Why the fossil record contains an incomplete record of the history of life on earth?

Answer 1

We have an incomplete fossil record because the earth is continually re-cycling its' crust.

The oldest oceanic crust is less than 200 million years old and as most fossils are found in sediments deposited at the bottom of seas and oceans, this means that only the small amounts pushed up onto the edge of continents, when oceanic crust is subducted, are preserved.

Fossilization is only a very rare occurrence so many species of animals and plants never get the chance to become fossils.

There are other reasons; when an earthquake pushes up a part of the crust it disturbs the cycle of deposition of sediment. A drop in sea level would also do something similar. This means that if organisms were previously buried, a change of deposition could mean whole sections of sediment being washed away, along with the potential fossils.

Answer 2

1: Only a very small proportion of organisms get buried quickly enough to prevent them decomposing

2: Not all organisms have hard parts

3; Sediments containing fossils are continually being eroded and removed along with their fossil content

4: metamorphism and deformation destroy fossils

5: many fossils are still buried in rocks not exposed at the surface

6: the sea floor in particular is being continuously recycled, so deep marine organisms are seldom preserved.

To become a fossil an organism needs to have hard parts, die and be buried in an anaerobic environment very quickly, and then be preserved through geological time, without being destroyed by tectonism or metamorphism, or removed by erosion. These are pretty rare circumstances, so organisms becoming fossilized are the exceptions rather than the rule.

Written By SallyC

Answer 3

2 reasons

1 - because they haven't all been found and named yet

2- some of us haven't died out yet.

Fossil record can never be complete.