Unit 3 Our Earth Mr Ross Brown Brooklyn

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/cm 3 • Ordinary rock is 3 g/ cm 3, iron is 8 g/ cm 3

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: 5 km-10 km thick – Continental Crust: 15 km-80 km 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, 900 km 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 April 2016 • 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: O 3 • 25 km (80, 000 feet) in Stratosphere • Ultraviolet photons make O 2 vibrate energetically, splitting apart. They join with other O 2 and form O 3. • O 3 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 (CH 4) and ammonia (NH 4)? (Like in volcanoes) – Solar radiation? • Where did the Oxygen (O 2) 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.