fossils

Fossils are the remains.fossils are imprints and traces of once living
organisms preserved in the earth’s crust. They may be bones and teeth, shells, leaf
impressions, footprints, or burrows. The fossil record is our only evidence of more than 3.5
billion years that life has existed on earth. Fossils show us that:
• the first organisms on the planet were similar to living nonporous bacteria,
• there was a great diversification of multicellular animals in the oceans about 540 million
years ago,
• the first plants lived on land about 400 million years ago,
• four-legged creatures first walked on land about 350 million years ago,
• dinosaurs evolved about 220 million years ago, and
• mammals and modern birds became very diverse about 65 million years ago.
Fossils show how the physical earth has changed over time. By studying them we can investigate
the effects of climatic change over long periods of time. Fossils show us that:
• the climate has warmed and cooled,
• the positions of continents have changed, and
• mountains have been lifted up from ocean bottoms or continental lowlands.
Fossils also document the way living things respond to changing conditions. Without them, we
cannot understand the history of life on earth. The fossil record lets paleontologists test their
ideas about how the world works. Fossils reveal and help us understand:
• mass extinction of species at several times in the history of the planet,
• periods when many new forms appeared in a short time,
• genealogical relationships of living species to one another,
• rapid environmental changes in the past,
• effects of human-caused changes to the earth’s environment, and
• effects of environmental changes on biological diversity and ecological structure.