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Unit 3: Our Earth
Mr. Ross Brown
Brooklyn School for Law and
Technology
In this unit we will learn:
• How seismic waves teach us about earth’s
interior
• Understand earth’s chemistry and minerals
• Explain why the earth’s core is so hot
• Explain plate tectonics and how our earth’s
surface keeps changing
Aim: What is the earth made of?
• Date: 11 April 2016
• Do now: What minerals make up the crust of
the earth?
What are the size and shape of our
earth?
• Ancient Greeks discovered earth’s radius is
about 6,400 km (4,000 miles)
• Due to rotation, earth is not quite a sphere,
but an oblate spheroid, wider at equator.
What minerals compose our earth?
• Rocks are made of minerals, minerals are
made of chemical elements
• Most common on earth are oxygen (46%,)
silicon (28%,) aluminum, magnesium, and
iron.
• Silicon and oxygen typically occur as silicates
What are the size and shape of our
earth?
How is our earth composed?
• 12 April 2016
• Do now: Describe how interstellar explorers
would describe our earth upon first seeing it.
Write down your thoughts and share with
your tablemates.
The Earth in Space
Taken December 7, 1972, by the crew of the Apollo 17 spacecraft, at a distance
of about 45,000 kilometers (28,000 miles). (source: Wikipedia)
What does density tell us about
earth’s composition?
• Density: how much matter is in a given
volume
• Density of water: 1 gram/cm3
• Ordinary rock is 3 g/ cm3, iron is 8 g/ cm3
What are Earth’s Interior layers?
• Can’t see inside Earth, but scientists have
“seen” with seismic waves, vibrations
– Caused by earthquakes or explosions
• Earth has layers, or zones
– Crust: thin, solid, outermost layer
– 1% of earth’s mass
• Mass: the amount of matter in an object
– Oceanic Crust: 5km-10km thick
– Continental Crust: 15km-80km thick
What are Earth’s Interior layers?
• 15 April 2016
• Do now: Why are the Earth’s interior layers
different? What conditions inside the Earth
are responsible?
What are Earth’s Interior layers?
– Mantle:
•
•
•
•
•
2/3 of the earth’s mass
2,900km thick
Upper mantle is cool and brittle (lithosphere)
Due to heat and pressure, next layer of rock flows
Asthenosphere exhibits plasticity (solid that can flow)
– Core
• Center of the earth, composed mostly of iron
• Outer core is dense liquid layer
• Inner core is very dense and solid
Earth’s Interior layers
Inferred Properties of Earth’s
Interior
Seismic Wave Studies
• Two types of seismic waves
– P waves (primary) travel through liquids, solids,
and gases. Faster than S waves.
– S waves (secondary) travel only through solids.
– Core blocks seismic waves in shadow zones
Seismic Waves
Homework #7
• 12 April 2016
• Compare the behavior of P waves and S
waves.
How old is the Earth?
• 18 April 2016
• Do now: How old is the earth, and how do we
know that?
How hot is it inside the earth?
• Every km below the surface, temperatures rise
about 30°C
• Core is very hot, about 6,000°C, as hot as the
surface of the Sun
• Initially, heat was from impacts of colliding
bodies that formed the earth
• Earth is old, over 4 billion years. Radioactive
decay generates heat in the core.
How do we know the earth’s age?
• Radioactive decay of atoms found in rock
• Measured in half-life (how long for ½ to decay)
How has Earth taken its shape?
• 21 April2016
• Do now: What forces cause the continents to
move and drift?
How does convection shape our
earth?
• Convection: circulating movement of heated
material, like a pot of soup boiling
• Magma from earth’s core gets heated and
rises toward the crust
• As it nears the crust it spreads out and drags
the surface layers. This is rifting.
• In places, one piece of crust gets driven under
another, called subduction.
Rifting and Subduction
What is Plate Tectonics?
• The shifting of the geologic plates
• Earth’s lithosphere (rigid layer of crust and
outer mantle) gliding over inner mantle
• 7 or 8 major plates, several other minor
Earth’s plates
What happens where plates meet?
• Divergent Boundaries: plates move away from
each other, forming rifts or mid-ocean ridges
• Convergent Boundaries: plates collide
– Subduction: Oceanic pushed under continental
– Obduction: Continental pushed under oceanic
– Orogenic: both push upwards
• Transform Boundaries: Plates grind past each
other
Where plates meet
What happens where plates meet?
How does Earth’s atmosphere
make it different?
• 2 May 2016
• Do now: In what ways is Earth’s atmosphere
different than on other planets? In what ways
is it the same?
How does Earth’s atmosphere
make it different?
How does Earth’s atmosphere
make it different?
• About 480 km (300 miles) tall
• Troposphere: where you are. Only 20 km (12
miles,) but about ¾ mass of total atmosphere
and 99% of water vapor
• Stratosphere: up to about 50 km (30 miles)
• contains our ozone layer
• 78% Nitrogen (N) & 21% Oxygen (O)
What is the Greenhouse Effect?
How does Greenhouse Effect
protect us?
• Moon and Earth are Approximately same
distance from the Sun
• Earth average temperature: 59°F (15° C)
• Moon average temperature: -4° F (-20° C)
• Among our concerns: global warming
Homework #7
• 2 May 2016
• Explain how the Greenhouse Effect works
Why is our Ozone Layer so
important?
• Ozone: O3
• 25 km (80,000 feet) in Stratosphere
• Ultraviolet photons make O2 vibrate
energetically, splitting apart. They join with
other O2 and form O3.
• O3 absorbs ultraviolet.
• Ultraviolet is what burns you.
Ultraviolet and Infrared Radiation
How did our atmosphere
originate?
• Gases trapped in rocks?
• Comet impacts?
• And what happened to the methane (CH4)
and ammonia (NH4)? (Like in volcanoes)
– Solar radiation?
• Where did the Oxygen (O2) come from?
– photosynthesis
How does the earth’s rotation
affect the atmosphere?
• Coriolis effect: The earth’s rotation deflects
the ocean and air currents from their original
direction of motion.
• Much greater impact on faster-spinning
planets, like Saturn and Jupiter.
How do we know the Earth is
spinning?
• 4 May 2016
• Do now: What evidence do we have that the
Earth is spinning?
How do we know the Earth is
spinning?
• Léon Foucault
How do we know the Earth is
spinning?
How do we know the Earth is
spinning?
• Foucault Pendulum: simple device conceived
as an experiment to demonstrate the rotation
of the Earth
How do we know the Earth is
spinning?
• Foucault Pendulum
What’s this about the earth
wobbling?
• Precession: Over time, the direction in which
earth’s rotation axis points changes, like a
spinning top slowing down.