The Structure of the Earth

Internal Structure and Heat

Reminders

• 4.6 billion years ago earth formed– Gas and dust collected inward by the pull

of gravity

• Earth grew – Accretion occurred– Earth’s gravity pulled in small

planetismals and meteorites – Called the Cold Accretion Theory

Video: What’s Inside the Earth: An Introduction to the Earth’s Interior Crust and Mineral Resources (25 min)

• C:\Documents and Settings\lisa.perley\Desktop\SPhysicalGeography\Unit4EarthsInterior\What_s_Inside_the_Earth___An_Introduction_to_the_Earth_s_Interior__Crust__and_Mineral_Resources.asf

Question Sheet• 1. Scientists are able to measure to

determine what’s inside the earth by analyzing shock waves as they travel through the earth.

• 2. Earth’s interior layers: inner core, outer core, mantle and outer shell

• 3. Plates• 4. Cracks in the earth’s crust.• 5. Earthquakes are caused by sudden

movement along a fault.• 6. Form of seismic waves

Question Sheet – cont’d

• 7. Fault block mountains• 8. Folded mountains• 9. Lava before it reaches the earth’s

surface.• 10. Lava that erupts through a large crack

in the earth’s surface in the form of a curtain.

• 11. Igneous rock• 12. Metamorphic rock

In Class Activity

• Read p. 51 to 52 (Planet Earth)

• Identify 3 sources of heat that led to the formation of the Earth’s hot interior

• Copy Figure 4.1 a– Radioactive decay: A major source of energy from below

• Copy Figure 4.1 b– Radioactive Elements in the Earth’s Interior

Sources of Internal Energy

• 3 Sources of Energy that led to the Earth’s hot interior:

1) Kinetic energy of moving bodies striking the Earth (think meteorite impacts)

2) Compression of rock materials due to enormous pressure from material above

*3) The decay of unstable, radioactive elements within the rock of the earth

* This continues to be the major source of heat . Uranium, thorium, potassium

• Table 4.1b– Long term radioactive elements believed

to still be decaying today• Uranium 238• Uranium 235• Thorium 232• Potassium 40

Question:

• Question: Explain why the Earth’s interior will eventually cool and become solid, like the interior of the moon.

• Answer: 1) The long-term radioactive elements will eventually run out. 2) Once there is no more fuel, the heat source will be gone and the cooling will begin. When things cool, they will solidify.

Earth’s Internal Heat

• No one really knows the temperature of the Earth’s center– Key:

• Temperature and pressure increase with depth• Rate at which temperature increases with depth is known• Thus can be calculated mathematically

– Mantle: 870 degrees Celsius– Outer core: 4400 degrees Celsius– Inner core: 7000 degrees Celsius

A Layered Earth: Internal Structure• Earth: diameter about 12, 750 km

• 3 Main layers:– Crust

• Compared to an egg: Egg shell

– Mantle• Compared to an egg: Egg white

– Core• Compared to an egg: The Yolk

Crust

• Outermost layer • Rigid and thin compared to the other two• Ranges from 0 to 100 km thickness

– Oceanic Crust• Beneath the ocean – about 5 km thickness

– Continental Crust• Beneath the continents – average 30 – 40 km thickness• Beneath the mountains – as deep as 100 km thickness

Mantle

• Two parts: upper (outer) and lower (inner) mantle• Dense, hot layer of semi-solid rock approximately

2900 km thick• Described as a solid that flows• Contains more magnesium, calcium and iron than

the crust• Hotter and denser because temperature and

pressure increases with depth

Core

• Center• Twice as dense as the mantle• Two distinct parts

– Outer core• 2200 thick liquid

• Molten Fe (iron) and Ni (nickel)

– Inner core• 1250 km thick solid

• Solid Fe with some Ni

Structure of the Earth

How did the layers form?

- Look at Table 4.2- These are the major elements that make up

the Earth- The higher the mass, the greater the

density- What is the element with the highest

density and the greatest percentage?- Iron

- Where do you find iron?- Inner / outer core

Figure 4.2 Major Elements that make up Planet Earth

Formation of Layers cont’d

• In the beginning, states were molten / liquid– Differentiation took place

• Heavy elements moved inward (due to gravity) towards the core

• Lighter elements moved outward towards to the crust

• Time: few 100 million years

Differentiation of Early Earth

a) early Earth (4.6 b.y.) had uniform composition and densityb) heat generated by gravitational contraction, collisions with debris in its orbital path and decay of radioactive elements results in (partial) melting; during molten phase dense elements sink to collect in core and lighter silicate minerals flow upward to form mantle and crustc) differentiation results in layered planet, and emission of gases supplies material for early atmosphere and oceans

Composition of Layers• Crust

– Oceanic Crust – basically basalt ^basalt – very liquid lava that has cooled quickly

Note: The majority of the crust has been made through volcanic activity

– Continental Crust• Upper part: basically granite• Lower part: basalt and diorite

• Mantle– Upper / outer Mantle – liquid rock, mainly silicates of iron and

magnesium– Lower / inner Mantle – solid, mainly sulphides and *silicates of

silicon and oxygen*silicate – minerals that contain mostly silicon, oxygen and other minerals

• Core– Inner Core – solid, mainly iron and nickel– Outer Core – liquid, mainly iron and nickel

Earth’s Layered StructureDivision by Physical Properties

1. Lithosphere – Rigid, outermost layer

• Made up of the crust and the upper part of the mantle

– Averages 80 km thickness over the Earth– Two types of lithosphere

• Oceanic lithosphere• Continental lithosphere

– Divided into dozen or so rigid plates that move relative to one another

– “Plate” of Plate Tectonics

Lithosphere

2. Asthenosphere– 100 to 700 km deep– Relatively narrow, mobile zone in the upper

mantle below the lithosphere– Composed of hot, semi-solid material which can

soften and flow (subjected to high temperatures and pressures over geologic time)

– Undergoes convection (circulates)

• Believed that the lithosphere floats or moves about the asthenosphere– The convection of the asthenosphere is what

moves the plates

3. Mesosphere (middle / lower mantle)• Found between the asthenosphere and

the outer core• Largest layer of the earth• More solid than the asthenosphere due

to higher pressures

• Video: Forces that shape the earth (28 minutes)