Earth: Surface to Core

Facts in Brief

Mass	5.98 x 10²⁴ kg
Diameter	12,756.28 km
Density	5,515 kg/m³
Mean Surface Temperature	15^oC
Surface Gravity	9.78 m/s²
Orbital Eccentricity	0.0167
Surface Pressure	1.014 bars
Magnetic Field	0.3076 gauss-Re³

Hydrosphere

The hydrosphere technically contains all the water on Earth but is commonly defined to include only oceans. The oceans account for 1.35 x 10²¹ kg of the total Earth mass of 5.98 x 10²⁴ kg. They measure a depth of 3,794 m.

Lithosphere, Mantle, and Core

     Much of what is known about the Earth comes from the branch of science termed seismology. Researchers in this field often use waves to conduct their studies. By measuring both natural and artificially-produced waves, they can better understand the Earth's structure and composition. The lithosphere is the uppermost layer, including the upper mantle and crust. It is divided into 7 large and 7 small tectonic plates. (See Tectonic Plate Theory.) The lithosphere is comprised of many elements, most of which are in a compound form and crystalline state. Oxygen takes the lead with 46.6%, followed by silicon at 27.72%. Aluminum (8.13%), iron (5%), calcium (3.63%), sodium (2.83%), potassium (2.59%), and magnesium (2.09%) are also present. Bringing up the rear (from most to least) include carbon, manganese, sulfur, barium, chlorine, chromium, fluorine, zirconium, nickel, strontium, and vanadium.
     The crust is characterized as dark, rocky, and rigid and is further broken down into the upper and lower crusts. The sialic, or upper crust, is what makes up the continents. They are mostly igneous and sedimentary. The simatic, or lower crust, forms the ocean floors. Beneath the crust is denser material composed of iron and magnesium silicates. This region is known as the upper mantle and accounts for 10.3% of Earth's total mass. It is separated from the crust and lower mantle by the Moho and asthenosphere, respectively. The Moho averages 32 km under the continents and a meager 8 km in depth under the oceans. The asthenosphere is noticeably thicker at several hundred kilometers in depth. It is mostly deformable rock.
     As expected, the material closer to the Earth's core is more closely packed, or dense. The lower mantle is the layer directly beneath the lithosphere, which comprises a whopping 49.2% of the Earth's mass. It is found 650 to 2,890 km beneath the surface and is a mixture of several oxides. These include magnesium, silicon, and iron.
     The core is the central spherical region within the Earth and is further divided into the outer and inner cores. The outer core has a shell 2,890 to 5,510 km beneath the surface and accounts for 30.8% of the planet's mass. Studies indicate that it is rigid with both peaks and depressions. The solid inner core has radius 1,275 km and is 1.7% of the Earth's mass. The inner core's temperature may be a scorching 6,650 degrees Celsius. The entire core is mostly iron with a small percentage of nickel and other elements. The internal heat generated here is possibly energy emitted from radioactive decay of uranium and other elements found in the core. Convection currents within the mantle transfer this heat to the surface. These currents may also be the source of continental drift.

Copyright © 2000 by Gary Chan and Matthew McDermott. All rights reserved.