Transcript 1-Unit4Part1EarthsInterior

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)
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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 density
b) 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 crust
c) 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 Structure
Division 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)