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The geographical centre of Earth is the geometric centre of all land surfaces on Earth. Geometrically defined it is the centroid of all land surfaces within the two dimensions of the Geoid surface which approximates the Earth's outer shape.
In geography, the centroid of the two-dimensional shape of a region of the Earth's surface (projected radially to sea level or onto a geoid surface) is known as its geographic centre or geographical centre or (less commonly) gravitational centre.
- Scientific History
- Data Sources
- Physical Properties
- Composition
- Structure
- Growth
- Dynamics
- Age
Earth was discovered to have a solid inner core distinct from its molten outer core in 1936, by the Danish seismologist Inge Lehmann, who deduced its presence by studying seismograms from earthquakes in New Zealand. She observed that the seismic waves reflect off the boundary of the inner core and can be detected by sensitive seismographs on the Ea...
Seismic waves
Almost all direct measurements that scientists have about the physical properties of the inner core are the seismic waves that pass through it. The most informative waves are generated by deep earthquakes, 30 km or more below the surface of the Earth (where the mantle is relatively more homogeneous) and recorded by seismographs as they reach the surface, all over the globe.[citation needed] Seismic waves include "P" (primary or pressure) waves, compressional waves that can travel through soli...
Other sources
Other sources of information about the inner core include 1. The magnetic field of the Earth. While it seems to be generated mostly by fluid and electric currents in the outer core, those currents are strongly affected by the presence of the solid inner core and by the heat that flows out of it. (Although made of iron, the core is not ferromagnetic, due to being above the Curie temperature.)[citation needed] 2. The Earth's mass, its gravitational field, and its angular inertia. These are all...
Seismic wave velocity
The velocity of the S waves in the core varies smoothly from about 3.7 km/s at the center to about 3.5 km/s at the surface. That is considerably less than the velocity of S waves in the lower crust (about 4.5 km/s) and less than half the velocity in the deep mantle, just above the outer core (about 7.3 km/s).: fig.2 The velocity of the P-waves in the core also varies smoothly through the inner core, from about 11.4 km/s at the center to about 11.1 km/s at the surface. Then the speed drops abr...
Size and shape
On the basis of the seismic data, the inner core is estimated to be about 1221 km in radius (2442 km in diameter),which is about 19% of the radius of the Earth and 70% of the radius of the Moon. Its volume is about 7.6 billion cubic km (7.6 × 1018 m3), which is about 1⁄146(0.69%) of the volume of the whole Earth. Its shape is believed to be close to an oblate ellipsoid of revolution, like the surface of the Earth, only more spherical: the flattening f is estimated to be between 1⁄400 and 1⁄41...
Pressure and gravity
The pressure in the Earth's inner core is slightly higher than it is at the boundary between the outer and inner cores: It ranges from about 330 to 360 gigapascals (3,300,000 to 3,600,000 atm). The acceleration of gravity at the surface of the inner core can be computed to be 4.3 m/s2; which is less than half the value at the surface of the Earth (9.8 m/s2).
There is still no direct evidence about the composition of the inner core. However, based on the relative prevalence of various chemical elements in the Solar System, the theory of planetary formation, and constraints imposed or implied by the chemistry of the rest of the Earth's volume, the inner core is believed to consist primarily of an iron–ni...
Many scientists had initially expected that the inner core would be found to be homogeneous, because that same process should have proceeded uniformly during its entire formation. It was even suggested that Earth's inner core might be a single crystalof iron.
The Earth's inner core is thought to be slowly growing as the liquid outer core at the boundary with the inner core cools and solidifies due to the gradual cooling of the Earth's interior (about 100 degrees Celsius per billion years). According to calculations by Alfé and others, as the iron crystallizes onto the inner core, the liquid just above i...
Because the inner core is not rigidly connected to the Earth's solid mantle, the possibility that it rotates slightly more quickly or slowly than the rest of Earth has long been entertained. In the 1990s, seismologists made various claims about detecting this kind of super-rotation by observing changes in the characteristics of seismic waves passin...
Theories about the age of the core are necessarily part of theories of the history of Earthas a whole. This has been a long-debated topic and is still under discussion at the present time. It is widely believed that the Earth's solid inner core formed out of an initially completely liquid core as the Earth cooled down. However, there is still no fi...
30 de abr. de 2024 · Earth is the planet we live on, one of eight planets in our solar system and the only known place in the universe to support life. Earth is the third planet from the sun, after Mercury and Venus, and before Mars. It is about 150 million kilometers (about 93 million miles) from the sun.
26 de fev. de 2024 · It stands on the North Anatolian Fault, and is currently in an earthquake warning zone. The average elevation is approximately 985 meters above sea level. The provincial capital is Kırşehir. The geographical centre of all land surfaces on Earth is at 39°00′N 34°00′E, in Kırşehir Province, Turkey.
10 de abr. de 2022 · By NASA's Goddard Space Flight Center April 10, 2022. At the foundation of virtually all airborne, space-based and ground-based Earth observations is the TRF, or Terrestrial Reference Frame. The TRF relies on an accurate calculation of the geocenter of the Earth (the center mass of the Earth).
Há 5 dias · Earth, third planet from the Sun and the fifth largest planet in the solar system in terms of size and mass. Its single most outstanding feature is that its near-surface environments are the only places in the universe known to harbour life. It is designated by the symbol ♁.
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