10 billion years ago. Our galaxy, the Milky Way, emerges. It now contains c. 10 billion stars. 4.5 billion years ago. Our solar system--sun, planets, asteroids, and comets--is the process of forming. Biological evolution: 3.5 to 3.8 billion years ago. The earliest evidence for life, microbial (procaryotic cells, similar to very simple bacteria) dates back to this period. 2 billion years ago. Cells with nuclei have by now appeared. 1.7 billion years ago. The earliest known multicellular organisms have appeared. 1.6 billion years ago. The oldest known animal fossils date back to this period. 540 million years ago: Shell-bearing animals have appeared. Then, the order goes as follows: 490 million years ago: Vertebrates (simple fishes). 375 million years ago. Tiktaalik roseae, disovered in 2004, provided a missing evolutionary link between fish and the first animals. The new species walked out of water onto land, in effect, about 375 million years ago. Morelle, Rebecca. "Arctic fossils mark move to land." 5 April BBC News. BBC. News.

"What has the head of a crocodile and the gills of a fish? "May 2006 Tiktaalik, of course. Pronounced tik-TAA-lik, this 375 million year old fossil splashed across headlines as soon as its discovery was announced in April of Unearthed in Arctic Canada by a team of researchers led by Neil Shubin, Edward Daeschler, and Farish Jenkins, Tiktaalik is technically a fish, complete with scales and gills — but it has the flattened head of a crocodile and unusual fins. Its fins have thin ray bones for paddling like most fishes', but they also have sturdy interior bones that would have allowed Tiktaalik to prop itself up in shallow water and use its limbs for support as most four-legged animals do. Those fins and a suite of other characteristics set Tiktaalik apart as something special; it has a combination of features that show the evolutionary transition between swimming fish and their descendents, the four-legged vertebrates — a clade which includes amphibians, dinosaurs, birds, mammals, and of course, humans." alikA reconstruction of Tiktaalik alongside a cast of its fossil, and a map showing where the fossil was found, on Ellesmere Island, Nunavut, Canada. This site is a collaborative project of the University of California Museum of Paleontology and the National Center for Science of California Museum of PaleontologyNational Center for Science

350 million years ago: Amphibians. 310 millioin years ago: Reptiles. 200 million years ago. Mammals. 95 million years ago. Haasiophis terrasanctus, a snake with legs, has evolved. 60 million years ago. Nonhuman primates. 50 million years ago. The ancestors of whales and dolphins are four-footed land animals, comparable to dogs, that share a common ancestor with hippos, camels and deer They return to the water. 35 million years ago. Ancient whales by then have finally lost the last remnants of their legs. 25 million years ago: The earliest apes. Gorillas are the next closet relatives to humans after than chimpanzees. 20 million years ago: The lesser apes, such as the gibbons, diverge million years ago: "The Asian great apes (the orangutan being the only surviving form) diverge from the African hominoids...." (NAS). 8 million years ago: The ancestral lines of gorillas diverge. 6 million years ago: Orrorin tugenensis, about the size of a modern chimpanzee, may be one of the earliest human ancestors on record. 5 million years ago: Chimpanzees diverge. Image of present-day chimp below: