This course serves as a survey of the history of life on Earth. There are three main kinds of fossils. The most biologically informative are body fossils , remains of past organisms and representations of their remains.
Trace fossils are indications of past organism activity.
An example of a rock bearing trace fossils shows the sinuous path of worm-like organisms grazing the surface of the sediment. Many trace fossils were once thought to represent fossilized seaweed, but seaweed is very difficult material to preserve, and comparisons with activities of modern organisms have allowed us to understand these markings as results of animal activity. The discoloration associated with many trace fossils is derived from chemical interaction between an organism's mucus and the sediment. Because they provide more information than trace and chemical fossils, body fossils are of primary interest to us. Although fossils are numerous, the fossil record is far from being a complete record of past life.