When Did Animals First Appear On Earth

New Scientist Default Image — Galapagos tortoises are the product of over iii billion years of evolution

Andy Rouse / Getty

There are all sorts of ways to reconstruct the history of life on Earth. Pinning downwardly when specific events occurred is often catchy, though. For this, biologists depend mainly on dating the rocks in which fossils are institute, and past looking at the "molecular clocks" in the Deoxyribonucleic acid of living organisms.

There are issues with each of these methods. The fossil record is like a movie with almost of the frames cut out. Because it is so incomplete, it can be difficult to establish exactly when particular evolutionary changes happened.

Mod genetics allows scientists to mensurate how different species are from each other at a molecular level, and thus to judge how much fourth dimension has passed since a unmarried lineage divide into unlike species. Confounding factors rack upwards for species that are very distantly related, making the before dates more uncertain.

These difficulties hateful that the dates in the timeline should be taken every bit approximate. Equally a general rule, they become more uncertain the further back along the geological timescale we look. Dates that are very uncertain are marked with a question mark.

3.viii billion years ago?

This is our current "all-time guess" for the beginning of life on Earth. It is distinctly possible that this date will modify equally more than bear witness comes to light. The first life may have developed in undersea alkaline vents, and was probably based on RNA rather than Dna.

At some betoken far back in time, a common ancestor gave rise to 2 main groups of life: bacteria and archaea.

How this happened, when, and in what order the different groups divide, is still uncertain.

3.5 billion years ago

The oldest fossils of single-celled organisms date from this time.

3.46 billion years ago

Some single-celled organisms may be feeding on methane by this time.

iii.4 billion years ago

Rock formations in Western Australia, that some researchers claim are fossilised microbes, appointment from this menses.

3 billion years agone

Viruses are nowadays by this time, merely they may be equally old every bit life itself.

2.iv billion years agone

The "great oxidation event". Supposedly, the poisonous waste material produced by photosynthetic cyanobacteria – oxygen – starts to build up in the atmosphere. Dissolved oxygen makes the atomic number 26 in the oceans "rust" and sink to the seafloor, forming striking banded iron formations.

Recently, though, some researchers have challenged this thought. They call back cyanobacteria only evolved afterward, and that other bacteria oxidised the fe in the absence of oxygen.

Even so others think that cyanobacteria began pumping out oxygen as early as 2.1 billion years ago, but that oxygen began to accumulate just due to some other cistron, mayhap a decline in methane-producing leaner. Methane reacts with oxygen, removing it from the atmosphere, and then fewer methane-belching bacteria would allow oxygen to build up.

ii.3 billion years agone

World freezes over in what may have been the first "snowball Earth", possibly as a result of a lack of volcanic activity. When the ice somewhen melts, it indirectly leads to more oxygen beingness released into the atmosphere.

2.15 billion years ago

First undisputed fossil evidence of blue-green alga, and of photosynthesis: the ability to take in sunlight and carbon dioxide, and obtain energy, releasing oxygen as a past-product.

There is some evidence for an earlier date for the beginning of photosynthesis, simply it has been called into question.

two billion years ago?

Eukaryotic cells – cells with internal "organs" (known as organelles) – come up into being. One key organelle is the nucleus: the control eye of the cell, in which the genes are stored in the form of DNA.

Eukaryotic cells evolved when one simple jail cell engulfed some other, and the two lived together, more or less amicably – an example of "endosymbiosis". The engulfed bacteria eventually become mitochondria, which provide eukaryotic cells with energy. The last common ancestor of all eukaryotic cells had mitochondria – and had as well developed sexual reproduction.

Subsequently, eukaryotic cells engulfed photosynthetic bacteria and formed a symbiotic relationship with them. The engulfed bacteria evolved into chloroplasts: the organelles that give green plants their colour and allow them to extract energy from sunlight.

Different lineages of eukaryotic cells acquired chloroplasts in this fashion on at least three split up occasions, and one of the resulting prison cell lines went on to evolve into all dark-green algae and dark-green plants.

1.5 billion years agone?

The eukaryotes divide into three groups: the ancestors of modernistic plants, fungi and animals split into separate lineages, and evolve separately. Nosotros practise non know in what lodge the iii groups broke with each other. At this fourth dimension they were probably all however single-celled organisms.

900 one thousand thousand years agone?

The kickoff multicellular life develops around this time.

It is unclear exactly how or why this happens, only one possibility is that single-celled organisms go through a stage similar to that of modernistic choanoflagellates: single-celled creatures that sometimes grade colonies consisting of many individuals. Of all the unmarried-celled organisms known to exist, choanoflagellates are the most closely related to multicellular animals, lending back up to this theory.

800 million years agone

The early on multicellular animals undergo their first splits. Beginning they divide into, essentially, the sponges and everything else – the latter being more formally known equally the Eumetazoa.

Effectually 20 1000000 years afterwards, a modest group called the placozoa breaks away from the rest of the Eumetazoa. Placozoa are sparse plate-like creatures about 1 millimetre across, and consist of only three layers of cells. It has been suggested that they may actually be the last common ancestor of all the animals.

770 meg years agone

The planet freezes over again in another "snowball Earth".

730 one thousand thousand years ago

The rummage jellies (ctenophores) split from the other multicellular animals. Similar the cnidarians that will shortly follow, they rely on water flowing through their body cavities to acquire oxygen and food.

680 meg years agone

The ancestor of cnidarians (jellyfish and their relatives) breaks abroad from the other animals – though there is equally yet no fossil prove of what information technology looks like.

630 million years ago

Around this time, some animals evolve bilateral symmetry for the first time: that is, they now have a defined superlative and bottom, as well as a front and back.

Piddling is known about how this happened. However, small worms chosen Acoela may be the closest surviving relatives of the first e'er bilateral creature. Information technology seems likely that the outset bilateral fauna was a kind of worm. Vernanimalcula guizhouena, which dates from around 600 million years agone, may exist the primeval bilateral animal constitute in the fossil record.

590 meg years ago

The Bilateria, those animals with bilateral symmetry, undergo a profound evolutionary split. They divide into the protostomes and deuterostomes.

The deuterostomes somewhen include all the vertebrates, plus an outlier grouping called the Ambulacraria. The protostomes go all the arthropods (insects, spiders, venereal, shrimp and then forth), various types of worm, and the microscopic rotifers.

Neither may seem like an obvious "group", only in fact the two can exist distinguished by the style their embryos develop. The first hole that the embryo acquires, the blastopore, forms the anus in deuterostomes, but in protostomes it forms the rima oris.

580 million years ago

The primeval known fossils of cnidarians, the group that includes jellyfish, sea anemones and corals, appointment to around this time – though the fossil bear witness has been disputed.

575 meg years ago

Strange life forms known as the Ediacarans announced around this time and persist for about 33 million years.

570 million years ago

A small-scale grouping breaks abroad from the main group of deuterostomes, known as the Ambulacraria. This grouping eventually becomes the echinoderms (starfish, brittle stars and their relatives) and two worm-like families chosen the hemichordates and Xenoturbellida.

Another echinoderm, the bounding main lily, is idea to be the "missing link" between vertebrates (animals with backbones) and invertebrates (animals without backbones), a carve up that occurred around this fourth dimension.

565 million years ago

Fossilised fauna trails propose that some animals are moving under their ain power.

540 million years ago

As the first chordates – animals that take a backbone, or at least a primitive version of it – sally among the deuterostomes, a surprising cousin branches off.

The ocean squirts (tunicates) begin their history as polliwog-like chordates, but metamorphose partway through their lives into lesser-domicile filter feeders that await rather similar a bag of seawater anchored to a rock. Their larvae still wait similar tadpoles today, revealing their close relationship to backboned animals.

535 meg years agone

The Cambrian explosion begins, with many new trunk layouts appearing on the scene – though the seeming rapidity of the appearance of new life forms may but be an illusion acquired by a lack of older fossils.

530 million years agone

The outset true vertebrate – an animal with a backbone – appears. It probably evolves from a jawless fish that has a notochord, a stiff rod of cartilage, instead of a truthful backbone. The starting time vertebrate is probably quite like a lamprey, hagfish or lancelet.

Effectually the same fourth dimension, the start clear fossils of trilobites appear. These invertebrates, which look like oversized woodlice and abound to 70 centimetres in length, proliferate in the oceans for the adjacent 200 million years.

520 one thousand thousand years ago

Conodonts, another contender for the title of "earliest vertebrate", appear. They probably wait like eels.

500 million years ago

Fossil show shows that animals were exploring the land at this fourth dimension. The offset animals to do so were probably euthycarcinoids – thought to be the missing link betwixt insects and crustaceans. Nectocaris pteryx, idea to be the oldest known ancestor of the cephalopods – the grouping that includes squid – lives effectually this time.

489 million years ago

The Great Ordovician Biodiversification Event begins, leading to a peachy increase in diversity. Inside each of the major groups of animals and plants, many new varieties appear.

465 million years agone

Plants begin colonising the state.

460 million years ago

Fish carve up into two major groups: the bony fish and cartilaginous fish. The cartilaginous fish, as the proper name implies, accept skeletons made of cartilage rather than the harder os. They eventually include all the sharks, skates and rays.

440 million years ago

The bony fish split into their two major groups: the lobe-finned fish with bones in their fleshy fins, and the ray-finned fish. The lobe-finned fish eventually give rise to amphibians, reptiles, birds and mammals. The ray-finned fish thrive, and give rise to nearly fish species living today.

The common antecedent of lobe-finned and ray-finned fish probably has simple sacs that function every bit primitive lungs, allowing it to gulp air when oxygen levels in the h2o fall too low. In ray-finned fish, these sacs evolve into the swim bladder, which is used for controlling buoyancy.

425 million years ago

The coelacanth, i of the most famous "living fossils" – species that have apparently not changed for millions of years – splits from the balance of the lobe-finned fish.

417 million years ago

Lungfish, some other legendary living fossil, follow the coelacanth past splitting from the other lobe-finned fish. Although they are unambiguously fish, complete with gills, lungfish take a pair of relatively sophisticated lungs, which are divided into numerous smaller air sacs to increase their surface area. These allow them to exhale out of h2o and thus to survive when the ponds they live in dry out.

400 one thousand thousand years agone

The oldest known insect lives around this time. Some plants evolve woody stems.

397 1000000 years ago

The start iv-legged animals, or tetrapods, evolve from intermediate species such equally Tiktaalik, probably in shallow freshwater habitats.

The tetrapods continue to conquer the state, and requite rise to all amphibians, reptiles, birds and mammals.

385 million years ago

The oldest fossilised tree dates from this period.

375 million years ago

Tiktaalik, an intermediate between fish and 4-legged land animals, lives around this time. The fleshy fins of its lungfish ancestors are evolving into limbs.

340 million years ago

The first major split occurs in the tetrapods, with the amphibians branching off from the others.

310 1000000 years ago

Inside the remaining tetrapods, the sauropsids and synapsids dissever from ane some other. The sauropsids include all the mod reptiles, plus the dinosaurs and birds. The start synapsids are besides reptiles, but accept distinctive jaws. They are sometimes called "mammal-like reptiles", and eventually evolve into the mammals.

320 to 250 million years agone

The pelycosaurs, the showtime major group of synapsid animals, dominate the land. The almost famous example is Dimetrodon, a large predatory "reptile" with a sail on its dorsum. Despite appearances, Dimetrodon is non a dinosaur.

275 to 100 million years ago

The therapsids, close cousins of the pelycosaurs, evolve alongside them and eventually supercede them. The therapsids survive until the early Cretaceous, 100 million years ago. Well before that, a group of them chosen the cynodonts develops dog-similar teeth and eventually evolves into the start mammals.

250 million years agone

The Permian flow ends with the greatest mass extinction in Globe'due south history, wiping out nifty swathes of species, including the last of the trilobites.

Every bit the ecosystem recovers, it undergoes a fundamental shift. Whereas earlier 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 effectually this fourth dimension. Several groups of reptiles colonise the seas, developing into the cracking marine reptiles of the dinosaur era.

210 million years ago

Bird-like footprints and a desperately-preserved fossil chosen Protoavis propose that some early on dinosaurs are already evolving into birds at this time. This merits remains controversial.

200 million years ago

As the Triassic catamenia comes to an terminate, another mass extinction strikes, paving the way for the dinosaurs to accept over from their sauropsid cousins.

Around the aforementioned fourth dimension, proto-mammals evolve warm-bloodedness – the ability to maintain their internal temperature, regardless of the external conditions.

180 million years ago

The first split occurs in the early mammal population. The monotremes, a group of mammals that lay eggs rather than giving nascency to live young, suspension apart from the others. Few monotremes survive today: they include the duck-billed platypus and the echidnas.

168 million years ago

A half-feathered, flightless dinosaur called Epidexipteryx, which may be an early step on the road to birds, lives in China.

150 one thousand thousand years agone

Archaeopteryx, the famous "get-go bird", lives in Europe.

140 million years agone

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 pocket-size, merely nourish them in a pouch for the first few weeks or months of their lives.

The bulk of modernistic marsupials live in Australia, but they reach information technology by an extremely roundabout road. Arising in s-east Asia, they spread into n America (which was attached to Asia at the time), then to south America and Antarctica, earlier making the concluding journey to Australia about fifty million years ago.

131 meg years ago

Eoconfuciusornis, a bird rather more advanced than Archaeopteryx, lives in Prc.

130 one thousand thousand years ago

The first flowering plants sally, following a period of rapid development.

105-85 1000000 years ago

The placental mammals separate into their 4 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 now.

100 1000000 years ago

The Cretaceous dinosaurs reach their peak in size. The giant sauropod Argentinosaurus, believed to be the largest land fauna in Earth's history, lives around this time.

93 million years ago

The oceans become starved of oxygen, possibly due to a huge underwater volcanic eruption. Twenty-seven per cent of marine invertebrates are wiped out.

75 meg years ago

The ancestors of modernistic primates divide from the ancestors of modern rodents and lagomorphs (rabbits, hares and pikas). The rodents proceed to exist astonishingly successful, eventually making up around 40 per cent of modern mammal species.

70 one thousand thousand years ago

Grasses evolve – though it volition exist several million years before the vast open up grasslands announced.

65 1000000 years ago

The Cretaceous-Third (K/T) extinction wipes out a swathe of species, including all the behemothic reptiles: the dinosaurs, pterosaurs, ichthyosaurs and plesiosaurs. The ammonites are also wiped out. The extinction clears the way for the mammals, which go on to boss the planet.

63 million years ago

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.

58 million years ago

The tarsier, a primate with enormous eyes to help information technology see at night, splits from the rest of the haplorrhines: the showtime to do so.

55 million years ago

The Palaeocene/Eocene extinction. A sudden ascent in greenhouse gases sends temperatures soaring and transforms the planet, wiping out many species in the depths of the bounding main – though sparing species in shallow seas and on state.

50 million years ago

Artiodactyls, which expect like a cross between a wolf and a tapir, begin evolving into whales.

48 million years ago

Indohyus, another possible ancestor of whales and dolphins, lives in Bharat.

47 million years agone

The famous fossilised primate known as "Ida" lives in northern Europe. Early whales called protocetids live in shallow seas, returning to land to give nascency.

40 million years ago

New Globe monkeys become the first simians (higher primates) to diverge from the rest of the group, colonising South America.

25 one thousand thousand years ago

Apes split from the One-time World monkeys.

18 1000000 years ago

Gibbons become the first ape to carve up from the others.

14 meg years ago

Orang-utans branch off from the other neat apes, spreading across southern Asia while their cousins remain in Africa.

7 million years ago

Gorillas branch off from the other slap-up apes.

6 million years ago

Humans diverge from their closest relatives; the chimpanzees and bonobos.

Shortly afterwards, hominins brainstorm walking on two legs. See our interactive timeline of human evolution for the full story of how modern humans developed.

two million years ago

A 700-kilogram rodent called Josephoartigasia monesi lives in South America. It is the largest rodent known to have lived, displacing the previous record holder: a behemothic guinea pig.

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