Earth, also called the world and, less frequently, Terra (especially in science fiction) or Gaia, is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to accommodate life. Earth's biodiversity has evolved over hundreds of millions of years, expanding continually except when interrupted by mass extinctions. Although scholars estimate that over 99 percent of all species that ever lived on the planet are extinct, Earth is currently home to 10–14 million species of life,including over 7.2 billion humans,who depend upon its biosphere and minerals. Earth's human population is divided among about two hundred sovereign states which interact through diplomacy, conflict, travel, trade, and communication media.
According to evidence from radiometric dating and other sources, Earth was formed around four and a half billion years ago. Within its first billion years,life appeared in its oceans and began to affect its atmosphere and surface, promoting the proliferation of aerobic as well as anaerobic organisms and causing the formation of the atmosphere's ozone layer. This layer and the geomagnetic field block the most life-threatening parts of the Sun's radiation, so life was able to flourish on land as well as in water. Since then, the combination of Earth's distance from the Sun, its physical properties, and its geological history have allowed life to persist.
Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. Seventy-one percent of Earth's surface is covered with water, with the remainder consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with ice that includes the solid ice of the Antarctic ice sheet and the sea ice of the polar ice packs. Earth's interior remains active, with a solid iron inner core, a liquid outer core that generates the magnetic field, and a thick layer of relatively solid mantle.
Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, Earth rotates about its own axis 366.26 times, creating 365.26 solar days, or one sidereal year. Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). The Moon is Earth's only natural satellite. It began orbiting Earth about 4.53 billion years ago . The Moon's gravitational interaction with Earth stimulates ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation.
Scientists Find Evidence For Oceans Of Water Far Below Earth’s Crust:
A group of researchers have discovered evidence for oceans' worth of water deep beneath the country which, according to them, could represent the largest water reservoir on Earth.
The researchers have found the ingredients for water in rocks deep in the Earth’s mantle nearly 400 miles beneath North America, suggesting that water, driven from the Earth’s surface by plate tectonics, could be there at such depths. The findings, published in the journal Science on Friday, are expected to help scientists better understand the Earth’s formation and its current composition, and to reveal the amount of water buried deep below.
“Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight,” Steve Jacobsen, a geophysicist at the Northwestern University in Illinois and the study’s co-author, said in a statement. “I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”
According to Jacobsen and the University of New Mexico seismologist Brandon Schmandt, they have “direct evidence” that a rocky layer of the Earth’s mantle -- known as “transition zone” -- located at depths between 250 miles and 410 miles has water trapped in it on a regional scale, extending across most of the interior of the country.
As part of the study, Schmandt observed seismic data from earthquakes to investigate the structure of the Earth’s deep crust and mantle while Jacobsen used those observations in the laboratory to study mantle rock under the simulated high pressures of 400 miles below the Earth’s surface.
Earth interior water:
Schematic cross section of the Earth’s interior. Northwestern University
“Melting of rock at this depth is remarkable because most melting in the mantle occurs much shallower, in the upper 50 miles,” Schmandt said in the statement. “If there is a substantial amount of H2O in the transition zone, then some melting should take place in areas where there is flow into the lower mantle, and that is consistent with what we found.”
According to the researchers, if water accounts for only 1 percent of the weight of mantle rock located in the transition zone, it would be equivalent to nearly three times the amount of water in Earth’s oceans.
However, the scientists said that the water in such great depths is not found in the form of liquid, ice or vapor. Rather, it is a form of water that is trapped inside the molecular structure of the minerals in the mantle rock.
“The weight of 250 miles of solid rock creates such high pressure, along with temperatures above 2,000 degrees Fahrenheit, that a water molecule splits to form a hydroxyl radical (OH), which can be bound into a mineral’s crystal structure,” the scientists said.
Water Discovered Deep Under Earth's Surface:
Scientists just found a new ocean, and it’s not where you think. According to a new study, a huge amount of water is trapped beneath Earth’s surface enough to fill several oceans. At 440 miles beneath the planet’s surface, the water isn’t accessible for use right any time soon, but it does give clues as to where all our water came from and where we can go from here.
The water isn’t exactly usable in its present state. According to the authors of the study, it’s trapped within a layer of a crystalline mineral called ringwoodite, which acts like an extremely hard, subterranean sponge. Because of the way it’s trapped, the water isn’t even liquid (or ice or vapor), instead taking the form of hydroxide ions containing both hydrogen and oxygen. If it were liquid, though, the researchers say that the pockets of ions could fill the world’s oceans.
There’s one big catch: the size of the ringwoodite layer beneath the planet’s surface has yet to be confirmed. But the scientists did use a network of over 2,000 seismometers around the United States to make a map of Earth’s internal structure. They found that material flowing downward melts as it passes through the 400-mile-deep “transition zone” of the planet’s insides. ”If we are seeing this melting, then there has to be this water in the transition zone,” said the University of New Mexico’s Brandon Schmandt, a coauthor of the study. “The transition zone can hold a lot of water, and could potentially have the same amount of H2O as all the world’s oceans.”
The scientists believe their findings are evidence that the water on Earth’s surface originally came from somewhere underground and that the water cycle extends much deeper than many people thought, perhaps even contributing to the stability of oceans today. ”The surface water we have now came from degassing of molten rock. It came from the original rock ingredients of Earth,” Schmandt said. “How much water is still inside the Earth today relative to the surface?”
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