Earth’s Composition and Processes

A Look Inside The Earth

How has our planet changed over time?

What has caused change to the earth’s surface?

Essential Questions

Section One Earth’s Interior

Earth’s surface is constantly changing

The surface has been lifted up, pushed down, bent, and broken

The earth is much different today than it was millions of years ago.

Exploring Inside Earth

What are some ways that earth’s surface has changed?◦ Earthquakes ◦ Erosion ◦ Flooding ◦ Glaciers

Exploring Inside Earth

The extreme conditions that are within the earth’s interior prevent exploration far below the surface.

Geologist have used two main types of evidence to learn about earth’s interior:◦ Direct observation- rock samples◦ Indirect observation - seismic waves

Exploring Inside Earth

Why would a geologist study the interior of a cave?◦ To examine the materials that below ground ◦ To find out how a cave is formed

What is a limitation of studying a cave to learn about the interior of Earth?◦ Even the deepest caves only extend a short

distance into the earth’s crust

Exploring Inside Earth

Geologist drill holes and bring up rock samples. From these samples geologists:

◦ Make inferences about conditions from within the earth

◦ Infer where these rocks formed ◦ Provide information about the interior of the earth

Evidence From Rocks

To study the interior of the earth geologists use an indirect method, seismic waves.

Seismic Waves- vibrations that travel through the earth carrying energy released by earthquakes

Geologists study how the they travel through the earth.

Evidence From Seismic Wave

The speed of the seismic waves and the path they take reveal the structure of the planet

Using information geologist have gathered indicates that the earth’s interior is made of several layers

Evidence From Seismic Waves

The three main layers of earth are the crust, the mantle, and the core. These layers vary greatly in size, composition, temperature, and pressure

A Journey to the Center of Earth

There is a steady increase in temperature as you travel from the surface to the center of the earth

The high temperatures inside the earth are the result of heat left over from the formation of the planet.

Radioactive substances inside the Earth release energy, that further heats in the interior

Temperature

What general statement can you make about the change in temperature through Earth’s interior?

◦ Temperature increases as depth increases

Temperature

As you move from the surface to the interior of the earth the pressure around you will increase steadily.

Pressure results from a force pressing on an area

Pressure

Because of the weight of the rock above, pressure inside the earth increases the deeper into the earth you go.

Example:◦ Similar to diving deep into a swimming pool

Why does pressure increase with depth?

◦ Pressure increases toward Earth’s center because more rocks lies above the center

Why does temperature increase?◦ Earth became very hot when it formed. Some of

this heat remains. The decay of radioactive elements also contributes heat to earth’s interior

The Crust is the layer of rock that forms Earth’s outer skin.

The crust is a layer of solid rock that includes both dry land and the ocean floor

The Crust contain:◦ Mountains ◦ Soil ◦ Rocks ◦ Water

The Crust

Thickest under a mountain Thinnest under the ocean

The crust under the ocean is called oceanic crust, consists mostly of basalt

The Crust

Basalt is a dark rock with a fine texture

Continental Crust, the crust that forms the continents, consists mainly of rocks of granite

Granite is a rock that usually is light in color and has a coarse texture

The Crust

Which type of crust, continental or oceanic, is the thickest?◦ Continental crust

What is the main type of rock in oceanic crust?◦ Basalt

About 40 kilometers beneath the surface, you cross a boundary. Below the boundary is the mantle.

Mantle is a layer of hot rock

The Mantle

Earth’s mantle is made up of rock that is very hot, but solid .

Scientists divide the mantle into layers based on the physical characteristics of those layers

Overall the mantle is almost 3,ooo km thick

The Mantle

Uppermost part of the mantle

Very similar to the crust

Average thickness is about 100 km

Rigid layer

The Lithosphere

Less rigid

This layer is somewhat soft because of the heat

Softer then the rest of the mantle, its still solid

The Asthenosphere

Solid

Extends to the earth’s core

The Lower Mantle

The Core is mad of mostly metals: irons and nickel. It consists of two parts- a liquid outer core and a solid inner core

The Core

Outer core is a layer of molten metal that surrounds the inner core.◦ is a liquid

Inner core is a dense ball of solid metal◦ The pressure squeezes the metals so much they

cannot spread out and become a liquid

Outer and Inner Core

Scientists think that the movement in the liquid outer core creates earth's magnetic field

Just as a bar magnet is surrounded by its own magnetic field, earth’s magnetic field surrounds the planet

The Core and Earth’s Magnetic Field

Section Two Convection and the Mantle

Heat always moves from a warmer substance to a colder substance through heat transfer

There are three types of heat transfer:◦ Radiation ◦ Conduction ◦ Convection

Types of Heat Transfer

The Transfer of energy through space is called radiation

Takes place with no direct contact between the heat source and an object

The sunlight heating the earth is one example

Radiation

Heat transfer within a material or between materials that are touching is called conduction

In conduction, the heated particles of a substance transfer heat through contact with other particles in the substance.

Conduction

Conduction is responsible for some of the heat transfer inside the Earth.

What are some examples of radiation?◦ Heat from a Stove ◦ Warmth from the sun ◦ Heat from a fire

Conduction

What are some examples of conduction?◦ Burning your feet on a hot beach◦ Warming sore muscles with a heating pad ◦ Having cold hands after making a snow ball

Conduction

Heat can be transferred by the movement of liquids ands gases.

Convection is heat by the movement of currents within a fluid

Convection

During convection, heated particles of fluid begin to flow

The flow transfers heat from one part of the fluid to another

Heat transfer by conviction is caused by differences of temperature and density within a fluid.

Convection

Density is a measure of how much mass there is in a volume of a substance.

when gases or liquids are heat particles spread apart and occupy more space, so the density decreases

Conviction

Convection Current is the flow that transfers heat within a fluid.

Heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion

Convection currents continue as long as heat is added.

Convection Currents

Heat from the core and the mantle itself causes convection currents in the mantle.

Convection currents rise and sink through the mantle

These convection currents cause the earth’s magnetic field

Convection Currents in Earth

Drifting Continents Section Three

In 1910 Alfred Wegener hypothesized that all the continents were once joined together in a single landmass and have all since drifted apart.

The idea that all the continents moved over earth’s surface become known as continental drift

Continental Drift

According to Wegener, the continents drifted together to form a supercontinent called Pangaea

Continental Drift

Millions of years ago, Pangaea began to break apart. The pieces started moving to their present day location.

Wegener gathered evidence from different scientific fields to support his idea about continental drift. He studied land features, fossils, and evidence of climate change.

Continental Drift

When Wegner pieced together maps of Africa and South America, he noticed that mountain ranges on both continents line up.

He also noted that coal fields match up with coal fields in North America

Evidence From Land Features

Wegener used fossils to support his hypothesis.

Fossils of the same species have been found in Africa, South America, Australia, India, and Antarctica ◦ These areas are now multiple oceans

Evidence From Fossils

As a continent moves toward the equator, its climate becomes warmer.

As a continent moves toward the poles, its climate becomes colder.

Some places that are now very warm, at one time in history, had glaciers covering them.

Evidence from Climate

Wegener attempted to explain how continental drift took place.

Unfortunately, Wegener could not provide a satisfactory explanation for the force that pushes or pulls the continents

Wegener’s Hypothesis Rejected

Wegener proposed that when continents collide, their edges crumple and fold.

The folding continents push up huge mountains

Wegener’s Hypothesis Rejected

Sea-Floor Spreading Section Four

Were does magma from Earth’s interior flow out onto the surface?◦ At volcanoes

What causes the lava to harden?◦ It hardens as it cools

Background

An underground mountain chain where new ocean floor is produced is a mid-ocean ridge.

In the mid 1900s scientists mapped the ocean using sonar

Sonar is a device that bounces sound waves off underwater objects and then records the echoes. The time it takes for the eco to arrive indicates the distance to the object.

Mid-Ocean Ridges

Look at figure 15

What is unusual about Iceland?◦ A mid-ocean ridge cuts through Iceland

In 1960, Harry Hess, an American Geologist, proposed a radical new idea. He suggested a process called sea floor spreading.

In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added.

As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

What is Sea-Floor Spreading ?

1. Sea floor spreading begins on a mid-ocean ridge.

2. Along the ridge, molten material that forms several km. beneath the surface rises and erupts

3. The older rock moves outward on both sides of the ridge

4. As the molten material cools, it forms a strip of solid rock in the center of the ridge

What is Sea-Floor Spreading?

Evidence to support Hess’s theory:◦ Eruption of molten material ◦ Magnetic strips of rock of the ocean floor ◦ Ages of the rocks

Evidence the Sea Floor is Spreading

In the 1960s scientists found rocks on the bottom of the ocean shaped like pillows.

Such rocks only form when molten materials harden quickly after erupting under water

These rocks showed that molten material has erupted again and again along the mid ocean ridge.

Evidence From Molten Material

Remember the earth behaves like a giant magnet

Throughout history earths magnetic poles have been reverse, the last time was 780,000 years ago

Scientists discovered that the rocks make up the ocean floor lie in a pattern of magnetized “stripes”

Evidence From Magnetic Strips

These stripes hold a record of reversal in earth’s magnetic field.

The rock began as molten material that cooled and hardened.

As the rock cooled, the iron bits inside lined up in the direction of Earth’s magnetic poles.

This locked the iron bits in place, giving the rocks a permanent “magnetic memory”

Evidence From Magnetic Stripes

Using a sea drilling ship, scientists sent pipes 6 km deep.

Samples were brought up through the pipes.

Then scientists determined the age of the rocks in the samples.

Evidence From Drilling Samples

Scientists found that the farther away from a ridge the samples were taken, the older the rocks were.

The youngest rocks were always in the center of the ridges, showing that the sea-floor spreading really takes place.

Evidence From Drilling Samples

How can the ocean floor keep getting bigger and bigger?

◦ The ocean floor doesn’t keep spreading. Instead, the ocean floor plunges into deep underwater canyons called deep-ocean trenches . The ocean crust bends downward.

Subduction at Trenches

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches

Subduction of Trenches

The process by which ocean floors sink beneath a deep-ocean trench and back into the mantel is called subduction

As subduction occurs, crust closer to mid-ocean ridge moves away from the ridge and toward a deep ocean trench.

The Process of Subduction

Subduction and sea-floor spreading can change the size and shape of the ocean.

About every 200 million years the ocean floor is renewed.◦ That is the time that it takes for new rocks to form

at the mid-ocean ridge and move across, and sink into a trench

Subduction and the Earth’s Ocean

The Theory of Plate Tectonics

Section Five

A Canadian Scientist J. Tuzo Wilson observed cracks in the continents.

According to Wilson the lithosphere is broken into separate sections called plates

Wilson combined what geologists knew about sea-floor spreading, earth’s plate, and continental drift into a single theory

Background Info.

The theory of plate tectonics states tat pieces of Earth’s lithosphere are in slow, constant motion, driven by convection currents in the mantle.

The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates.

How Plates Move

Geologist think that the major force that causes movement of plates is the convection currents in the mantle of the earth.

How Plates Move

During subduction, gravity pulls one edge of a plate down to the mantle. The rest of the plate also moves.

As plates move the collide, pull apart, or grind past each other, producing changes to earths surface such as:◦ Volcanoes ◦ Mountains ◦ Deep ocean trenches

How Plates Move

The edges of Earth’s plates meet at plate boundaries

Faults are breaks in the earths crust where rocks have slipped past one another.

There are three kinds of boundaries: divergent, convergent, transform boundaries

Plate Boundaries

Divergent boundaries also occur on land.

When a divergent boundary develops on land, two of earth’s plates slide apart.

A deep valley called a rift valley forms along the divergent boundary

Divergent Boundary

The place where two plates come together, or converge, is called a convergent boundary.

When two plates converge, the result is called a collision

When two plates collide the density of the plates determines which one comes out on top.

Convergent Boundary

Neither piece of crust is dense enough to sink very far into the mantle

The result is the formation of mountain ranges

Convergent Boundaries

Transform Boundary is a place where two plates slip past each other, moving in opposite directions.

Earthquakes occur along these transform boundaries

Crust is neither created nor destroyed

Transform Boundaries