[[Image:PIA02405.jpg|thumb|For most of Earth’s history, there were no multicellular organisms on land. Parts of the surface may have vaguely resembled this view of [[Mars]].]]

Oxygen accumulation from photosynthesis resulted in the formation of an ozone layer that absorbed much of Sun’s [[ultraviolet radiation]], meaning unicellular organisms that reached land were less likely to die, and prokaryotes began to multiply and become better adapted to survival out of the water. [[Prokaryotes]] had probably colonized the land as early as 2.6 Ga even before the origin of the eukaryotes. For a long time, the land remained barren of multicellular organisms. The supercontinent [[Pannotia]] formed around 600 [[annum|Ma]] and then broke apart a short 50 million years later. Fish, the [[prehistoric fish|earliest vertebrates]], evolved in the oceans around 530 Ma. A major [[Cambrian–Ordovician extinction events|extinction event]] occurred near the end of the Cambrian period, which ended 488 Ma.

Several hundred million years ago, plants (probably resembling [[algae]]) and fungi started growing at the edges of the water, and then out of it. The oldest fossils of land fungi and plants date to 480–460 Ma, though molecular evidence suggests the fungi may have colonized the land as early as 1000 Ma and the plants 700 Ma. Initially remaining close to the water’s edge, mutations and variations resulted in further colonization of this new environment. The timing of the first animals to leave the oceans is not precisely known: the oldest clear evidence is of [[arthropod]]s on land around 450 Ma, perhaps thriving and becoming better adapted due to the vast food source provided by the terrestrial plants. There is also some unconfirmed evidence that arthropods may have appeared on land as early as 530 Ma.

At the end of the [[Ordovician]] period, 440 Ma, additional [[Ordovician–Silurian extinction event|extinction events]] occurred, perhaps due to a concurrent [[ice age]]. Around 380 to 375 Ma, the first [[tetrapod]]s evolved from fish. It is thought that perhaps fins evolved to become limbs which allowed the first tetrapods to lift their heads out of the water to breathe air. This would let them survive in oxygen-poor water or pursue small prey in shallow water. They may have later ventured on land for brief periods. Eventually, some of them became so well adapted to terrestrial life that they spent their adult lives on land, although they hatched in the water and returned to lay their eggs. This was the origin of the [[amphibian]]s. About 365 Ma, another [[Late Devonian extinction|period of extinction]] occurred, perhaps as a result of global cooling. Plants evolved [[seed]]s, which dramatically accelerated their spread on land, around this time (by approximately 360 Ma).

[[Image:Pangaea continents.png|thumb|right|[[Pangaea]], the most recent supercontinent, existed from 300 to 180 Ma. The outlines of the modern continents and other land masses are indicated on this map.]]

Some 20 million years later (340 Ma), the [[amniotic egg]] evolved, which could be laid on land, giving a survival advantage to [[tetrapod]] embryos. This resulted in the divergence of [[amniote]]s from amphibians. Another 30 million years (310 Ma) saw the divergence of the [[synapsid]]s (including mammals) from the [[sauropsid]]s (including birds and reptiles). Other groups of organisms continued to evolve and lines diverged—in fish, insects, bacteria, and so on—but less is known of the details. 300 million years ago, the most recent hypothesized supercontinent formed, called [[Pangaea]].

The [[Permian–Triassic extinction event|most severe extinction event]] to date took place 250 Ma, at the boundary of the [[Permian]] and [[Triassic]] periods; 95% of life on Earth died out, possibly due to the [[Siberian Traps]] volcanic event. The discovery of the [[Wilkes Land crater]] in Antarctica may suggest a connection with the Permian-Triassic extinction, but the age of that crater is not known. But life persevered, and around 230 Ma, [[dinosaur]]s split off from their reptilian ancestors. An extinction event between the [[Triassic–Jurassic extinction event|Triassic and Jurassic periods]] 200 Ma spared many of the dinosaurs, and they soon became dominant among the vertebrates. Though some of the mammalian lines began to separate during this period, existing mammals were probably all small animals resembling [[shrew]]s.

By 180 Ma, Pangaea broke up into [[Laurasia]] and [[Gondwana]]. The boundary between avian and non-avian dinosaurs is not clear, but "[[Archaeopteryx]]", traditionally considered one of the first birds, lived around 150 Ma. The earliest evidence for the [[Flowering plant|angiosperms]] evolving flowers is during the [[Cretaceous]] period, some 20 million years later (132 Ma).

Competition with birds drove many [[pterosaur]]s to extinction and the dinosaurs were probably already in decline when, 65 Ma, a meteorite probably struck Earth just off the [[Yucatán Peninsula]] where the [[Chicxulub crater]] is today. This ejected vast quantities of particulate matter and vapor into the air that occluded sunlight, inhibiting photosynthesis. Most large animals, including the non-avian dinosaurs, [[Cretaceous–Tertiary extinction event|became extinct]], marking the end of the Cretaceous period and [[Mesozoic]] era. Thereafter, in the [[Paleocene]] epoch, mammals rapidly diversified, grew larger, and became the dominant vertebrates. Perhaps a couple of million years later (around 63 Ma), the last common ancestor of [[primate]]s lived. By the late [[Eocene]] epoch, 34 Ma, some terrestrial mammals had returned to the oceans to become animals such as "[[Basilosaurus]]" which later gave rise to [[dolphin]]s and [[baleen whale]]s.

Colonization of land
Proterozoic development of life
राक्षसी आघात
Rodinia and other supercontinents