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What Is a Fossil?

Fossils are evidence of ancient life preserved within sedimentary rocks. They are clues to what living things, ecosystems, and environments were like since life has existed on this planet. The oldest fossils are mats of blue-green algae that lived as much as 3.5 billion years ago. The youngest fossils are animals that lived approximately 10,000 years ago, before the beginning of recorded history.

Scientists that study fossils know that the types of creatures have changed dramatically over the millions and millions of years of Earth history. Most fossils are from animals, plants and other organisms that no longer live on the planet because, like dinosaurs, they have become extinct. In fact, about 99% of fossils are from extinct organisms. Many of these extinct species, or types of life forms, are similar to species that live today.

It is not just scientists that are able to find fossils! In some areas of the world, the rock exposed at the surface is made almost entirely of fossils making them easy to find. In other places, the rocks at the surface are not the type of sedimentary rocks where fossils are typically preserved. However, you can still find fossils in your local science or natural history museum. Even if you are from a place where fossils are difficult to find, you probably rely on fossils everyday by using fossil fuels such as oil, gas, or coal to power cars, lights, and heat or cool your house. Fossil fuels are organic carbon from plants and marine life that lived millions of years ago.

Body fossils are the preserved remains of actual organisms. Most living things never become fossils because it takes special conditions for a fossil to form. Parts made of mineral such as shells and bones are much more likely to become body fossils than soft tissues, such as skin, organs, and eyes, which usually decay. Animals like jellyfish, which have no bones, are rarely preserved.

Trace fossils are indirect evidence of ancient life. For instance, if you were to make footprints on the beach today and the beach sand eventually became cemented together forming a rock called sandstone, your footprints, if left undisturbed, would be in the rock and would be called trace fossils. This doesn�t happen very often. Think about all the people, dogs, crabs, birds and other animals that walk over a beach each day. Few, if any, of those footprints will become fossils someday. Most of them are washed away by wind and waves. Other examples of trace fossils include crab burrows, dinosaur bite marks, and bear claw starches on the walls of caves.

Last modified June 11, 2009 by Jennifer Bergman.

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The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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