Big Idea 6 Earth Structures

Benchmarks

SC.7.E.6.2 Identify the patterns within the rock cycle and relate them to surface events (weathering and erosion) and subsurface events (plate tectonics and mountain building). (Also assesses SC.6.E.6.1, SC.6.E.6.2, and SC.7.E.6.6.)

SC.6.E.6.1 Describe and give examples of ways in which Earth’s surface is built up and torn down by physical and chemical weathering, erosion, and deposition.

SC.6.E.6.2 Recognize that there are a variety of different landforms on Earth’s surface such as coastlines, dunes, rivers, mountains, glaciers, deltas, and lakes and relate these landforms as they apply to Florida.

SC.7.E.6.6 Identify the impact that humans have had on Earth, such as deforestation, urbanization, desertification, erosion, air and water quality, changing the flow of water.

SC.7.E.6.4 Explain and give examples of how physical evidence supports scientific theories that Earth has evolved over geologic time due to natural processes. (Also assesses SC.7.E.6.3.)

SC.7.E.6.3 Identify current methods for measuring the age of Earth and its parts, including the law of superposition and radioactive dating.

SC.7.E.6.5 Explore the scientific theory of plate tectonics by describing how the movement of Earth’s crustal plates causes both slow and rapid changes in Earth’s surface, including volcanic eruptions, earthquakes, and mountain building. (Also assesses SC.7.E.6.1 and SC.7.E.6.7.)

SC.7.E.6.1 Describe the layers of the solid Earth, including the lithosphere, the hot convecting mantle, and the dense metallic liquid and solid cores.

SC.7.E.6.7 Recognize that heat flow and movement of material within Earth causes earthquakes and volcanic eruptions, and creates mountains and ocean basins.

Layers of the Earth

The Earth is made of four main layers:

Crust: this is the outer most layer of the Earth. It contains both oceanic and continental crust.

Mantle: this layer is right beneath the crust. It is composed of three sections: the lithosphere, the mesosphere and the asthenosphere. The lithosphere is the upper part of the mantle. It is rigid and broken up into large pieces called plates. The mesosphere is the middle mantle and it has a silly putty texture. The asthenosphere is the lower mantle.

Outer Core: this is of a liquid state and temperatures are very high. Composed of nickel and iron.

Inner Core: this layer of the Earth is the inner most layer and is a very dense, solid ball made of nickel and iron.

Convection CurrentsIn the mantle, you have heat being cycled through convection currents. During this process, the magma that is in the mantle gets heated by the outer core and becomes less dense. As it gets heated it rises and then cools down. When the magma cools down, it then becomes denser and sinks down toward the outer core where it is reheated and the process happens all over again.

While the mantle heats up and cools down, it forms convection currents which cause the plates in the lithosphere above to move.

Plate Tectonics

The theory of plate tectonics: is the theory that Earth’s crust is broken into large plates that move towards, away, and slide past one another.

Theory of Continental Drift: states that the continents where once all together and over millions of years have separated. (this super continent was called Pangea)

Evidence to Support Continental Drift

1. Matching coastlines of Africa and South America 2. Common land mammal (cannot swim) fossils on different continents that are no longer connected3. Tropical plant life fossils on Antarctica

There are three main plate boundaries:

1. Convergent: this is where two plates collide into one another forming land features such as mountains, volcanoes, and trenches.

2. Divergent: this is where two plates move away from each other forming land features such as valleys, ridges.

3. Transform: this is where two plates slide past one another forming land features such as faults.

Transform Divergent Convergent

When two continental plates collide, crust gets folded and mountains are formed When two continental plates separate, a rift valley forms When an oceanic and a continental plate collide, the denser oceanic plate sinks beneath the continental

plate and a volcano is formed When two oceanic plates collide, a trench is formed When two oceanic plates separate, a mid-ocean ridge is formed

Subduction zone: when an oceanic plate and a continental plate collide, the oceanic plate which is denser will sink beneath the less dense continental plate.

In the diagram, you will see how plates move.

1. pointing out the two converging plates2. the convection currents in the mantle\3. is the hot magma rising 4. the magma is still rising 5. this is a divergent plate boundary6. A mid-ocean ridge is formed when the magma hits the ocean floor. Remember that the rocks closest to the

ridge are younger than the ones that are further away from the middle of the ridge.

10. Shows the subduction zone where the oceanic plate sinks beneath the continental plate.

REMEMBER THAT EARTHQUAKES AND VOLCANIC ACTIVITY ALWAYS OCCUR ALONG A PLATE BOUNDARY.

Rock Cycle

Types of Rocks

1. Sedimentary: formed when small pieces of rock are deposited at the bottom of lakes and rivers. The rocks will continue to be deposited and form multiple layers. Pressure will build up and the rocks will be compacted (squeezed together) and then the will harden (cementation) this is the only type of rock that contains fossils.

2. Metamorphic: formed when a rock is pulled back down into Earth’s interior where it gets heated and large amounts of heat and pressure squeeze and shape and the rock morphs into a metamorphic rock. This can only happen inside Earth’s interior.

3. Igneous: formed when magma or lava cools and hardens. There are two types of igneous rocks: extrusive: this rock is formed outside of Earth’s interior and has small crystals because it cools very fast. Intrusive: this rock is formed inside the Earth and has large crystals because it cools very slowly.

Forces that Shape the Earth

1. Weathering: The process by which rocks are broken down into small grains and soil. Weathering can happen through rainfall, ice formation, or the action of living things, such as algae and plant roots.

a. There are two types of weathering i. Mechanical: occurs when rock is physically changed. The rock gets smaller, but it stays

the same kind of rock. For example, (ice wedging) water sometimes gets into the tiny cracks in boulders. If that water freezes, it expands, opening the crack even more and eventually splitting the rock into pieces. In a stream, the moving water often knocks rocks against other rocks and sand. Over time, the rocks become smoother and smaller. This process is called abrasion. If you’ve ever rubbed a piece of wood with sand paper, you’ve seen abrasion in action.

ii. Chemical: the rock reacts with substances in the environment like oxygen, carbon dioxide, and water to produce new substances. For example, iron in rock can react with oxygen and water to form rust, making the rock reddish and crumbly.

2. Erosion: is the movement of weathered materials to new places. Water, wind, gravity, and glaciers (rivers of moving ice) all cause erosion. Have you visited or seen picture of the Grand Canyon is Arizona? Over millions of years, water, wind, heat and cold weathered the rock, which was ultimately carried away by the Colorado River.

*Hint: A way to remember the difference between weathering and erosion is that weathering is like a little brother making a mess and breaking things while erosion is big brother picking up behind him.

Human Impact on Earth

1. Deforestation: is the clearing of trees, transforming a forest into cleared land. * the clearing of trees for building, increases the amount of soil erosion because the tree roots are not covering the soil and it is now exposed to the wind and water.

2. Urbanization: is a word for becoming more like a city. When populations of people grow, the population of a place may spill over from city to nearby areas

3. Desertification: the process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agriculture.

4. Air and water pollution: occurs through the increased use of cars and also through the increase use of pesticides. When it rains, the water can carry pesticides into larger bodies of water increasing water pollution.

5. Global warming: a gradual increase in the overall temperature of the earth's atmosphere generally attributed to the greenhouse effect caused by increased levels of carbon dioxide, chlorofluorocarbons, and other pollutants.

6. Greenhouse Effect: the trapping of the sun's warmth in a planet's lower atmosphere due to the greater transparency of the atmosphere to visible radiation from the sun than to infrared radiation emitted from the planet's surface.

Fossils and Geologic Time

Fossils: A fossil is an impression, cast, original material or track of any animal or plant that is preserved in rock after the original organic material is transformed or removed.

Traces and preserved remains of ancient life found within rock layers

• Fossils show :

– Biodiversity (the different types of organisms that have lived throughout Earth’s history)

– How species have changed over time (Evolution)

– Correlation between rock layers from around the world (similarities and evidence for continental drift)

– Relative ages to particular strata (a way to give dates to how old the Earth is)

– Evidence for the geological time scale (a way to break Earth’s history into smaller sections based on the different life forms that lived, evolved, or became extinct)

A fossil may be:

• an original skeleton or shell;

• a mold or cast;

• material that has replaced the once living thing;

• traces such as footprints or worm tubes

What conditions promote fossilization?

• Rapid burial and/or lack of oxygen

• Hard body parts such as skeletal bones or exoskeletons

What are the fossil types?

• Body fossils – actual parts of an organism, unaltered or altered (bones, shells, leaf imprints)

• Trace fossils – evidence of life that is not a body fossil (tracks, burrows, casts)

What are the modes of fossil preservation for body fossils?

Unaltered

Original Material - original, unaltered material from the living organism unaltered bone or shell

Encrustations or entombments – material is trapped inside coating such as amber

Mummification - quickly dried material

Freezing – material is trapped inside ice and tissue is preserved

Tar Seeps - original remains are trapped in tar

Altered

Permineralization (petrification)– pores in tissue are filled by minerals

Replacement – replacement of tissue with minerals

Carbonization – tissue material is decomposed or reduced to a film of carbon

Trace fossils

• Mold – reproduction of the inside or outside surface of a living thing

• Cast – duplicate of the original organism; usually formed by replacement of inside of living thing

MOLD CAST

• Tracks – impressions of passage of living things

FOOTPRINTS

RELATIVE DATING & AGE

• Relative Dating: putting rocks and geological events in correct chronological order

• Relative Age: how old something is in comparison to something else

• HOW?

– Use of sedimentary rocks

– Use of fossils

– Study of strata

The Law of Superposition: States that the oldest rock layers are at the bottom and the youngest are at the top as long as the layers remain undisturbed.

Fossils that are found within the same rock layer are the same age.

INDEX FOSSIL

Fossil that defines and identifies geologic periods; often in only one layer of rock

• Easily recognizable

• Short-lived (found only in a few layers f (rock worldwide)

• Wide distribution (geographic range)

LAW OF HORIZONTALITY

Folds or inclines: layers must have been deformed after they were deposited.

LAW OF SUCCESSION

Fossils are found in a predictable sequenceFossils in rock B are older then fossils in rock A

RADIOACTIVE DATING

Fossils are given an exact age based on how much radioactive material is left within the fossil sample. It is also known as absolute dating.

• Radiometric dating uses decay of unstable isotopes.• Isotopes are atoms of an element that differ in their number of neutrons.

• A half-life is the amount of time it takes for half of the isotope to decay.

GEOLOGIC TIME SCALE

• A series of time intervals that divides Earth’s history. Each layer of rock represents specific interval of time Index fossils help determine specific period. Time periods divided by specific events like mass extinctions.

FOSSILS AND THE GEOLOGIC TIME SCALE BOTH SHOW HOW ORGANISMS HAVE CHANGED OVER TIME AND THIS IS ALSO WHAT SPLITS DIFFERENT PERIODS OF GEOLOGIC TIME.

Sample Questions

1. Deforestation occurs when large areas of trees are cut down. Which of the following impacts on the environment would result from deforestation?

A. increased erosion B. colder temperatures C. excess ground moisture D. greater oxygen production

2. The oldest rock formation identified on Earth is found on the shoreline of Hudson Bay in Canada. This rock formed 4.28 billion years ago. What information does a scientist need to more accurately determine the age of a rock?

A. the percentage of each mineral that makes up the rock B. the thickness of younger rock layers that cover the rock C. the amount of each radioactive element present in the rock D. the amount of weathering present on the surface of the rock

3. In which layer of Earth are the convection currents that directly result in tectonic plate motion found?

A. 1 B. 2 C. 3 D. 4