Changes

Thus we can now estimate that the rocks in which the earliest fossil microbes are found are about 3.5 billion years old, that the earliest known widespread fossil fauna of solid-bodied animals were laid down in the Cambrian sediments over 500 million years ago, the first bony fish appear some 440 million years ago, and so on. We can also date the appearance, long histories, and eventual extinction, of whole groups of species, most notably the trilobites.

Thus we can now estimate that the rocks in which the earliest fossil microbes are found are about 3.5 billion years old, that the earliest known widespread fossil fauna of solid-bodied animals were laid down in the Cambrian sediments over 500 million years ago, the first bony fish appear some 440 million years ago, and so on. We can also date the appearance, long histories, and eventual extinction, of whole groups of species, most notably the trilobites.

''Work in progress''

Very close similarities between species have always been observed. Specific details of living organisms serve quite different purposes, such as the jaw bones of certain fish, whose analogues in mammals are part of the inner ear. The presumption of a familial relation existed long before plausible mechanisms were understood and confirmed. Organized taxonomies, based on such homologous traits, drew attention to this persuasive though at the time mysterious evidence suggesting common descent.