611-546 BC Anaximander's most famous work, On Nature, summarizes his thoughts on the origin of the Earth and its life. Although the poem has not survived to this day, other authors have referred to excerpts from the work. From the parts of the poem that have been reconstructed, Anaximander believed that the Earth, part of an open universe, was originally a sphere covered in water. Plants and animals grew from the mud created when the Sun gradually dried up the water. Perhaps from the observation of fossils, Anaximander, a bit of a proto-evolutionist, concluded that humans developed from fish. This is a rudimentary start to evolutionary thinking. “For we are all born of earth and water. » Xenophanes, who studied under Anaximander, was interested in various fields, including poetry, philosophy and natural studies. He thought of an interconnected universe and saw clouds as the source of many natural phenomena. Xenophanes studied the fossils of ancient life forms, one of the first to do so, and came to some unique conclusions, including the idea that life began in an aquatic environment. “..the entire life process of the Earth takes place so gradually and over such different periods of time.