the Rock Record?
Geologists and other earth
scientists often refer to the rock record. The rock record is nothing more than
the rocks that currently exist. The rock record does not show a tidy, orderly
progression of geologic events. Rock formations are eroded, buried, torn
apart, melted, squashed together, even turned upside down. The only parts
of the Earth history "recorded" are "leftovers" that
haven't yet been recycled. That is, when an area undergoes change due to
a geologic process, the original rocks are often changed or destroyed, making
the investigation of the events that created the rock quite difficult. Nevertheless,
every thing we know about the history of the Earth has been learned from
studying the rock formed by geologic processes.
Geologic time is measured
in billions of years. Most of Earth's history is very sketchily recorded,
and the rock record for most of Earth's history is composed of rocks that have
been changed physically and chemically many times since it was first laid down.
The appearance of fossils in the rock record has made geologic investigation easier,
because the organisms that the fossils came from give us markers in the rock record.
Fossils also tell us many things about the environment present when the organisms