Biology: Evolution Report

Fossils/Fossil record-

Fossils are evidence of organisms that lived in the past. They may be direct (i.e. bones, teeth, shells, pollen) or indirect (i.e. footprints, teeth marks, nests).

Through fossils we are able to discover the ancestry of present animals from extinct animals, we are also able to determine the time of a significant environmental change (e.g. ice age)

Fossils become trapped in sedimentary or volcanic rock, which produce layers of different fossils, showing different species from different time periods in each. Primitive fossils are found in older sediment. A new fossil type/rock layer marks a change in environment, creating new niches and selection pressures thus new species.

Fossil Record- The collection of fossils of all sorts that provides a record of extinct life.

Relative/Actual Dating-

Relative- Refers to a general time period, e.g. 0.5 - 1 million years ago.

These methods do not employ the use of isotopes to date fossils.

* Thermoluminescence- Measures the light emitted by a sample of quartz/zircon grains that has been exposed to sunlight or fire in the distant past. Useful with ceramics, quartz and carbonates 200,000-1000 years old.

* Palaeomagnetism- Shows the alignment of the Earth's magnetic field at the time when the rock sample was last heated above a critical level. Useful for rocks containing iron-bearing minerals 100 million-5000 years old.

Actual (absolute) - Refers to a particular, specific time period, e.g. 1000 years ago. It puts a date on the age of the fossil.

These methods use Radiometric dating to work out the age, which works on the fact that radioactive isotopes decay (lose their radioactivity) in a predictable way over a long period of time. The half-life of the isotope must be known.

* Radiocarbon (14C) - Measures the loss of the isotope carbon-14, taken up by organism when it was alive, kept in its fossilised remains. Useful with wood, shells, bone, animal tissue, soil etc between 90,000-1000 years.

* Potassium/Argon (K/Ar) - Measures the decay of potassium-40 to argon-40 in volcanic rocks that lie above or below fossil bearing strata. Useful with volcanic rocks and minerals between 100 million-5000 years.

* Fission