Fig. 5.2, p. 86 from Ancient Earth, Ancient Skies, by Brent G. Dalyrmple, shows the locations of some of Earth’s oldest rocks.
Understanding Evolution from UC Berkeley's Museum of Paleontology
The Tree of Life Project
ChronoZoom; Biological, Terrestrial, and Cosmological Evolution
Writings by Charles Darwin
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In some species, males engage in complex competitive behaviors, which in many cases necessitate growth of elaborate ornamental horns.
In 1837, Darwin sketched this evolutionary tree, his first that we know of.