How the Earth works lecture 2: Journey to the centre of the Earth

Question 1

Describe the magnetic field of Earth

Answer 1

Earths magentic field is like a giant dipole bar magnet

Question 2

Define the Heliosphere

Answer 2

Charged particles constantly flow away from the sun ( solar wind ).

Which forms a bubble around the sun. This is impeded by interstellar wind.

Question 3

Define the magnetosphere

Answer 3

Magnetic field extends into space, weakens with distance.

The magnetosphere protects the Earth from solar winds.

Question 4

Define and explain solar winds

Answer 4

Solar wind is a stream of energized, charged particles, mainly protons and electrons flowing out from the Sun.

-At speeds of up to 900 km per hour
-Temperatures of 1000C.

If the solar wind was not deflected this could result in significant increases in radiation on Earth.

Question 5

What are the sections of the Earth system?

Answer 5

Atmosphere—the gaseous envelope.

Hydrosphere—the blue liquid water.

Cryosphere—the frozen world.

Biosphere—the wealth of life.

Lithosphere—the solid Earth

Question 6

Desrcribe the makeup of the Atmosphere

Answer 6

Nitrogen (N) – 78 %
Oxygen (O) – 21 %
Argon (Ar) – 1 %

CO2 – 416 ppm

Question 7

Describe the Earth’s elemental composition

Answer 7

95.4% of Earth comprises 4 elements:
Iron 35%,
oxygen 30%,
silicon 15%,
magnesium 13%,
nickel 2.4 %

The remaining 4.6 % all other naturally occurring elements

Earth’s most abundant mineral – Bridgmanite (MgSiO3)

Question 8

Define a rock

Answer 8

Rocks - aggregates of minerals or grains.

Question 9

Define:

Igneous rocks

Sedimentary rocks

Metamorphic rocks

Answer 9

Igneous - cooled from a liquid (melt)

Sedimentary - debris cemented from preexisting rock

Metamorphic - rock altered by pressure and temperature

Question 10

Describe igneous rock key words:

Answer 10

Igneous rocks – building blocks of the planet

Melts - rocks that have been heated to a liquid

Magma - molten rock beneath the surface

Lava - molten rock at the surface
Volatiles - materials that turn into gas at the surface

H2O, CO2, CH4 and SO2
Volatiles are released from volcanic eruptions

Question 11

Define an ore deposit

Answer 11

Concentrations of rare materials and minerals

Question 12

Define industrial materials

Answer 12

Rocks, minerals and sediments with major uses.

Question 13

Describe the density of the Earth
As well as the density of the various layers

Answer 13

Henry Cavendish (1798) – Earth’s density 5.448 times that of water (only 1 % from modern value!).

In 1896, Emil Wiechert published first verifiable model of Earth’s interior as a series of shells
Earth is like an egg
Thin, light crust (eggshell)
Thicker, more dense mantle (eggwhite)
Innermost, very dense core (yolk)

Question 14

Define an Earthquake

Answer 14

Earthquakes: seismic energy from fault motion.

Question 15

Describe the crust

Answer 15

The outermost “skin” of our planet

Thickest under mountain ranges (70 km)
Relatively thin under oceans (5-8 km)

The Mohorovičić discontinuity (Moho) is the base.

two kinds of crust:
Continental crust:
-underlies the continents
-Average density of ~2.7 g/cm3
-Average thickness 35–40 km
-Close to the common rock type granite in composition

Oceanic crust:
-underlies the ocean basins
-Average density of ~3.0 g/cm3
-Average thickness 7–10 km
-Close to the common rock type basalt in composition

Question 16

Describe the mantle

Answer 16

Solid rock, 2,885 km thick, 82% of Earth’s volume.

The mantle is entirely the rock peridotite

Convection below 100 km mixes the mantle.

Convection: hot rises, cold sinks
Convection aids tectonic plate motion

Question 17

Describe the core

Answer 17

An iron-rich sphere with a radius of 3,471 km.

Seismic waves show two parts

Outer core is liquid:
Liquid iron-nickel-sulfur
2,255 km thick
Density is 10-12 g/cm3

Inner core is solid:
Solid iron-nickel alloy
Radius of 1,220 km
Density is 13 g/cm3

Outer core flow generates Earth’s magnetic field