What geological evidence could there be for the presence of an early ocean? Select one:

a.
Marine sedimentary rocks can be dated back about 4 billion years.

b.
The iron contained in the rocks combined with the oxygen to form reddish iron oxides.

c.
Oxygen is needed to make ozone, a molecule made of three oxygen ions, O3.

d.
No animals would have been able to breathe in Earth's early atmosphere.