Quartenary Period The most recent period in Earth’s history: Pre-humans appeared at the beginning of this period, which also saw the rise (and fall) of giant mammals such as woolly mammoths. The last glacial ice sheets retreated during the last 20,000 years of this period. Paleogene-Neogene Periods The earliest grasses appeared at the beginning of the Paleogene, which followed the mass extinction of dinosaurs. These grasses allowed mammals to flourish during the Neogene, when grazing animals and the carnivores that hunted them were bountiful. Cretaceous Period This long period of 75 million years saw the earliest flowering plants. The dinosaurs ruled the land and skies during this time, but would die suddenly with an asteroid strike 65.5 million years ago, ending the period. Jurassic Period Everyone knows of Jurassic Park: The Jurassic Period was a time of abundant dinosaurs and ammonoids, a shelled sea creature. The first birds, relatives of dinosaurs, appeared toward the end of the Jurassic. Triassic Period The Triassic began following the Permian extinction, which wiped out 90% of life on Earth. The Triassic saw the rise of the dinosaurs and the first mammals. Permian Period The Permian was an age of abundant reptiles and mammal-like reptiles. The trilobites, which had lived on Earth for 250 million years, would go extinct at the end of the Permian. Carboniferous Period This period following the Devonian was a lush age of dense forests (which today form coal). The earliest reptiles appeared during the Carboniferous, and amphibians were abundant during this time. Devonian Period Though the Devonian saw the extinctions of many marine organisms, the period saw many firsts: this was a time of Earth’s first sharks, first amphibians, and the first forests—which would seed the Carboniferous period. Silurian Period The Silurian was a time of warm shallow seas. Silurian fossils show extensive coral reefs and the first fish with jaws. Followed by the Devonian, the Silurian saw the first land plants and animals, including flying insects. Ordivician Period During the Ordivician, which came before the Silurian, life still lived in the sea. The period is best known for its diverse marine invertebrates, including trilobites. The first corals and primitive fish appeared during this time, Cambrian Period The Cambrian marked the explosion of complex life in the oceans 542 million years ago. Major groups of animals appear in the fossil record, including the trilobites. It was followed by the Ordivician.