Who proposed the Big Bang Theory?

Match the following columns:

Column-$I$	Column-$II$
$P$. Origin of Earth	$I$. $4500 \, mya$
$Q$. Origin of Life	$II$. $4000 \, mya$
$R$. Origin of first cellular life	$III$. $3000 \, mya$
$S$. Origin of first non-cellular life	$IV$. $2000 \, mya$

The universe is approximately ........... years old.

The theory of abiogenesis or spontaneous generation was finally disapproved by

How was free ${O_2}$ released into the Earth's atmosphere,given that there was no free ${O_2}$ at the time of the origin of life?

$H.C. Urey$ wrote the following book: