EARTH'S INTERIOR
LAYERS OF THE EARTH CRUST 6-45 miles thick above sea level 2-7 miles thick on ocean floor Thinnest and least dense layer Composed of igneous rock
MANTLE Approximately 1,790 miles thick Includes both brittle and molten layers Temperatures reach nearly 6800°F Heat increases with depth
OUTER CORE App 400 miles thick of molten metal, Comp iron and nickel
INNER CORE 750-mile radius Solid due to pressure Composed primarily of iron Temperatures reach more than 10,000°F
Novelist Jules Verne imagined journeying to the center of the Earth in his 19th-century science fiction classic by that same name, but no human has really ventured deeper than Earth' crust-let alone all the way to the core at it center. Extremes of temperature and pressure make the a most 4,000-mile undertaking impossible. The deepest min shaft extends no more than 2. eltes beneath Earth's surface Interior sample drilling has penetrated only 8 miles down
Scientists gather information about Earth's interior by recording, imaging, and measuring vibrations, or seismic waves, caused by earthquakes or explosions. The moverments and the speed of seismic waves as they travel
through Earth provide data that in- form us about the composition and structure of Earth's interior. Earth may have started out as a cold planet and heated us, or it may have peen a molten planet that eventually
cooled on the outside. Scientists do not yet agree on those points. Either way, complex geologic events created the present structure of Earth's core The inner part of the core is made earth's of superhot, iron-rich material. The at its temperature there may be as high as 10,000°F, as hot as scientists be- mine lieve it gets on the surface of the sun. The pressure on the inner core face. is so intense that it remains solid and own. does not melt, despite such high temperatures.The outer part of the core likely is molten iron and nickel The entire core is some 4,350 miles in diameter, more than half of Earth's diameter. Studies of Earth's interior suggest that the outer boundary of the core may be irregular, much like Earth's surface.
A SEISMOGRAM graphe Earth's motions through time, sensed by a seismograph, an instrement with electromagnetic sensors that detect movement in the Earth's surface. This seismogram shows a single earthquake tremor detected at three different locations.
Croatian physicist Andrija Mohorovičić (1857-1936), one of the first scientists to use seismographic equip- study earthquakes, noticed that some seismic waves arrived at his observatory earlier than anticipated. mantel to From this, he calculated that Earth's crust and mantle had 83 different densities. As seismic waves reach the denser mantle, they speed up. In his honor, the transition zone where this speedup occurs is named the Mohorovičić, or Moho, discontinuity. Seismic waves also undergo changes in speed in the transition zone between Ears mantel and the outer core. This zone is named Gutenberg discontinuity, honoring American physicist Beno Gutenberg (1889-1960), who helped Charles Richter develop the Richter scale.
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