Fossils - Record in the Rock

Earth History

Evolution – Record in the Rock

Fossils are the preserved remains or traces of living things.  They are formed when living things die and are buried by sediments.

Paleontologists are scientists who study, collect and classify fossils.

A mold is the hollow area in the sediment which shows the shape of an organism or a part of an organism.

A cast is the solid copy of the shape of an organism…usually formed when sediment fills in a mold or empty container (like a shell).

Petrified fossils are when minerals replace all or part of an organism…petrified wood.

Carbon film is an extremely thin coating of carbon on a rock showing the details of a previously live organisms.

Trace fossils provide evidence of the activities of ancient organisms –may include shards of pottery, arrow heads, imprints of a leaf or foot track.

Tar, ice or amber may actually preserve the remains of organisms with little or no change. 

The fossil record is the result of information gathered by paleontologists and may provide evidence of:

  • History of life on Earth
  • Groups of organisms changing over long periods of time
  • Earth’s past climate
  • Past environments and changes in Earth’s surface.

The fossil record provides evidence to support the theory of evolution.

  • Evolution – the gradual change in living things over long periods of time
  • Scientific theory – well-tested concept that explains a wide range of observations
  • Extinct – when an organism no long exists and never will again

We determine the age of a fossil by finding the age of the rock is was found in.

  • Relative age of a rock is when we compare the age of one rock to the age of another rock using things like index fossils.
  • Absolute age of a rock is determined by radioactive dating of materials found in the rock.  Carbon-14 is most commonly used for modern fossils.
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