km depth, which enabled a landmass to appear on Hadean Earth. The surface environment was highly diversified with numerous lakes and river systems interacting with the landmass (i.e., primordial continent), providing varied and dynamic conditions (ultra-reductive to acidic environment) where prebiotic chemical evolution progressed. 6) On the other hand, plate tectonics started once the primordial ocean was formed. Due to the chemical reaction between the rocks and ocean, the toxic ocean gradually neutralized.

 Considering these tight conditions towards the emergence of life, the birth of life progressed on the tightrope of the Hadean Earth.