The process may have finally been reversed by the emission of carbon dioxide from volcanoes or the destabilization of methane gas hydrates. According to the alternative Slushball Earth theory, even at the height of the ice ages there was still open water at the Equator. Modern taxonomy classifies life into three domains. The time of their origin is uncertain. The Bacteria domain probably first split off from the other forms of life sometimes called Neomura , but this supposition is controversial.
Soon after this, by 2 Ga,  the Neomura split into the Archaea and the Eukarya. Eukaryotic cells Eukarya are larger and more complex than prokaryotic cells Bacteria and Archaea , and the origin of that complexity is only now becoming known. Around this time, the first proto-mitochondrion was formed. A bacterial cell related to today's Rickettsia ,  which had evolved to metabolize oxygen , entered a larger prokaryotic cell, which lacked that capability. Perhaps the large cell attempted to digest the smaller one but failed possibly due to the evolution of prey defenses.
The smaller cell may have tried to parasitize the larger one. In any case, the smaller cell survived inside the larger cell. Using oxygen, it metabolized the larger cell's waste products and derived more energy. Part of this excess energy was returned to the host. The smaller cell replicated inside the larger one. Soon, a stable symbiosis developed between the large cell and the smaller cells inside it. Over time, the host cell acquired some genes from the smaller cells, and the two kinds became dependent on each other: the larger cell could not survive without the energy produced by the smaller ones, and these, in turn, could not survive without the raw materials provided by the larger cell.
The whole cell is now considered a single organism , and the smaller cells are classified as organelles called mitochondria. A similar event occurred with photosynthetic cyanobacteria  entering large heterotrophic cells and becoming chloroplasts. There were probably several such inclusion events. Besides the well-established endosymbiotic theory of the cellular origin of mitochondria and chloroplasts, there are theories that cells led to peroxisomes , spirochetes led to cilia and flagella , and that perhaps a DNA virus led to the cell nucleus,   though none of them are widely accepted.
Archaeans, bacteria, and eukaryotes continued to diversify and to become more complex and better adapted to their environments. Each domain repeatedly split into multiple lineages, although little is known about the history of the archaea and bacteria. Around 1. Some of these lived in colonies, and gradually a division of labor began to take place; for instance, cells on the periphery might have started to assume different roles from those in the interior. At first, it probably resembled today's sponges , which have totipotent cells that allow a disrupted organism to reassemble itself.
No ocean crust dates back further than that, so earlier reconstructions are more difficult. Paleomagnetic poles are supplemented by geologic evidence such as orogenic belts , which mark the edges of ancient plates, and past distributions of flora and fauna. The further back in time, the scarcer and harder to interpret the data get and the more uncertain the reconstructions. Throughout the history of the Earth, there have been times when continents collided and formed a supercontinent, which later broke up into new continents.
The hypothetical supercontinent is sometimes referred to as Pannotia or Vendia. The existence of Pannotia depends on the timing of the rifting between Gondwana which included most of the landmass now in the Southern Hemisphere, as well as the Arabian Peninsula and the Indian subcontinent and Laurentia roughly equivalent to current-day North America. The end of the Proterozoic saw at least two Snowball Earths, so severe that the surface of the oceans may have been completely frozen.
Palomar College. Gerald D. Stars with more "metals" — a term astronomers use for elements other than hydrogen and helium — in their cores have more giant planets than their metal-poor cousins. UCMP Glossary. We know the quantities of sand in both containers at the start. The continents of Ur , Vaalbara and Kenorland may have existed around this time.
This happened about Because CO 2 is an important greenhouse gas, climates cooled globally. An alternative hypothesis is that enough carbon dioxide escaped through volcanic outgassing that the resulting greenhouse effect raised global temperatures. The Cryogenian period was followed by the Ediacaran period, which was characterized by a rapid development of new multicellular lifeforms.
The new forms of life, called Ediacara biota, were larger and more diverse than ever. Though the taxonomy of most Ediacaran life forms is unclear, some were ancestors of groups of modern life. None of the Ediacaran fossils had hard body parts like skeletons. These first appear after the boundary between the Proterozoic and Phanerozoic eons or Ediacaran and Cambrian periods.
The Phanerozoic is the current eon on Earth, which started approximately million years ago. It consists of three eras: The Paleozoic , Mesozoic , and Cenozoic ,  and is the time when multi-cellular life greatly diversified into almost all the organisms known today. Life colonized the land, first plants, then animals.
Two major extinctions occurred. The continents formed at the break-up of Pannotia and Rodinia at the end of the Proterozoic slowly moved together again, forming the supercontinent Pangaea in the late Paleozoic. These three periods are further split into seven sub-divisions, with the Paleogene composed of The Paleocene , Eocene , and Oligocene , the Neogene divided into the Miocene , Pliocene , and the Quaternary composed of the Pleistocene , and Holocene. At the end of the Proterozoic, the supercontinent Pannotia had broken apart into the smaller continents Laurentia, Baltica , Siberia and Gondwana.
Because young volcanic crust is relatively hotter and less dense than old oceanic crust, the ocean floors rise during such periods. This causes the sea level to rise. Therefore, in the first half of the Paleozoic, large areas of the continents were below sea level. Early Paleozoic climates were warmer than today, but the end of the Ordovician saw a short ice age during which glaciers covered the south pole, where the huge continent Gondwana was situated. Traces of glaciation from this period are only found on former Gondwana. During the Late Ordovician ice age, a few mass extinctions took place, in which many brachiopods , trilobites, Bryozoa and corals disappeared.
These marine species could probably not contend with the decreasing temperature of the sea water. The biological fomenting in the Cambrian Explosion was unpreceded before and since that time. The development of hard body parts such as shells, skeletons or exoskeletons in animals like molluscs , echinoderms , crinoids and arthropods a well-known group of arthropods from the lower Paleozoic are the trilobites made the preservation and fossilization of such life forms easier than those of their Proterozoic ancestors.
For this reason, much more is known about life in and after the Cambrian than about that of older periods. Some of these Cambrian groups appear complex but are seemingly quite different from modern life; examples are Anomalocaris and Haikouichthys. More recently, however, these seem to have found a place in modern classification. During the Cambrian, the first vertebrate animals, among them the first fishes , had appeared. It had a primitive notochord , a structure that could have developed into a vertebral column later.
The first fishes with jaws Gnathostomata appeared during the next geological period, the Ordovician. The colonisation of new niches resulted in massive body sizes. The diversity of life forms did not increase greatly because of a series of mass extinctions that define widespread biostratigraphic units called biomeres.
Oxygen accumulation from photosynthesis resulted in the formation of an ozone layer that absorbed much of the 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. Prokaryote lineages  had probably colonized the land as early as 2. For a long time, the land remained barren of multicellular organisms.
Several hundred million years ago, plants probably resembling algae and fungi started growing at the edges of the water, and then out of it. There is also unconfirmed evidence that arthropods may have appeared on land as early as Ma. This would let them live in oxygen-poor water, or pursue small prey in shallow water.
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 amphibians. This resulted in the divergence of amniotes from amphibians. Other groups of organisms continued to evolve, and lines diverged—in fish, insects, bacteria, and so on—but less is known of the details. Though some mammalian lines began to separate during this period, existing mammals were probably small animals resembling shrews.
The first of five great mass extinctions was the Ordovician-Silurian extinction. Its possible cause was the intense glaciation of Gondwana, which eventually led to a snowball earth. The second mass extinction was the Late Devonian extinction , probably caused by the evolution of trees, which could have led to the depletion of greenhouse gases like CO2 or the eutrophication of water.
The third mass extinction was the Permian-Triassic, or the Great Dying , event was possibly caused by some combination of the Siberian Traps volcanic event, an asteroid impact, methane hydrate gasification, sea level fluctuations, and a major anoxic event. Either the proposed Wilkes Land crater  in Antarctica or Bedout structure off the northwest coast of Australia may indicate an impact connection with the Permian-Triassic extinction.
But it remains uncertain whether either these or other proposed Permian-Triassic boundary craters are either real impact craters or even contemporaneous with the Permian-Triassic extinction event. The fourth mass extinction was the Triassic-Jurassic extinction event in which almost all synapsids and archosaurs became extinct, probably due to new competition from dinosaurs.
The fifth and most recent mass extinction was the K-T extinction. This ejected vast quantities of particulate matter and vapor into the air that occluded sunlight, inhibiting photosynthesis. The first true mammals evolved in the shadows of dinosaurs and other large archosaurs that filled the world by the late Triassic.
The first mammals were very small, and were probably nocturnal to escape predation. Mammal diversification truly began only after the Cretaceous-Paleogene extinction event. Creatures like Ambulocetus took to the oceans to eventually evolve into whales,  whereas some creatures, like primates, took to the trees. Grassless savannas began to predominate much of the landscape, and mammals such as Andrewsarchus rose up to become the largest known terrestrial predatory mammal ever,  and early whales like Basilosaurus took control of the seas.
The evolution of grass brought a remarkable change to the Earth's landscape, and the new open spaces created pushed mammals to get bigger and bigger. Grass started to expand in the Miocene, and the Miocene is where many modern- day mammals first appeared. Giant ungulates like Paraceratherium and Deinotherium evolved to rule the grasslands.
Despite the wealth of worlds in our own solar system, scientists still aren't certain how planets are built. The first and most widely accepted theory, core accretion, works well with the formation of the terrestrial planets like Earth but has problems with giant planets. The history of Earth concerns the development of planet Earth from its formation to the present Earth formed around billion years ago, approximately one- third the age of the universe, by accretion from the solar nebula. Volcanic.
The evolution of grass also brought primates down from the trees, and started human evolution. The first big cats evolved during this time as well. The formation of Panama was perhaps the most important geological event to occur in the last 60 million years. Atlantic and Pacific currents were closed off from each other, which caused the formation of the Gulf Stream , which made Europe warmer. The land bridge allowed the isolated creatures of South America to migrate over to North America, and vice versa. Three million years ago saw the start of the Pleistocene epoch, which featured dramatic climactic changes due to the ice ages.
The ice ages led to the evolution of modern man in Saharan Africa and expansion. The mega-fauna that dominated fed on grasslands that, by now, had taken over much of the subtropical world. The large amounts of water held in the ice allowed for various bodies of water to shrink and sometimes disappear such as the North Sea and the Bering Strait. It is believed by many that a huge migration took place along Beringia which is why, today, there are camels which evolved and became extinct in North America , horses which evolved and became extinct in North America , and Native Americans.
The ending of the last ice age coincided with the expansion of man, along with a massive die out of ice age mega-fauna. This extinction is nicknamed " the Sixth Extinction ".
Very soon after the split, for reasons that are still unclear, apes in one branch developed the ability to walk upright. Around the same time, the other branch split into the ancestors of the common chimpanzee and the ancestors of the bonobo as evolution continued simultaneously in all life forms. Fire was possibly used by the early Lower Paleolithic Oldowan hominid Homo habilis or strong australopithecines such as Paranthropus. It is more difficult to establish the origin of language ; it is unclear whether Homo erectus could speak or if that capability had not begun until Homo sapiens.
As a result, they exhibited more plasticity , and thus possessed an increased capacity to learn and required a longer period of dependence. Social skills became more complex, language became more sophisticated, and tools became more elaborate. This contributed to further cooperation and intellectual development. The first humans to show signs of spirituality are the Neanderthals usually classified as a separate species with no surviving descendants ; they buried their dead, often with no sign of food or tools.
Cultural evolution quickly outpaced biological evolution , and history proper began. Between and BC , humans in the Fertile Crescent in the Middle East began the systematic husbandry of plants and animals: agriculture. Not all societies abandoned nomadism, especially those in isolated areas of the globe poor in domesticable plant species, such as Australia. Agriculture had a major impact; humans began to affect the environment as never before. Surplus food allowed a priestly or governing class to arise, followed by increasing division of labor.
The invention of writing enabled complex societies to arise: record-keeping and libraries served as a storehouse of knowledge and increased the cultural transmission of information. Humans no longer had to spend all their time working for survival, enabling the first specialized occupations e. Curiosity and education drove the pursuit of knowledge and wisdom, and various disciplines, including science in a primitive form , arose. This in turn led to the emergence of increasingly larger and more complex civilizations, such as the first empires, which at times traded with one another, or fought for territory and resources.
By around BC, there were advanced civilizations in the Middle East, Iran, India, China, and Greece, at times expanding, at times entering into decline. The fundamentals of Western civilization were largely shaped in Ancient Greece , with the world's first democratic government and major advances in philosophy, science, and mathematics, and in Ancient Rome in law, government, and engineering.
Beginning with the 7th century, Christianization of Europe began. In , Islam was founded and quickly became the dominant religion in Western Asia. In the 14th century, the Renaissance began in Italy with advances in religion, art, and science. In , Christopher Columbus reached the Americas, initiating great changes to the new world. European civilization began to change beginning in , leading to the scientific and industrial revolutions. That continent began to exert political and cultural dominance over human societies around the world, a time known as the Colonial era also see Age of Discovery.
From to and to , nations around the world were embroiled in world wars.
Established following World War I , the League of Nations was a first step in establishing international institutions to settle disputes peacefully. After the war, many new states were formed, declaring or being granted independence in a period of decolonization. The United States and Soviet Union became the world's dominant superpowers for a time, and they held an often-violent rivalry known as the Cold War until the dissolution of the latter.
In , several European nations joined in the European Union. As transportation and communication improved, the economies and political affairs of nations around the world have become increasingly intertwined. This globalization has often produced both conflict and cooperation. Change has continued at a rapid pace from the mids to today. Technological developments include nuclear weapons , computers , genetic engineering , and nanotechnology.
Economic globalization , spurred by advances in communication and transportation technology, has influenced everyday life in many parts of the world. Cultural and institutional forms such as democracy , capitalism , and environmentalism have increased influence. Major concerns and problems such as disease , war , poverty , violent radicalism , and recently, human-caused climate change have risen as the world population increases.
In , the Soviet Union launched the first artificial satellite into orbit and, soon afterward, Yuri Gagarin became the first human in space. Neil Armstrong , an American, was the first to set foot on another astronomical object, the Moon.
Unmanned probes have been sent to all the known planets in the Solar System, with some such as the two Voyager spacecrafts having left the Solar System. Five space agencies, representing over fifteen countries,  have worked together to build the International Space Station. Aboard it, there has been a continuous human presence in space since From Wikipedia, the free encyclopedia.
This article is about scientific evidence concerning the history of Earth. For the history of humans, see History of the world. The development of planet Earth from its formation to the present day. Main article: Geologic time scale. Main article: Formation and evolution of the Solar System. See also: Planetary differentiation. Main articles: Hadean and Archean. Main articles: Moon , Origin of the Moon , and Giant impact hypothesis.
See also: Origin of the world's oceans. Life timeline. This box: view talk edit. Single-celled life. Multicellular life. Earliest water. Earliest life. Earliest oxygen. Atmospheric oxygen.
Oxygen crisis. Sexual reproduction. Earliest plants. Ediacara biota. Cambrian explosion. Earliest apes.
Axis scale : million years. See also: Human timeline , and Nature timeline. Main articles: Abiogenesis , Earliest known life forms , Evolution , and Evolutionary history of life. Main article: RNA world. Main article: iron—sulfur world theory.
Main article: Last universal ancestor. Main article: Proterozoic. Main article: Great Oxygenation Event. See also: Ozone layer. Main article: Snowball Earth. Main article: Supercontinent cycle. Main article: Phanerozoic. Main article: Cambrian explosion. Further information: Evolution of tetrapods. Further information: Evolution of mammals. Hominin timeline. Homo habilis. Homo erectus. Homo sapiens. Earlier apes. Gorilla split. Possibly bipedal. Chimpanzee split. Earliest bipedal. Stone tools. Exit from Africa. Earliest fire use. Earliest cooking. Earliest clothes. Modern speech.
See also: Life timeline , and Nature timeline. Main article: Human evolution. Main articles: History of the world and Cradle of civilization. Main article: Modern history. See also: Modernity and Future. Geological Survey. Archived from the original on 23 December Retrieved Brent Special Publications, Geological Society of London. Earth and Planetary Science Letters. William ; Kudryavtsev, Anatoliy B. Precambrian Research. This model showed that after the collision, the magma on Earth would have been heated far more than solids from the impacting object. This would cause the magma to expand in volume and escape into orbit to form the Moon.
This latest model, which takes into account the different degree of heating between the proto-Earth and Theia, effectively explains how there is much more Earth material in the makeup of the Moon. Shun-ichiro Karato, a professor of geology at Yale University and a co-author on the paper, has conducted extensive research on the chemical properties of proto-Earth magma in the past.
As he explained in an interview with Yale News :. This is a big difference. Taken together, the new model demonstrated that superheated magma would be lost to space and coalesce to form a new body in orbit faster than the material lost from the impactor. Essentially, the new model confirms previous theories about how the Moon formed by doing away with the need for unconventional collision conditions.
Dasgupta said it does not appear that Earth's bulk silicate, on its own, could have attained the life-essential volatile budgets that produced our biosphere, atmosphere and hydrosphere. Materials provided by Rice University. Note: Content may be edited for style and length. Science News. Story Source: Materials provided by Rice University. Journal Reference : Damanveer S. Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact. ScienceDaily, 23 January Rice University.
Planetary collision that formed the moon made life possible on Earth: Study: Planetary delivery explains enigmatic features of Earth's carbon and nitrogen. Retrieved June 26, from www.