Rocks, like airplane flight recorders,
store in their interior very useful
information about what has
happened in the past. Whether forming
caves in the middle of mountains, mixed
among folds, or lying at the bottom of
lakes and oceans, stones are everywhere,
and they hold clues to the past. By
studying rocks, we can reconstruct the
history of the Earth. Even the most
insignificant rocks can tell stories about
other times, because rocks have been
around since the beginning of the universe.
They were part of the cloud of dust and
gases that revolved around the Sun over
four billion years ago. Rocks have been
silent witnesses to the cataclysms our
planet has experienced. They know the
cold of the glacial era, the intense heat of
the Earth's interior, and the fury of the
oceans. They store much information
about how external agents, such as wind,
rain, ice, and temperature changes, have
been altering the planet's surface for
millions of years.