The Astronomical Evidence. It is thought that such meteorites were numerous near the end of the accretion period and thus could have been a significant source of additional organic building blocks. This finding also indicated that organic molecules may be prevalent in interstellar space. The Geological Evidence. Geologic evidence for the origin of early life comes from the study of rocks and fossils.
Fossils are the remains of organisms that became trapped and preserved in ancient sedimentary rock.
Microfossils found in rocks dating back more than 3.5 billion years provide the only direct evidence of early life. Some rocks provide evidence not of the organism itself, but rather of the activities of the organism. This more recent period is called the Phanerozoic and the abundant fossil record attests to the great diversity of life forms following the earlier Precambrian period which lasted over the first 4 billion years of Earth's history. No fossils with hard shell-like appendages are found in Precambrian rock. Early Stromatolites Figure 5.