It took less than two billion years for our Milky Way Galaxy to emerge from the chaos of the Hot Big Bang some 13.8 billion years ago. Another 7 billion years would elapse before our Sun and Solar System took form. During this time, the thermonuclear processing of matter in the cores of stars and during the violent deaths of massive stars collectively forged the heavy elements that characterize our rocky home planet.
On Earth’s moist surface, microbial life took hold less than a billion years after the Sun turned on. Yet another three billion years would have to pass, before multi-cellular life forms began to leave fossil records in the accumulating sediments of sand, mud, and limestone. The remaining 500 million years up to the present day have witnessed the successive flourishing of primitive sea animals, land animals, flowering plants, dinosaurs, mammals, and – in the last two million years – humans.
Timeline of Earth’s history, including the origin of microbial life 3.8 billion years ago and the evolution of multi-cellular life forms to the present day. Courtesy of Andree Valley (see http://www.geology.wisc.edu/zircon/Earliest%20Piece/Earliest.html ).
Homo sapiens began ...