A study of incomplete fossil records

Any scholar of history knows that the further back in time you go seeking answers, the more sparse and unreliable the clues. Paleontology is the study of the history of life, and its clues — for the most part — take the form of fossils. The fossil record is notoriously incomplete, but in general, we have more direct evidence of life in the recent past than we do of life in the most distant past.

Defining a species

A species is often defined as a group of individuals that actually or potentially interbreed in nature. In this sense, a species is the biggest gene pool possible under natural conditions.

Defining Speciation

Speciation is a lineage-splitting event that produces two or more separate species. Imagine that you are looking at a tip of the tree of life that constitutes a species of fruit fly. Move down the phylogeny to where your fruit fly twig is connected to the rest of the tree. That branching point, and every other branching point on the tree, is a speciation event. At that point genetic changes resulted in two separate fruit fly lineages, where previously there had just been one lineage. But why and how did it happen?

How do you know how old it is? (Radiometric dating, stratigraphy & molecular clocks)