amount of wear and fragmentation of a fossil can allow scientists to estimate the amount of
wave action or the frequency of storms.
Often fossils of marine organisms are found on or near tall mountains. For example, the
Himalayas, the tallest mountains in the world, contain trilobites, brachiopods, and other
marine fossils. This indicates that rocks on the seabed have been uplifted to form huge
mountains. In the case of the Himalayas, this happened when the Indian Subcontinent
began to ram into Asia about 40 million years ago.
Fossils can also reveal clues about past climate. For example, fossils of plants and coal beds
have been found in Antarctica. Although Antarctica is frozen today, in the past it must have
been much warmer. This happened both because Earth’s climate has changed and because
Antarctica has not always been located at the South Pole.
One of the most fascinating patterns revealed by the fossil record is a number of mass
extinctions, times when many species died off. Although the mass extinction that killed
the dinosaurs is most famous, the largest mass extinction in Earth history occurred at the
end of the Permian period, about 250 million years ago. In this catastrophe, it is estimated
that over 95% of species on Earth went extinct! The cause of these mass extinctions is not
definitely known, but most scientists believe that collisions with comets or asteroids were
the cause of at least a few of these disasters.
Lesson Summary
- A fossil is any remains of ancient life. Fossils can be body fossils, which are remains
of the organism itself or trace fossils, such as burrows, tracks, or other evidence of
activity. - Preservation as a fossil is a relatively rare process. The chances of becoming a fossil
are enhanced by quick burial and the presence of preservable hard parts, such as bones
or shells. - Fossils form in five ways: preservation of original remains, permineralization, molds
and casts, replacement, and compression. - Rock formations with exceptional fossils are called very important for scientists to
study. They allow us to see information about organisms that we may not otherwise
ever know. - Index fossils are fossils that are widespread but only existed for a short period of time.
Index fossils help scientists to find the relative age of a rock layer and match it up with
other rock layers. - Living fossils are organisms that haven’t changed much in millions of years and are
still alive today. - Fossils give clues about the history of life on Earth, environments, climate, movement
of plates, and other events.