Internal Structures of the Earth

mantle

contains melted silicon compounds

The earth's magnetic field is associated with the:

core

asthenosphere

semi-liquid region below the crust

In the past, the intensity of the earth's magnetic field was:

greater

In some places, granite rock extends as deep as:

50 kilometers

What percent of the earth's surface does the ocean cover?

75%

The four major components of the earth's crust are:

-hydrosphere -granite foundation -basalt ocean floor -sedimentary rock

Measurements of the earth's magnetic field have been recorded since:

1829

What is the result of rock's poor ability to transmit heat?

Cools very slowly

Interior Earth consists of:

Crust, mantle, outer core, inner core. The general structure and physical properties of the interior of the earth are inferred through the analysis of seismic waves. These waves are produced by the energy released during earthquakes. The path of seismic waves through the earth is recorded by a world-wide network of seismographs which are located at earthquake monitoring facilities. The path of the seismic waves may be traced from an earthquake's epicenter (point of origin) through the earth as they are received at numerous sites around the world.

What keeps Earth's core from melting?

Extreme high pressure from the weight of the layers of rock above it

What does the foundation of the continents mostly consist of?

Igneous granite rock

Shock waves (sonic booms)

Shock waves, started by earthquakes, produce two kinds of movement: compression waves, which push molecules closer together temporarily as they move away from the earthquake, and shearwaves, which move sideways. Compression shock waves move through both solids and liquids (faster through solids). Shearwave vibrations do not move through liquids. Vibrations from earthquakes show that the shearwaves get lost in a liquid zone about 2,900 kilometers under the surface. The compression waves that go through the planet are bent as they go in and out of this liquid outer core. They show that the middle part of the earth's core is solid.

What kind materials can compression shock waves move through?

Solids and liquids

Temperatures of the interior earth

Temperatures in the interior of the earth are so high that the rock would melt if the pressure were not so great. Radioactive atoms break up at a slow rate, keeping the temperatures high. Some mantle rock partially melts (only some minerals melt) and forces its way up to the surface. The minerals in the mantle that melt are the silicon compounds that make up the earth's crust. A small decrease in temperature would allow crystals to form and the rock to solidify. Rock is so poor at transmitting heat that it cools very slowly.

Earth's mantle

The body of rock from the crust down to the iron core of the earth is called the mantle. It is the second layer of the earth. The mantle is about 1,700 miles thick. It is made of rocks that contain more iron than rocks of the crust. Rock within the mantle gets heavier with depth until the melted outer core is reached. Within the mantle, at depths of about 80 to 160 kilometers, is a partially melted zone called the asthenosphere. The upward movement of rock through the fractures where it comes to the surface in volcanoes or remains under the surface indicates that partly or completely melted rock can be found at almost any depth. The passage of earthquake waves shows that most of the upper mantle is solid.

The Earth's Core

The innermost layer of the earth is called the core. The gravitational pull of the earth shows that the density of the earth is about five and a half times the density of the same volume of water. The density of rocks near the surface of the earth is only about three times that of water, so the interior must be made of much heavier materials such as iron and nickel. The earth's magnetic field shows that the core can hold or cause a strong magnetic field. Iron is the logical material.

The Earth's Magnetic Field

The origin and mechanism of the earth's magnetic field is not completely known. Scientists have several theories, but none are conclusive. Since 1829, the intensity of the magnetic field has been carefully measured. Analysis of this data indicates that the field strength is declining. A half life of the magnetic field is only 1,400 years (half of the intensity is lost every 1,400 years).

Earth's Crust

The outermost layer of the earth is called the crust. The average thickness of the earth's crust is 30 kilometers. It is made of the hydrosphere, sedimentary rock, granite foundation, and basalt floor. The hydrosphere is made of the water that covers about 75% of the earth. The average depth of the hydrosphere is about 4 kilometers. Sedimentary rock covers most of the continents and ocean basins. The average depth of the sedimentary rock is about ¾ kilometer. However, in some places the sedimentary rock is over 16 kilometers thick. The granite foundation averages 30 kilometers thick, although it can reach 50 kilometers under some mountain ranges. Granite is found under all the continents. The basalt floor is a layer of heavy rock found under the oceans. It averages about 5 kilometers thick.

hydrosphere

all the water that covers the earth

Much of the general structure and physical properties of the interior of the earth are inferred from:

analysis of seismic waves

The compression waves passing through the liquid outer core are:

bent

core

made of iron and nickel

crust

outermost layer