The history of the Earth concerns the development of the planet Earth from its formation to the present day.Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's past. The age of Earth is approximately one-third of the age of the universe. An immense amount of biological and geological change has occurred in that time span.
Earth formed around 4.54 billion (4.54×109) years ago by accretion from the solar nebula. Volcanic outgassing likely created the primordial atmosphere, but it contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of extreme volcanism and frequent collisions with other bodies. One very large collision is thought to have been responsible for tilting the Earth at an angle and forming the Moon. Over time, the planet cooled and formed a solid crust, allowing liquid water to exist on the surface. The first life forms appeared between 3.8 and 3.5 billion years ago. Photosynthetic life appeared around 2 billion years ago, enriching the atmosphere with oxygen. Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose. During the Cambrian period it experienced a rapid diversification into most major phyla.
Biological and geological change has been constantly occurring on our planet since the time of its formation. Organisms continuously evolve, taking on new forms or going extinct in response to an ever-changing planet. The process of plate tectonics has played a major role in the shaping of Earth's oceans and continents, as well as the life they harbor. The biosphere, in turn, has had a significant effect on the atmosphere and other abiotic conditions on the planet, such as the formation of the ozone layer, the proliferation of oxygen, and the creation of soil.
The following four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this compresses the most recent eon. Therefore the second scale shows the most recent eon with an expanded scale. Finally, the second scale again compresses the most recent era, so the latest era is expanded in the third scale. Since the Quaternary is a very short period with short epochs, it is expanded in the fourth scale. The second, third, and fourth timelines are therefore each subsections of their preceding timeline as indicated by asterisks. The Holocene (the latest epoch) is too small to be shown clearly on the third timeline on the right, another reason for expanding the fourth scale. The Pleistocene (P) epoch. Q stands for the Quaternary period.
The center of the nebula, not having much angular momentum, collapsed rapidly, the compression heating it until nuclear fusion of hydrogen into helium began. After more contraction, a T Tauri star ignited and evolved into the Sun. Meanwhile, in the outer part of the nebula gravity caused matter to condense around density perturbations and dust particles, and the rest of the protoplanetary disk began separating into rings. In a process known as runaway accretion, successively larger fragments of dust and debris clumped together to form planets. Earth formed in this manner about 4.54 billion years ago (with an uncertainty of 1%)and was largely completed within 10–20 million years. The solar wind of the newly formed T Tauri star cleared out most of the material in the disk that had not already condensed into larger bodies. The same process is expected to produce accretion disks around virtually all newly forming stars in the universe, some of which yield planets.
The proto-Earth grew by accretion until its interior was hot enough to melt the heavy, siderophile metals. Having higher densities than the silicates, these metals sank. This so-called iron catastrophe resulted in the separation of a primitive mantle and a (metallic) core only 10 million years after the Earth began to form, producing the layered structure of Earth and setting up the formation of Earth's magnetic field. J. A. Jacobs was the first to suggest that the inner core—a solid center distinct from the liquid outer core is freezing and growing out of the liquid outer core due to the gradual cooling of Earth's interior (about 100 degrees Celsius per billion years). Extrapolations[citation needed] on these observations estimate that the inner core formed approximately 2-4 billion years ago, from what was previously an entirely molten core. If true, this would mean that the Earth's inner core is not a primordial feature inherited during the planet's formation, since it would be younger than the age of Earth (about 4.5 billion years). of which the atmosphere is now depleted in these elements compared to cosmic abundances.
The Mesozoic ("middle life") era lasted from 251 Ma to 66 Ma. It is subdivided into the Triassic, Jurassic, and Cretaceous periods. The era began with the Permian–Triassic extinction event, the most severe extinction event in the fossil record; 95% of the species on Earth died out. It ended with the Cretaceous–Paleogene extinction event that wiped out the dinosaurs. The Permian-Triassic 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[134] 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. Life persevered, and around 230 Ma, dinosaurs split off from their reptilian ancestors. The Triassic–Jurassic extinction event at 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 small animals resembling shrews.
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 angiosperms evolving flowers is during the Cretaceous period, some 20 million years later (132 Ma).66 Ma, a 10-kilometre (6.2 mi) asteroid 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, became extinct, marking the end of the Cretaceous period and Mesozoic era.
Mammals have existed since the late Triassic, but prior to the
Cretaceous–Paleogene extinction event they remained small. During the
Cenozoic, mammals rapidly diversified to fill some of the niches that
the dinosaurs and other extinct animals had left behind, branching out
into many of the modern orders. With many marine reptiles extinct, some
mammals began living in the oceans and became cetaceans. Others became felids and canids,
swift and agile land predators. The drier global climate of the
Cenozoic led to the expansion of grasslands and the evolution of grazing
and hoofed mammals such as equids and bovids. Some arboreal mammals became the primates, of which one lineage would lead to modern humans.
The ability to control fire probably began in Homo erectus (or Homo ergaster), probably at least 790,000 years ago but perhaps as early as 1.5 Ma. The use and discovery of controlled fire may even predate Homo erectus. 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 brain size increased, babies were born earlier, before their heads grew too large to pass through the pelvis. 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. Modern humans (Homo sapiens) are believed to have originated around 200,000 years ago or earlier in Africa; the oldest fossils date back to around 160,000 years ago.
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.However, evidence of more sophisticated beliefs, such as the early Cro-Magnon cave paintings (probably with magical or religious significance) did not appear until 32,000 years ago.Cro-Magnons also left behind stone figurines such as Venus of Willendorf, probably also signifying religious belief.By 11,000 years ago, Homo sapiens had reached the southern tip of South America, the last of the uninhabited continents (except for Antarctica, which remained undiscovered until 1820 AD). Tool use and communication continued to improve, and interpersonal relationships became more intricate.
Throughout more than 90% of its history, Homo sapiens lived in small bands as nomadic hunter-gatherers. As language became more complex, the ability to remember and communicate information resulted in a new replicator: the meme.Ideas could be exchanged quickly and passed down the generations. Cultural evolution quickly outpaced biological evolution, and history proper began. Between 8500 and 7000 BC, humans in the Fertile Crescent in Middle East began the systematic husbandry of plants and animals: agriculture. This spread to neighboring regions, and developed independently elsewhere, until most Homo sapiens
lived sedentary lives in permanent settlements as farmers. Not all
societies abandoned nomadism, especially those in isolated areas of the
globe poor in domesticable plant species, such as Australia.
However, among those civilizations that did adopt agriculture, the
relative stability and increased productivity provided by farming
allowed the population to expand.
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. This led to Earth’s first civilization at Sumer in the Middle East, between 4000 and 3000 BC. Additional civilizations quickly arose in ancient Egypt, at the Indus River valley and in China. 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—curiosity and education drove the pursuit of knowledge and wisdom.
Various disciplines, including science (in a primitive form), arose. New civilizations sprang up, traded with one another, and fought for territory and resources. Empires soon began to develop. By around 500 BC, there were advanced civilizations in the Middle East, Iran, India, China, and Greece, at times expanding, at times entering into decline. In 221 BC, China became a single polity that would grow to spread its culture throughout eastern Asia, and it has remained the most populous nation in the world. The fundamentals of the Western world were largely shaped by the ancient Greco-Roman culture. The Roman Empire was Christianized by Emperor Constantine in the early fourth century and declined by the end of the fifth. Beginning with the seventh century, Christianization of Europe began. In 610, Islam was founded and quickly became the dominant religion in western Asia. In 1054 CE the Great Schism between the Roman Catholic Church and the Eastern Orthodox Church led to the prominent cultural differences between Western and Eastern Europe.
In the fourteenth century, the Renaissance began in Italy with advances in religion, art, and science. At that time the Christian Church as a political entity lost much of its power. In 1492, Christopher Columbus reached the Americas, initiating great changes to the new world. European civilization began to change beginning in 1500, leading to the scientific and industrial revolutions. That continent began to exert political and cultural dominance over human societies around the planet, a time known as the Colonial era (also see Age of Discovery).In the eighteenth century a cultural movement known as the Age of Enlightenment further shaped the mentality of Europe and contributed to its secularization. From 1914 to 1918 and 1939 to 1945, 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 failing to prevent World War II, mankind's bloodiest conflict, it was replaced by the United Nations. 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 1992, 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 mid-1940s 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 1957, 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 Voyager) having left the solar system. The Soviet Union and the United States were the earliest leaders in space exploration in the 20th century. 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 2000. The World Wide Web was developed in the 1990s and since then has proved to be an indispensable source of information in the developed world.
Earth formed around 4.54 billion (4.54×109) years ago by accretion from the solar nebula. Volcanic outgassing likely created the primordial atmosphere, but it contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of extreme volcanism and frequent collisions with other bodies. One very large collision is thought to have been responsible for tilting the Earth at an angle and forming the Moon. Over time, the planet cooled and formed a solid crust, allowing liquid water to exist on the surface. The first life forms appeared between 3.8 and 3.5 billion years ago. Photosynthetic life appeared around 2 billion years ago, enriching the atmosphere with oxygen. Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose. During the Cambrian period it experienced a rapid diversification into most major phyla.
Biological and geological change has been constantly occurring on our planet since the time of its formation. Organisms continuously evolve, taking on new forms or going extinct in response to an ever-changing planet. The process of plate tectonics has played a major role in the shaping of Earth's oceans and continents, as well as the life they harbor. The biosphere, in turn, has had a significant effect on the atmosphere and other abiotic conditions on the planet, such as the formation of the ozone layer, the proliferation of oxygen, and the creation of soil.
Geological time, condensed in a diagram displaying the relative lengths of the eons of Earth's history
Geologic time scale
The history of the Earth is organized chronologically in a table known as the geologic time scale, which is split into intervals based on stratigraphic analysis.A full-time scale can be found at the main article.The following four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this compresses the most recent eon. Therefore the second scale shows the most recent eon with an expanded scale. Finally, the second scale again compresses the most recent era, so the latest era is expanded in the third scale. Since the Quaternary is a very short period with short epochs, it is expanded in the fourth scale. The second, third, and fourth timelines are therefore each subsections of their preceding timeline as indicated by asterisks. The Holocene (the latest epoch) is too small to be shown clearly on the third timeline on the right, another reason for expanding the fourth scale. The Pleistocene (P) epoch. Q stands for the Quaternary period.
Solar System formation
The standard model for the formation of the Solar System (including the Earth) is the solar nebula hypothesis. In this model, the Solar system formed from a large, rotating cloud of interstellar dust and gas called the solar nebula. It was composed of hydrogen and helium created shortly after the Big Bang 13.8 Ga (billion years ago) and heavier elements ejected by supernovae. About 4.5 Ga, the nebula began a contraction that may have been triggered by the shock wave of a nearby supernova.A shock wave would have also made the nebula rotate. As the cloud began to accelerate, its angular momentum, gravity and inertia flattened it into a protoplanetary disk perpendicular to its axis of rotation. Small perturbations due to collisions and the angular momentum of other large debris created the means by which kilometer-sized protoplanets began to form, orbiting the nebular center.The center of the nebula, not having much angular momentum, collapsed rapidly, the compression heating it until nuclear fusion of hydrogen into helium began. After more contraction, a T Tauri star ignited and evolved into the Sun. Meanwhile, in the outer part of the nebula gravity caused matter to condense around density perturbations and dust particles, and the rest of the protoplanetary disk began separating into rings. In a process known as runaway accretion, successively larger fragments of dust and debris clumped together to form planets. Earth formed in this manner about 4.54 billion years ago (with an uncertainty of 1%)and was largely completed within 10–20 million years. The solar wind of the newly formed T Tauri star cleared out most of the material in the disk that had not already condensed into larger bodies. The same process is expected to produce accretion disks around virtually all newly forming stars in the universe, some of which yield planets.
The proto-Earth grew by accretion until its interior was hot enough to melt the heavy, siderophile metals. Having higher densities than the silicates, these metals sank. This so-called iron catastrophe resulted in the separation of a primitive mantle and a (metallic) core only 10 million years after the Earth began to form, producing the layered structure of Earth and setting up the formation of Earth's magnetic field. J. A. Jacobs was the first to suggest that the inner core—a solid center distinct from the liquid outer core is freezing and growing out of the liquid outer core due to the gradual cooling of Earth's interior (about 100 degrees Celsius per billion years). Extrapolations[citation needed] on these observations estimate that the inner core formed approximately 2-4 billion years ago, from what was previously an entirely molten core. If true, this would mean that the Earth's inner core is not a primordial feature inherited during the planet's formation, since it would be younger than the age of Earth (about 4.5 billion years). of which the atmosphere is now depleted in these elements compared to cosmic abundances.
Hadean and Archean Eons
The first eon in Earth's history, the Hadean, begins with the Earth's formation and is followed by the Archean eon at 3.8 Ga.The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga, soon after the formation of the Earth's crust and the Earth itself. The giant impact hypothesis for the Moon's formation states that shortly after formation of an initial crust, the proto-Earth was impacted by a smaller protoplanet, which ejected part of the mantle and crust into space and created the Moon.
From crater counts on other celestial bodies it is inferred that a period of intense meteorite impacts, called the Late Heavy Bombardment, began about 4.1 Ga, and concluded around 3.8 Ga, at the end of the Hadean. In addition, volcanism was severe due to the large heat flow and geothermal gradient., detrital zircon crystals dated to 4.4 Ga show evidence of
having undergone contact with liquid water, suggesting that the planet
already had oceans or seas at that time.
By the beginning of the Archean, the Earth had cooled significantly.
Most present life forms could not have survived in the Archean
atmosphere, which lacked oxygen and an ozone layer. Nevertheless it is believed that primordial life began to evolve by the early Archean, with candidate fossils dated to around 3.5 Ga.
Some scientists even speculate that life could have begun during the
early Hadean, as far back as 4.4 Ga, surviving the possible Late Heavy
Bombardment period in hydrothermal vents below the Earth's surface.
Mesozoic Era
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 angiosperms evolving flowers is during the Cretaceous period, some 20 million years later (132 Ma).66 Ma, a 10-kilometre (6.2 mi) asteroid 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, became extinct, marking the end of the Cretaceous period and Mesozoic era.
Cenozoic Era
The Cenozoic era began at 66 Ma,and is subdivided into the Paleogene, Neogene, and Quaternary periods. Mammals and birds were able to survive the Cretaceous–Paleogene extinction event which killed off the dinosaurs and many other forms of life, and this is the era in which they diversified into their modern forms.Diversification of mammals
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Human evolution
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 brain size increased, babies were born earlier, before their heads grew too large to pass through the pelvis. 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. Modern humans (Homo sapiens) are believed to have originated around 200,000 years ago or earlier in Africa; the oldest fossils date back to around 160,000 years ago.
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.However, evidence of more sophisticated beliefs, such as the early Cro-Magnon cave paintings (probably with magical or religious significance) did not appear until 32,000 years ago.Cro-Magnons also left behind stone figurines such as Venus of Willendorf, probably also signifying religious belief.By 11,000 years ago, Homo sapiens had reached the southern tip of South America, the last of the uninhabited continents (except for Antarctica, which remained undiscovered until 1820 AD). Tool use and communication continued to improve, and interpersonal relationships became more intricate.
Civilization
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. This led to Earth’s first civilization at Sumer in the Middle East, between 4000 and 3000 BC. Additional civilizations quickly arose in ancient Egypt, at the Indus River valley and in China. 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—curiosity and education drove the pursuit of knowledge and wisdom.
Various disciplines, including science (in a primitive form), arose. New civilizations sprang up, traded with one another, and fought for territory and resources. Empires soon began to develop. By around 500 BC, there were advanced civilizations in the Middle East, Iran, India, China, and Greece, at times expanding, at times entering into decline. In 221 BC, China became a single polity that would grow to spread its culture throughout eastern Asia, and it has remained the most populous nation in the world. The fundamentals of the Western world were largely shaped by the ancient Greco-Roman culture. The Roman Empire was Christianized by Emperor Constantine in the early fourth century and declined by the end of the fifth. Beginning with the seventh century, Christianization of Europe began. In 610, Islam was founded and quickly became the dominant religion in western Asia. In 1054 CE the Great Schism between the Roman Catholic Church and the Eastern Orthodox Church led to the prominent cultural differences between Western and Eastern Europe.
In the fourteenth century, the Renaissance began in Italy with advances in religion, art, and science. At that time the Christian Church as a political entity lost much of its power. In 1492, Christopher Columbus reached the Americas, initiating great changes to the new world. European civilization began to change beginning in 1500, leading to the scientific and industrial revolutions. That continent began to exert political and cultural dominance over human societies around the planet, a time known as the Colonial era (also see Age of Discovery).In the eighteenth century a cultural movement known as the Age of Enlightenment further shaped the mentality of Europe and contributed to its secularization. From 1914 to 1918 and 1939 to 1945, 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 failing to prevent World War II, mankind's bloodiest conflict, it was replaced by the United Nations. 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 1992, 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.
Recent events
In 1957, 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 Voyager) having left the solar system. The Soviet Union and the United States were the earliest leaders in space exploration in the 20th century. 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 2000. The World Wide Web was developed in the 1990s and since then has proved to be an indispensable source of information in the developed world.
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