A Brief History of Prehistory

4.1 billion years ago, Archean eon.

The very first life, probably some self-replicating molecule, evolves. It probably wasn’t DNA, but some precursor, like RNA.

541 million years ago, Cambrian period.

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During a time called the Cambrian Explosion, life expands with an amazing diversity. The very first super predator, Anomalocaris rules the oceans. Also new are the first trilobites (although we think their ancestors existed earlier on in the Precambrian). Trilobites are a common (but now extinct) group of arthropods related to horseshoe crabs that were extremely common in the Palaeozoic. This is the first period of the Palaeozoic era.

488.3 million years ago, Ordovician period.

More life forms evolve, including a gigantic squid with a cone-shaped shell the size of a bus called Cameroceras. At the end of the Ordovician is the Ordovician Mass Extinction Event.

443 million years ago, Silurian.

Eurypterids

 

Continental land masses are low and sea levels are rising. Eurypterids (sea scorpions) are in the sea.

416 million years ago, Devonian period.

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Tiktaalik is a fish that decided to take a step onto land. This is the very first vertebrate to explore the land and is a transitional species (or missing link) between fish and amphibians. Meanwhile, plants are flourishing on land for the first time and giant armour-plated fish like Dunkleosteus swim in the oceans. Sharks appear around here. At the end of the Devonian is the Late Devonian mass extinction event. From this point onwards, trilobites start to go into a decline.

359.2 million years ago, Carboniferous period.

In this time much of the world was covered in swamps and oxygen levels were higher than they are today. Things that look like trees but are actually giant ferns tower over the landscape, and over time these turn into the coal we use today. Due to high oxygen levels, giant bugs rule the world.

229 million years ago, Permian period.

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The world is one big supercontinent, Pangea. The ancestors of mammals, or synapsids, are evolving. These include the not-so-sail-backed Dimetrodon and the sabre-toothed Inostrancevia. These are not true mammals, though. At the very end of the Permian was a gigantic mass extinction that killed a grand total of 96% of life on Earth, finishing off the last of the trilobites. This is the Permian – Triassic extinction event.

250 million years ago, Triassic period.

 

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The first period of the Mesozoic Era, the Triassic heralded the arrival of many new major groups of animals. These include the first archosaurs, or ‘ruling lizards’, a group that included the first crocodylomorphs, the first rauisuchians, the first pterosaurs and the first dinosaurs. Eoraptor was the very first dinosaur, a small two-legged animal. Some say that feathers originated here but others believe that feathers evolved independently in different dinosaur groups. At the end of the Triassic is the Triassic-Jurassic extinction event.

199.6 million years ago, Jurassic period.

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This is the start of the golden age of the dinosaurs. Sauropods, the long-necked dinosaurs, dominate as well as many other dinosaur groups including ornithischians and theropods. Ornithischians are a group of dinosaurs that include ceratopsians, stegosaurs and most of the herbivorous dinosaurs apart from sauropods. Theropods were the majority of the two-legged dinosaurs and the majority of them ate meat (but some didn’t). Pterosaurs rule the air and an assortment of marine reptiles swim the depths, but neither are dinosaurs. These marine reptiles include the fish-like ichthyosaurs and the long-necked plesiosaurs. Archaeopteryx is a transitional species, or ‘missing link’, between dinosaurs and birds. The continent Pangea has broken into two separate continents – Laurasia and Gondwana. Early mammals emerge in the shadows.

145 million years ago, Cretaceous period.

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Birds are everywhere. Mammals are emerging. Flowers appear. Plesiosaurs and Ichthyosaurs are replaced by Mosasaurs. The biggest land animal ever, Argentinosaurus, a sauropod that lived in South America is plodding along, whilst in North Africa, the longest meat-eating dinosaur ever, Spinosaurus, is swimming in the rivers. In North, America Tyrannosaurus is fighting with Triceratops, a horned ceratopsian dinosaur. Other major dinosaur groups include abelisaurs, the dominant predators of the Southern continents, dromaeosaurs, the infamous raptors, ankylosaurs, the armoured tanks of the dinosaur age, hadrosaurs, the duck-billed dinosaurs, and pachycephalosaurs, the hard-headed herbivores. At the end of the Cretaceous, the climate starts to get hotter as supervolcanoes start erupting in India, and the K-T mass extinction event begins. As dinosaurs are on their last feet, a huge asteroid the size of Mount Everest comes and blows everyone up. Pterosaurs, non-avian dinosaurs and 75% of life on Earth die.

65.5 million years ago, Palaeocene epoch.

Life starts recovering. With the major land animals gone, many niches are open. It hangs in the balance whether birds or mammals will inherit the world. In the end, it goes to the mammals. This is the first epoch in the Cenozoic era.

56 million years ago, Eocene epoch.

 

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Hoofed mammals appear, including Eohippus, the first horse, and the ancestors to rhinos and tapirs. Grasses encourage the evolution of grazing animals. In the oceans, whales are evolving and some, like Basilosaurus, are ferocious killers.

33.9 million years ago, Oligocene epoch.

During this time the world started cooling, making it possible for the first time for glaciers to form in the poles. Also, grasslands are expanding, resulting in the shrinking of forests. Many herbivores evolve to run fast and predators learn to stalk their prey through the grass. The biggest land mammal ever, Pacaceratherium, is plodding along.

23 million years ago, Miocene epoch.

In America, there are pig-like creatures called entelodontids that look like they were loose from hell whilst in Africa there are giant elephants with downwards-facing tusks called Deinotherium. In the sea is the largest shark ever: the 17- metre C.megalodon.

5.3 million years ago, Pliocene epoch.

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This is the time of sabre-toothed cats (Smilodon), tank-sized armadillos (Glyptodon) and giant ground sloths (Megatherium). The continents are now in the arrangements that they are today. In Africa is Australopithecus, the ape ancestor of humans.

1.8 million years ago, Pleistocene epoch.

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These are the ice ages, the time of mammoths, the appearance of our genus; Homo,  and woolly rhinos. There are spans of warm and cold when the glaciers come down from the poles before shrinking again. Sea levels shrink and in some parts of the world weird megafauna rules.

11,500 thousand years ago, Holocene epoch.

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During a brief span of warmth the species Homo sapiens colonises the globe. We are currently living in the Holocene. Others say that we are living in a new period, the Anthropocene, as the main characteristic of this age is the global changes made by the activity of humans.

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