Life on earth began how long ago

The therapsids, close cousins of the pelycosaurs, evolve alongside them and eventually replace them. The therapsids survive until the early Cretaceous, million years ago. Well before that, a group of them called the cynodonts develops dog-like teeth and eventually evolves into the first mammals. As the ecosystem recovers, it undergoes a fundamental shift. Whereas before the synapsids first the pelycosaurs, then the therapsids dominated, the sauropsids now take over — most famously, in the form of dinosaurs.

The ancestors of mammals survive as small, nocturnal creatures. In the oceans, the ammonites , cousins of the modern nautilus and octopus, evolve around this time. Several groups of reptiles colonise the seas, developing into the great marine reptiles of the dinosaur era.

Bird-like footprints and a badly-preserved fossil called Protoavis suggest that some early dinosaurs are already evolving into birds at this time. This claim remains controversial. As the Triassic period comes to an end, another mass extinction strikes, paving the way for the dinosaurs to take over from their sauropsid cousins. Around the same time, proto-mammals evolve warm-bloodedness — the ability to maintain their internal temperature, regardless of the external conditions.

The first split occurs in the early mammal population. The monotremes, a group of mammals that lay eggs rather than giving birth to live young, break apart from the others. Few monotremes survive today: they include the duck-billed platypus and the echidnas. A half-feathered, flightless dinosaur called Epidexipteryx , which may be an early step on the road to birds, lives in China.

Around this time, placental mammals split from their cousins the marsupials. These mammals, like the modern kangaroo, that give birth when their young are still very small, but nourish them in a pouch for the first few weeks or months of their lives. The majority of modern marsupials live in Australia, but they reach it by an extremely roundabout route. Arising in south-east Asia , they spread into north America which was attached to Asia at the time , then to south America and Antarctica, before making the final journey to Australia about 50 million years ago.

Eoconfuciusornis , a bird rather more advanced than Archaeopteryx , lives in China. The first flowering plants emerge, following a period of rapid evolution. The placental mammals split into their four major groups: the laurasiatheres a hugely diverse group including all the hoofed mammals, whales, bats, and dogs , euarchontoglires primates, rodents and others , Xenarthra including anteaters and armadillos and afrotheres elephants, aardvarks and others.

Quite how these splits occurred is unclear at present. The Cretaceous dinosaurs reach their peak in size. The oceans become starved of oxygen , possibly due to a huge underwater volcanic eruption.

Twenty-seven per cent of marine invertebrates are wiped out. The ancestors of modern primates split from the ancestors of modern rodents and lagomorphs rabbits, hares and pikas. The rodents go on to be astonishingly successful, eventually making up around 40 per cent of modern mammal species. Grasses evolve — though it will be several million years before the vast open grasslands appear.

The ammonites are also wiped out. The extinction clears the way for the mammals, which go on to dominate the planet. The primates split into two groups, known as the haplorrhines dry-nosed primates and the strepsirrhines wet-nosed primates.

The strepsirrhines eventually become the modern lemurs and aye-ayes , while the haplorrhines develop into monkeys and apes — and humans. The tarsier, a primate with enormous eyes to help it see at night, splits from the rest of the haplorrhines: the first to do so.

A sudden rise in greenhouse gases sends temperatures soaring and transforms the planet, wiping out many species in the depths of the sea — though sparing species in shallow seas and on land. Artiodactyls, which look like a cross between a wolf and a tapir, begin evolving into whales. Indohyus , another possible ancestor of whales and dolphins , lives in India. Early whales called protocetids live in shallow seas, returning to land to give birth.

Also found in the Pilbara region are fossilised remains of stromatolites. These are also mat-like structures of microbes that live in shallow marine environments and are still around today.

Sand accumulates on top of the microbial mats, and the microbes move up towards the surface to get to the light again, making distinctive bulbous-shaped layers that eventually solidify into rocks. Although we know that some living things thrive in more extreme conditions, the combination of warmth and water seem to be the most likely requirements for creating an environment that can support some kind of life—at least, the kinds of life forms similar to what we find on Earth.

But who knows what other kinds of living things might exist? The origins of life on Earth Everything we know about life comes from a sample size of one: life here on Earth. The streaky artwork of masses of cyanobacteria blue-green algae.

So the window when life began was very short. As soon as life could have formed on our planet, it did. The answer may involve the collision of comets and asteroids with the Earth, since these objects contain abundant supplies of both water and carbon-based molecules. It boils down to three things. First, the organism has to keep itself together, often with an outer layer, the removal of which is immediately problematic. Second, it must feed itself. This involves complex chemical reactions.

And third, life has to reproduce itself, which means it must have genes it can pass on. The last 50 years of origin-of-life research were dominated by attempts to make one of these systems on its own: for instance, a genetic molecule that reproduced by copying itself.

The other bits were assumed to come later.