Impacts of Volcanic Hazards What are the principal signals of a volcanic unrest? How can we forecast volcanic eruptions? Tsunamis Where is a tsunami most likely to happen? Can Singapore be affected by a tsunami? Can animals sense an impending tsunami? What should we do during a tsunami? Why do trees seem to resist more to tsunamis than houses?
Why does a boat at sea experience a tsunami differently from a boat near the shore? Volcanoes All About Volcanoes What is the difference between magma and lava? Is lava always liquid? What does a magma chamber look like? What are the largest eruptions in the world? Are earthquakes and volcanic eruptions related? Where can we find volcanoes on earth? Miscellaneous Miscellaneous Why are there mass extinctions?
How did life appear on earth? How does photosynthesis work? What is GPS? What is gravity? What is the big bang? There are three main sources of heat in the deep earth: 1 heat from when the planet formed and accreted, which has not yet been lost; 2 frictional heating, caused by denser core material sinking to the center of the planet; and 3 heat from the decay of radioactive elements.
It takes a rather long time for heat to move out of the earth. This occurs through both "convective" transport of heat within the earth's liquid outer core and solid mantle and slower "conductive" transport of heat through nonconvecting boundary layers, such as the earth's plates at the surface.
As a result, much of the planet's primordial heat, from when the earth first accreted and developed its core, has been retained. The amount of heat that can arise through simple accretionary processes, bringing small bodies together to form the proto-earth, is large: on the order of 10, kelvins about 18, degrees Farhenheit. The crucial issue is how much of that energy was deposited into the growing earth and how much was reradiated into space. Indeed, the currently accepted idea for how the moon was formed involves the impact or accretion of a Mars-size object with or by the proto-earth.
When two objects of this size collide, large amounts of heat are generated, of which quite a lot is retained. This single episode could have largely melted the outermost several thousand kilometers of the planet. Additionally, descent of the dense iron-rich material that makes up the core of the planet to the center would produce heating on the order of 2, kelvins about 3, degrees F. The magnitude of the third main source of heat--radioactive heating--is uncertain.
The precise abundances of radioactive elements primarily potassium, uranium and thorium are poorly known in the deep earth. In sum, there was no shortage of heat in the early earth, and the planet's inability to cool off quickly results in the continued high temperatures of the Earth's interior. In effect, not only do the earth's plates act as a blanket on the interior, but not even convective heat transport in the solid mantle provides a particularly efficient mechanism for heat loss.
The planet does lose some heat through the processes that drive plate tectonics, especially at mid-ocean ridges. For comparison, smaller bodies such as Mars and the Moon show little evidence for recent tectonic activity or volcanism. We derive our primary estimate of the temperature of the deep earth from the melting behavior of iron at ultrahigh pressures.
We know that the earth's core depths from 2, kilometers to the center at 6, kilometers 1, to 3, miles , is predominantly iron, with some contaminants. The speed of sound through the core as measured from the velocity at which seismic waves travel across it and the density of the core are quite similar to those seen in of iron at high pressures and temperatures, as measured in the laboratory. Iron is the only element that closely matches the seismic properties of the earth's core and is also sufficiently abundant present in sufficient abundance in the universe to make up the approximately 35 percent of the mass of the planet present in the core.
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