The age of fossils can be determined using isotopes. The fossil record traces the history of life on earth. The degree of relatedness between organisms is reflected in the similarity of their DNA base sequences.
Many diverse organisms show anatomical similarities, such as vertebrate forelimbs.
Similar structures that were inherited from a common ancestor are called homologous structures. The unity of plan seen in all vertebrates is evident in their common stages of embryological development. Vestigial structures are anatomical features that served a purpose in an ancestor but no longer have a function. Biogeography is the study of the distribution of plants and animals throughout the world. At one time, the major continents were joined in one landmass that eventually broke apart into the continents of today.