a record of the different types of organisms that lived in the past

Where there is a geographical barrier - mountain, river, ocean or gorge in the way

Radioactive dating and tree rings

This is because natural selection is involved and selection can only act on variation that is already present in a population

Sediment sticks to the surface of the living algae, forming a crust. The algae grow through the sediment to form a new layer of living matter

DNA analysis

a common ancestor

Original, Replacement, Carbon film, indirect, petrification

Different groups of the population are prevented in some way from interbreeding

Once groups of populations are isolated, natural selection affects the genotype of each group, leads to changes that prevent groups from breeding

rainfall, temperature, salinity, ocean current, sunlight

Fossil record