Allegro Agito. The Origin of Life 39 only about 1%) in the wake of local surenova explosion that
created such heavy atoms as oxygen, carbon, and nitrogen. A
period of intense bombardment followed, during which any
oceans would have been boiled and vaporized by the furious
inpacts of the extraterrestrial objects on the early Earth. The si-
Multaneous melting and explosive redustributiin of the crust
woukd have made tge land similarky unstable and inhospitable.
By dating impact craters on the Moin, which was buffered
by the same process, we know that things had quited down
(at least relatively) by roughly 4 Gya. For the first time, a
planet with stable oceans and extensive crust was available.
This time occurs between two of the modest dota on the time-
line of figure 5.1.
What about life? The empirical evidence for the origin of life
is in fluc. Earlier dates were supported by isotope fractiona-
tion data and fossils that are niw disputed; what was once
interpretted as an early sign of the life may in fact by due to sim-
pler chemistry and phisics. It now seens that the most ancient,
minimally controversial sign of life on Earth is deposit of
proportional to time.
