internal heat of earth.

Jul 4, 2021
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Can anybody tell me, that how long will the internal heat of earth continue. Will it gradually cool down? or stay producing the heat continuously? Moreover, where is this heat coming from? What is the source/ reason behind this heat?
 
Jan 27, 2020
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akramjanjaffar, there is a race going on between a cooling Earth and the death of our sun.

The earth is stratified into layers by density (heavy core, intermediate mantle, light lithosphere), telling us that early in its history the earth went through a molten stage that led to the heavy materials sinking inward to form the core, and the lighter materials floating toward the surface like a slag to form the crust. The heat for this melting came from meteorite impacts, the planetary caroming of the Earth which created the moon, and the decay of radioactive elements.

Earth-crust-cutaway-numbered.svg.png
Gringer, Washiucho - File:Earth-crust-cutaway-japanese.svg
Earth and atmosphere cutaway illustration 1: Crust 2: Moho 3: Upper Mantle 4: Low-velocity Zone 5: Lower Mantle 6: D"–Layer 7: Outer Core 8: Liquid–Solid Boundary 9: Inner Core A: Troposphere B: Stratosphere C: Mesophere D: Thermosphere E: Exosphere


Had we flown by the earth in a space ship about 4.3 billion years ago; all we would have seen was a glowing red hot ball of seething magma being pelted by meteorites of all sizes.

All of the geological activity on the earth today is driven from this initial source of heat at the Earth's formation, abetted by continued radioactive decay of elements in the Earth's interior. And it’s producing almost as much heat as it’s losing. The process by which Earth makes heat is called radioactive decay. It involves the disintegration of natural radioactive elements inside the Earth – Uranium-238, Uranium-235, Thorium-232, and Potassium-40, all of which have half-lives of greater than 700 million years (up to about 14 billion years for Thorium). Uranium is a special kind of element because when it decays, a lot of heat is produced. It’s this heat that keeps Earth from cooling off completely.

Our estimates for the melting temperature of iron at these conditions in the Earth's outer core range from about 4,500 to 7,500 kelvins (about 7,600 to 13,000 degrees F). As the outer core is fluid and presumably convecting (and with an additional correction for the presence of impurities in the outer core), we can extrapolate this range of temperatures to a temperature at the base of Earth's mantle (the top of the outer core) of roughly 3,500 to 5,500 kelvins (5,800 to 9,400 degrees F) at the base of the earth's mantle.

While the heat energy produced inside Earth is enormous, it’s some 5,000 times less powerful than what Earth receives from the sun. The sun’s heat drives the weather and ultimately causes erosion. So it’s ironic that – while Earth’s heat makes mountains through subduction – the sun’s energy makes the weather which tears them down again, bit by bit, over time.
(See: the Wilson cycle: http://csmgeo.csm.jmu.edu/geollab/Fichter/Wilson/wilsonsimp.html)

The Earth's heat engine ran faster at the beginning than now, about three times faster. Considering how active the Earth is now with earthquakes and volcanoes, it must have been incredible four billion years ago to have it running even faster. But the Earth is cooling off, and as time goes by there will be less and less heat to escape, as the internal radioactive material decreases, until there is no heat left at all.

Four billion years ago the our planet had cooled enough for the outer layers to solidify and for oceans to form. Flying past the Earth at this time we would see a vast ocean, thanks to the water delivered from comets and meteors, from pole to pole, with volcanoes scattered here and there but no continents. The oldest rocks we have date to 3.96 billion years ago, and contain evidence of sedimentary rocks that require water.

Our planet cooled from the outside in, and the still molten iron-nickle core are the remnants of that heat from the early stage of melting. That heat is also what keeps the earth geologically active, and without it nothing that we know of the earth would exist today, no continents, no volcanos, no mountains, no oceans, and almost certainly no life - we would have a dead planet like Mars or Old Mr Moon, our romantic friend in the night sky.

Our planet is losing its heat through its convection cells in the mantle. That is how hot, low density material from the lower mantle, heated by the core, flows upward towards the surface where the heat escapes through volcanic activity and ocean vents. The cooled, now denser material then sinks back toward the core to be heated again. This creates a cycle of movement, but it is very slow, taking on the order of a billion years of so for a complete cycle.

convection cells.jpg
sciencestruck.com

Many convection cells exist simultaneously all over the planet, and they lead to widely scattered volcanic activity, like the Pacific Ocean's Ring of Fire*, ocean vents** and plate tectonic*** processes.

The time involved for a planet the size of the Earth to cool by convection, when the Earth has been geologically active for over 4 billion years, is another 4-5 billion years to loose all its heat -and become a dead planet.

By this latter time, however, the sun will have expanded into its red giant phase and burned the earth to a cinder before that final heat death of the core overcomes us.

red giant.jpg

sun to red giant.jpg
epoch times.se

See: https://www.scientificamerican.com/article/why-is-the-earths-core-so/

See: https://earthsky.org/earth/what-is-the-source-of-the-heat-in-the-earths-interior/

See: https://earthscience.stackexchange.com/questions/428/could-the-earths-core-lose-its-heat

See: http://csmgeo.csm.jmu.edu/geollab/Fichter/PlateTect/heathistory.html

* The Ring of Fire: (also referred to as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) Most of the active volcanoes on Earth are located underwater, along the aptly named “Ring of Fire” in the Pacific Ocean. Made up of more than 450 volcanoes, the Ring of Fire stretches for nearly 40,250 kilometers (25,000 miles), running in the shape of a horseshoe (as opposed to an actual ring) from the southern tip of South America, along the west coast of North America, across the Bering Strait, down through Japan, and into New Zealand.

The Ring of Fire is the result of plate tectonics. Much of the Earth's volcanic activity and earthquakes occur along subduction zones, which are convergent plate boundaries where two tectonic plates come together. The heavier plate is shoved (or subducted) under the other plate. When this happens, melting of the plates produces magma that rises up through the overlying plate, erupting to the surface as a volcano.

Pacific_Ring_of_Fire.png
Gringer (talk) 23:52, 10 February 2009 (UTC) - vector data

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Subduction zones are also where Earth’s deepest ocean trenches are located and where deep earthquakes happen. The trenches form because as one plate subducts under another, it is bent downward. Earthquakes occur as the two plates scrape against each other and as the subducting plate bends.

See: https://oceanexplorer.noaa.gov/facts/rof.html

See: https://earthquake.usgs.gov/earthquakes/byregion/

See: https://earthquake.usgs.gov/earthquakes/eventpage/nc72906781#map?

** Ocean vents sit over deep fissures in the ocean floor. Ocean vents ejecthot, often toxic, fluids and gases into the surrounding seawater. They often mark sites of tectonic activity, and create some of the most hostile habitats on Earth.

Ocean vents are a type of hydrothermal vent. Other types of hydrothermal vents include hot springs, geysers, and fumaroles. As their name indicates, all hydrothermal vents are characterized by water (hydro-) and extremely high temperatures (thermal).

Ocean vents are the product of tectonic activity beneath the ocean floor. Tectonic activity describes the way tectonic plates, giant slabs of Earth’s lithosphere, interact with each other.

Ocean vents are found in all ocean basins, although they are most abundant around the Pacific Ocean’s “Ring of Fire,” which also includes active earthquake zones, volcanoes, and ocean trenches.

Ocean vents are primarily found around mid-ocean ridges and volcanic arcs. At both mid-ocean ridges and back-arc basins, the molten magma of Earth's asthenosphere wells up close to the surface.

Mid-ocean ridges form at divergent plate boundaries, where tectonic plates are moving apart from each other. New oceanic crust is formed at mid-ocean ridges. The Mid-Atlantic Ridge, for instance, runs through the entire Atlantic Ocean, separating the North American and Eurasian plates in the north and the South American and African plates in the south. Ocean vents dot the entire underwater mountain range.

Volcanic arcs form at convergent plate boundaries, where a dense tectonic plate is falling beneath a less-dense plate in a process called subduction. Oceanic crust is being destroyed in the subduction zones around volcanic arcs. Volcanic arcs may include volcanoes that rise above sea level, such as Japan’s Ryuku Islands, while some volcanic arcs are seamounts, or underwater mountains.

Ocean vents are one of the primary determinants of ocean chemistry. (Other major contributors include runoff from rivers and atmospheric changes in the air.)

The ocean’s salinity, for example, was not fully understood until ocean vents were discovered in the 1970s. Prior to the discovery, most oceanographers suspected the ocean was salty due to sediments deposited by rivers and streams. Today, we know the ocean is salty because ocean vents eject chemicals directly in the water column.

While ocean vents help explain how chemicals such as salt are added to seawater, they can also help explain how chemicals are taken out. For decades, for example, oceanographers could not explain how the concentration of magnesium in the ocean remained constant. Magnesium was being added to seawater from terrestrial sources, but the chemistry of the ocean remained the same. The discovery of ocean vents solved the mystery: Volcanic rocks in the recharge and reaction zones extractmagnesium from seawater. The water coming out of the vents has virtually no magnesium in it.

While ocean vents contribute to the ocean’s chemistry, their profound heat only slightly influences ocean temperatures. The reason is that while vent fluids are super-hot, they are super-cooled by the tons of cold water surrounding them. In fact, beyond a meter (3 feet) of a vent, the water is back to a near-freezing 1.7° Celsius (35° Fahrenheit).

See: https://www.nationalgeographic.org/encyclopedia/ocean-vent/

*** Plate tectonic processes: The theory of Plate Tectonic Processes (PTP) (also called “Platonics”; see also “If not plumes – what else?”) proposes that volcanic anomalies are “by products” of plate tectonics. The most important elements are:

  1. intraplate deformation, that results from the non-rigidity of plates, and
  2. compositional variability in the upper mantle resulting from de-homogenising processes at ridges and subduction zones.
Simply put, volcanism occurs where lithospheric extension allows melt to leak up to the surface. The location of the volcanism is governed by the stress field in the plate and the amount of melt is governed by the fusibility of the mantle beneath. This theory views volcanism as resulting from lithospheric processes rather than from a heat influx from below, at the core-mantle boundary. It predicts that volcanic anomalies and their geochemistry are shallow sourced and related structures do not extend very deep into the mantle.

page3image2680529312
Schematic illustrations (not to scale) of two contrasting views of the chemical structure of the mantle. (a) The classical, layered mantle model. As a result of vigorous convection and mixing and formation of the continental crust, the upper mantle (its size not precisely de¢ned) is well homogenized, depleted, degassed and essentially isothermal, or adiabatic. Subducted slabs of oceanic crust and sediments (red) are convectively stirred with the depleted upper mantle reservoir (blue) on a relatively short time scale, or pass through on their way to the lower mantle. Deep subduction of slabs places some oceanic crust in the lower mantle or at the core^mantle boundary, where they age. This material can be recycled back into the upper mantle by deep-rooted mantle plumes originating at the core^mantle boundary or at a proposed thermal boundary layer in the mid-lower mantle. Deep- rooted mantle plumes funnel noble gases with primordial isotopic compositions into the upper mantle from an essentially unde- gassed lower mantle reservoir. Adopted from Hofmann [4]. (b) The statistical upper mantle assemblage model. The upper mantle is a heterogeneous assemblage of depleted residues (bluish colors) and enriched, subducted oceanic crust, lithosphere and sedi- ments (reddish colors). The heterogeneities are statistical in nature and have wide ranges in shape, size, age and origin. (See: )

Earth’s tectonic plates are in reality, not rigid. They move coherently, but deform internally in response to changes in stress that may result from changes in the plate boundary configuration. The Basin Range Province in the western USA and the East African Rift are examples. Basin Range extension in the western USA onset in the late Cenozoic when the North American plate overrode the East Pacific Rise and the plate boundary there changed from being subduction to transform type (see animations). The East African rift formed at ~ 30 Ma, when the eastern boundary of the African plate changed as a result of a ridge jump in the Indian Ocean [Burke, 1996]. Intraplate deformations are most likely to occur along old sutures or other lines of weakness, e.g., at Yellowstone.

PTP, or Plate Tectonic Processes, theory offers a unifying theory of volcanism and convection in Earth’s mantle. In the framework of plume theory, two separate, independent modes of convection are proposed – plate tectonics on the one hand, accounting for volcanism at subduction zones and spreading plate boundaries, and plumes on the other, to which intraplate volcanism is attributed. On-ridge volcanic anomalies, with their spectrum of variability from large-volume, long-lived features to small-volume, short-lived phenomena, or even mere isolated ridge segments with slightly more OIB-like geochemistry, sit uneasily in between, along with the plethora of mid-ocean seamounts, many unassociated with time-progressive lineations but nevertheless also capped with OIB. The present theory suggests that there is only one mode of convection in Earth – that driven by plate tectonics, and that this can explain most volcanism on Earth, including that currently attributed to plumes.

See: http://www.mantleplumes.org/PTProcesses.html

You see, we are in a race. We are in a contest to save the human race. All the petty squabbles among men and nation states must be solved and we must reach the stars, or at least the outer solar system, before our planetary core dies or our entire planet is subsumed by our own dying red giant star. The countdown clock is running. As President John F. Kennedy said, "We choose to do it, not because it is easy, but because it is hard." We have no other choice.
Hartmann352
 
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Gregg95

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Jul 7, 2021
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After 4.5 billion years, the inside of the Earth is still very hot (in the core, approximately 3,800°C – 6,000°C), and we experience phenomena generated by this heat, including earthquakes, volcanoes, and mountain building.
 
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Jan 27, 2020
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After 4.5 billion years, the inside of the Earth is still very hot (in the core, approximately 3,800°C – 6,000°C), and we experience phenomena generated by this heat, including earthquakes, volcanoes, and mountain building.
Yes, you are correct, and in another 4-5 billion years the Earth's internal heat engine will run out of fuel and cool down at just about the same time as our sun becomes a red giant on the main sequence of stellar evolution for a typical type G2 star. And the red giant's gaseous envelope will envelope the Earth.
Hartmann352
 
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