611-546 BC Anaximander's most famous work, entitled On Nature, summarizes his thoughts on the origin of the Earth and his life. Although the poem has not survived to this day, other writers have referenced passages from the work. From the reconstructed parts of the poem, Anaximander believed that the Earth, part of an open universe, was born as a sphere covered by water. Plants and animals developed from the mud created as the Sun gradually dried up the water. Perhaps from the observation of fossils, Anaximander, a bit of a proto-evolutionist, concluded that humans had evolved from fish. This is a rudimentary beginning of evolutionary thinking. "Because we are all born of earth and water." Xenophanes, who studied under Anaximander, was interested in various fields, including poetry, philosophy, and nature study. He thought of an interconnected universe and considered clouds as the source of many natural phenomena. Xenophanes studied fossils of previous life, one of the first to do so, and drew unique conclusions, including the idea that life began in an aquatic environment. “...the whole life process of the earth happens so gradually and in such periods of time