a look inside the earth. how has our planet changed over time? what has caused change to the...
TRANSCRIPT
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