Million years ago in the context of "Velociraptor"

Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins c. 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of symbols, marks, and images appears very early among humans, but the earliest known writing systems appeared c. 5,200 years ago. It took thousands of years for writing systems to be widely adopted, with writing having spread to almost all cultures by the 19th century. The end of prehistory therefore came at different times in different places, and the term is less often used in discussing societies where prehistory ended relatively recently. It is based on an old conception of history that without written records there could be no history. The most common conception today is that history is based on evidence, however the concept of prehistory has not been completely discarded.

In the early Bronze Age, Sumer in Mesopotamia, the Indus Valley Civilisation, and ancient Egypt were the first civilizations to develop their own scripts and keep historical records, with their neighbours following. Most other civilizations reached their end of prehistory during the following Iron Age. The three-age division of prehistory into Stone Age, Bronze Age, and Iron Age remains in use for much of Eurasia and North Africa, but is not generally used in those parts of the world where the working of hard metals arrived abruptly from contact with Eurasian cultures, such as Oceania, Australasia, much of Sub-Saharan Africa, and parts of the Americas. With some exceptions in pre-Columbian civilizations in the Americas, these areas did not develop writing systems before the arrival of Eurasians, so their prehistory reaches into relatively recent periods; for example, 1788 is usually taken as the end of the prehistory of Australia.

The Silurian-Devonian Terrestrial Revolution, also known as the Devonian Plant Explosion (DePE) and the Devonian explosion, was a period of rapid colonization, diversification and radiation of land plants (particularly vascular plants) and fungi (especially dikaryans) on dry lands that occurred 428 to 359 million years ago (Mya) during the Silurian and Devonian periods, with the most critical phase occurring during the Late Silurian and Early Devonian.

This diversification of terrestrial photosynthetic florae had vast impacts on the biotic composition of the Earth's surface, especially upon the Earth's atmosphere by oxygenation and carbon fixation. Their roots also eroded into the rocks, creating a layer of water-holding and mineral/organic matter-rich soil on top of Earth's crust known as the pedosphere, and significantly altering the chemistry of Earth's lithosphere and hydrosphere. The floral activities following the Silurian-Devonian plant revolution also exerted significant influences on changes in the water cycle and global climate, as well as driving the biosphere by creating diverse layers of vegetations that provide both sustenance and refuge for both upland and wetland habitats, paving the way for all terrestrial and aquatic biomes that would follow.

The Devonian (/dəˈvoʊni.ən, dɛ-/ də-VOH-nee-ən, deh-) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at 419.62 million years ago (Ma), to the beginning of the succeeding Carboniferous period at 358.86 Ma. It is the fourth period of both the Paleozoic and the Phanerozoic. It is named after Devon, South West England, where rocks from this period were first studied.

The first significant evolutionary radiation of life on land occurred during the Devonian, as free-sporing land plants (pteridophytes) began to spread across dry land, forming extensive coal forests which covered the continents. By the middle of the Devonian, several groups of vascular plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants (pteridospermatophytes) appeared. This rapid evolution and colonization process, which had begun during the Silurian, is known as the Silurian-Devonian Terrestrial Revolution. The earliest land animals, predominantly arthropods such as myriapods, arachnids and hexapods, also became well-established early in this period, after beginning their colonization of land at least from the Ordovician Period.

Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

Dinosaurs are varied from taxonomic, morphological and ecological standpoints. Birds, at over 11,000 living species, are among the most diverse groups of vertebrates. Using fossil evidence, paleontologists have identified over 900 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species (birds) and fossil remains. Through most of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded. Most research conducted since the 1970s, however, has indicated that dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. Some were herbivorous, others carnivorous. Evidence suggests that all dinosaurs were egg-laying, and that nest-building was a trait shared by many dinosaurs, both avian and non-avian.

The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.5 ± 1.0 to 143.1 ± 0.6 million years ago (Ma), which is preserved in Upper Jurassic strata.

In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age. In the past, Malm was also used to indicate the unit of geological time, but this usage is now discouraged to make a clear distinction between lithostratigraphic and geochronologic/chronostratigraphic units.

The Permian–Triassic extinction event, colloquially known as the Great Dying, was an extinction event that occurred approximately 251.9 million years ago (mya), at the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras. It is Earth's most severe known extinction event, with the extinction of 57% of biological families, 62% of genera, 81% of marine species, and 70% of terrestrial vertebrate species. It is also the greatest known mass extinction of insects. It is the greatest of the "Big Five" mass extinctions of the Phanerozoic. There is evidence for one to three distinct pulses, or phases, of extinction.

The scientific consensus is that the main cause of the extinction was the flood basalt volcanic eruptions that created the Siberian Traps, which released sulfur dioxide and carbon dioxide, resulting in euxinia (oxygen-starved, sulfurous oceans), elevated global temperatures,and acidified oceans.The level of atmospheric carbon dioxide rose from around 400 ppm to 2,500 ppm with approximately 3,900 to 12,000 gigatonnes of carbon being added to the ocean-atmosphere system during this period.

The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales with teeth, such as beaked whales and the sperm whales. 73 species of toothed whales are described. They are one of two living groups of cetaceans, with the other being the baleen whales (Mysticeti), which have baleen instead of teeth. The two groups are thought to have diverged around 34 million years ago (mya).

Toothed whales range in size from the 1.4 m (4 ft 7 in) and 54 kg (119 lb) vaquita to the 20 m (66 ft) and 100 t (98 long tons; 110 short tons) sperm whale. Several species of odontocetes exhibit sexual dimorphism, in that there are size or other morphological differences between females and males. They have streamlined bodies and two limbs that are modified into flippers. Some can travel at up to 30 knots. Odontocetes have conical teeth designed for catching fish or squid. They have well-developed hearing that is adapted for both air and water, so much so that some can survive even if they are blind. Some species are well adapted for diving to great depths. Almost all have a layer of fat, or blubber, under the skin to keep warm in the cold water, with the exception of river dolphins.

The Hadean (/heɪˈdiːən, ˈheɪdiən/ hay-DEE-ən, HAY-dee-ən) is the first and oldest of the four geologic eons of Earth's history, starting with the planet's formation about 4.6 Ga (estimated 4567.30 ± 0.16 Ma set by the age of the oldest solid material in the Solar System—protoplanetary disk dust particles—found as chondrules and calcium–aluminium-rich inclusions in some meteorites about 4.567 Ga), and ending 4.031 Ga, the age of the oldest known intact rock formations on Earth as recognized by the International Commission on Stratigraphy. The interplanetary collision that created the Moon occurred early in this eon. The Hadean eon was succeeded by the Archean eon, with the Late Heavy Bombardment hypothesized to have occurred at the Hadean-Archean boundary.

Hadean rocks are very rare, largely consisting of granular zircons from one locality (Jack Hills) in Western Australia. Hadean geophysical models remain controversial among geologists: plate tectonics and the growth of cratons into continents may have started in the Hadean, but there is still uncertainty.

The Neoproterozoic Oxygenation Event (NOE), also called the Second Great Oxidation Event, was a geologic time interval between around 850 and 540 million years ago during the Neoproterozoic era, during which the oxygen concentration in Earth's atmosphere and oceans rose significantly. Taking place after the end to the Boring Billion, a euxinic period of extremely low atmospheric oxygen spanning from the Statherian period of the Paleoproterozoic era to the Tonian period of the Neoproterozoic era, the NOE was the second major increase in atmospheric and oceanic oxygen concentration on Earth, though it was not as prominent as the Great Oxidation Event (GOE) of the Neoarchean-Paleoproterozoic boundary. Unlike the GOE, it is unclear whether the NOE was a synchronous, global event or a series of asynchronous, regional oxygenation intervals with unrelated causes.

The Ediacaran ( /ˌiːdiˈækərən, ˌɛdi-/ EE-dee-AK-ər-ən, ED-ee-) is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.

The Ediacaran Period is named after the Ediacara Hills of South Australia, where trace fossils of a diverse community of previously unrecognized lifeforms (later named the Ediacaran biota) were first discovered by geologist Reg Sprigg in 1946. Its status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years. Although the period took namesake from the Ediacara Hills in the Nilpena Ediacara National Park, the type section is actually located in the bed of the Enorama Creek within the Brachina Gorge in the Ikara-Flinders Ranges National Park, at 31°19′53.8″S 138°38′0.1″E / 31.331611°S 138.633361°E / -31.331611; 138.633361, approximately 55 km (34 mi) southeast of the Ediacara Hills fossil site.

The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch made up of two stages: the Tortonian and Messinian. It lasted from 11.63 Ma (million years ago) to 5.333 Ma.

Homo habilis (lit. 'handy man') is an extinct species of archaic human from the Early Pleistocene of East and South Africa about 2.4 million years ago to 1.65 million years ago (mya). It is among the oldest species of archaic humans. Suggestions for pushing back the age to 2.8 Mya were made in 2015 based on the discovery of a jawbone. Upon species description in 1964, H. habilis was highly contested, with many researchers recommending it be synonymised with Australopithecus africanus, the only other early hominin known at the time, but H. habilis received more recognition as time went on and more relevant discoveries were made. By the 1980s, H. habilis was proposed to have been a human ancestor, directly evolving into Homo erectus, which directly led to modern humans. This viewpoint is now debated. Several specimens with insecure species identification were assigned to H. habilis, leading to arguments for splitting, namely into "H. rudolfensis" and "H. gautengensis" of which only the former has received wide support.

H. habilis brain size generally varied from 500 to 900 cm (31–55 cu in). The body proportions of H. habilis are only known from two highly fragmentary skeletons, and is based largely on assuming a similar anatomy to the earlier australopithecines. Because of this, it has also been proposed H. habilis be moved to the genus Australopithecus as Australopithecus habilis. However, the interpretation of H. habilis as a small-statured human with inefficient long-distance travel capabilities has been challenged. The presumed female specimen OH 62 is traditionally interpreted as having been 100–120 cm (3 ft 3 in – 3 ft 11 in) in height and 20–37 kg (44–82 lb) in weight assuming australopithecine-like proportions, but assuming humanlike proportions she would have been about 148 cm (4 ft 10 in) and 35 kg (77 lb). Nonetheless, Homo habilis may have been at least partially arboreal like what is postulated for australopithecines. Early hominins are typically reconstructed as having thick hair and marked sexual dimorphism with males much larger than females, though relative male and female size is not definitively known.

The Deccan Plateau (/ˈdɛkən/ DEK-ən ) is a geographic formation that extends over an area of 422,000 km (163,000 sq mi) on the southern part of the Indian peninsula. It stretches from the Satpura and Vindhya Ranges in the north to the northern fringes of Tamil Nadu in the south. It is bound by the mountain ranges of the Western Ghats and the Eastern Ghats on the sides, which separate the region from the Western and Eastern Coastal Plains respectively. It covers most of the Indian States of Maharashtra, Karnataka, Telangana and Andhra Pradesh excluding the coastal regions, and minor portions of Tamil Nadu and Kerala.

The plateau is marked by rocky terrain with an average elevation of about 600 m (2,000 ft). It is subdivided into Maharashtra Plateau, Karnataka Plateau, and Rayalaseema and Telangana Plateau. The Deccan Traps in the northwest were formed by multiple layers of igneous rock deposited by basaltic lava flows following a massive volcanic eruption occurred at the end of the Cretaceous period (66 mya). The underlying bed consists of granite and sedimentary rocks formed during the Precambrian era and the formation of Gondwana.