All about our Earth

Layers of the Earth• Scientist think that as the Earth was

forming the denser materials, such as iron and nickel, sank to the center due gravity and the increase in temperature. The less dense material moved toward the surface and all the other material settled between the surface and the center.

•The layers of the Earth are crust, mantle, inner core and outer core.

Crust• There are two types of crust:

Continental (where we live) and Oceanic (under the ocean).

• The crust is the least dense, thinnest and coolest layer of rock.

• The boundary between the crust and the next layer, the mantle, is called the Moho.

Lithosphere• The lithosphere layer includes

the crust and the upper mantle. It is hard and rigid and makes up the tectonic plates. The tectonic plates float on the mantle and constantly move.

Mantle• The mantle is made of two parts the

asthenosphere and the mesosphere. The thickest layer of about 67% of Earth’s mass. It is made of molten rock with the temperature between 870°C - 4400°C. The part of the mantle closest to the core becomes hotter causing a convection current throughout the liquid. Convection current is when hot liquid rises (less dense) and cool liquid sinks (denser). This movement causes the plates to move.

Core The core is made of two parts – the Inner Core and the Outer Core

Inner Core• More Dense• Temperature 7000°C –

8000°C• Solid• Mostly made of iron and little

nickel

Outer Core• Less dense than inner core• Temperature 4400°C –

6100°C• Liquid• Made of both iron and

nickel

•C – Crust•L- Lithoshpere•A – Asthenosphere•M – Mesosphere•O – Outer Core• I – Inner Core

The Difference between the two types of Crust

• There are two types of lithospheric crust – oceanic and continental. Continental has a average thickness of 30 km. Continental crust is mostly made of granite. Oceanic crust has a thickness of 5-8 km thick. The composition of oceanic crust is basalt.

• The lithospheric crust are made up of tectonic plates which float on the asthenosphere layer of soft, hot rock. The hot, soft rock rises, cools, and sinks, then is heated and rises again. This is called convection currents.

• There are two proposed motions that can take place: slab pull and ridge push.– Slab pull occurs where gravity pulls the edge

of cool dense place into the asthenosphere because the plates are ridged; the entire plate is pulled along. (Located at subduction zones)

– Ridge push occurs when material from the mid-ocean ridge slides downhill from the ridge. The material pushes the rest of the plates. (Located where plates are separating)

Pangaea

• Pangaea (Pangaea) – In early geologic time a super continent existed that incorporated almost all the Earth’s land masses.

• Pangaea covered almost 1/3 of Earth’s surfaces. Pangaea (all lands) was surrounded by a global ocean called “panthalassa” (all seas).

• Pangaea was fully assembled 270 million years ago and began to break up 200 million years ago.

• The idea of Pangaea was proposed by Alfred Wegener in 1912 as part of his continental drift theory.

Continental Plates

• Shortly after the earth was formed the crust broke up into huge thick plates that drift on the mantle. The plates are made of rock and drift all over the globe – they move both horizontally (sideways) and vertically (up and down). Over long periods of time, the plates also change in size as their margins are added to, crushed together or pushed back into earth’s mantle.

• The Pacific Ring of Fire is mainly made up of the plate boundaries that border the Pacific Ocean basin. The pacific ring of fire is a region of high earthquake and volcanic activity that surrounds the majority of the Pacific Ocean Basin.

Continental Drift• Continental drift is the theory that the continents have moved. Alfred

Wegener was a German scientist that proposed the idea of continental drift. Wegener based his theory on fossil evidence, climate change evidence and geological evidence.

• Fossils – Ancient reptile fossils of the mesosaursus were discovered in South America and West Africa – but nowhere else in the world. This is evidence that these two land masses were joined.

• Climate – Greenland today lies near the arctic circle yet fossils of tropical plants lie near its shores – evidence that Greenland was once somewhere else.

• Geology – the type of rock found in Brazil matched that of rock in Western Africa. Limestone layers in the Appalachian mountains of North America were exactly like the limestone in Scotland’s Highlands.

• No one believed Wegener because he couldn’t find a way to make the continents move. Plate tectonics is the theory that explains continental drift.

Convergent Boundaries• A plate boundary is where two continental plates are next to each other. Like the

boundary between Georgia and South Carolina. What the plates do determines the type of boundary that exists. There are three types of boundaries, convergent, divergent and transformation.

• When two plates move toward each other and collide – this is a convergent plate boundary. What happens when two plates collide depends on the type of plates.

• Oceanic & Continental Convergence• When continental and oceanic plates collide something called “subduction” occurs.

The oceanic plate sinks under the continental plate because the oceanic plate is denser. The oceanic crust sinks back into Earth’s mantle where it melts because of the intense heat & friction. This collision causes cracks in plates. The magma rises up the cracks creating volcanoes. The subduction also causes deep ocean trenches.

• Continental & Continental Convergence• When two continental plates collide one plate goes slightly under the other but

subduction does not occur because the density of the plates is almost the same. The pressing together of two plates pushes both plates up and the crust folds. Fold Mountains are formed at these boundaries.

• Oceanic & Oceanic Convergence

Deforming the Earth’s Crust

• Plate interactions cause Faults• Faults are fractures, or breaks, in earth’s

lithosphere, along which blocks of rock move past each other.

• Reverse Faults – Along a reverse fault the block of rock above the fault plane moves up relative to the other block. This occurs at convergent boundaries.

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Divergent Boundaries• New crust is created as two or more plates pull apart – this is called a

divergent boundary. A divergent boundary is considered constructive because new crust is made.

• Divergent boundaries are located at the boundary of oceanic plates or at the boundary of continental plates. The mid-ocean ridge in the ocean is an example of a divergent boundary. At the mid-ocean ridge the plates move away from each other and the magma comes up from the mantle where it is cooled by the ocean water and creates new crust.

• In Africa there is a divergent boundary where two continental plates pull away from each creating the Great Rift Valley.

• Normal Faults – Along a normal fault the block of rock above the fault planes slides down relative to the other block. Earth quakes along normal faults are common near divergent boundaries.

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• Sea Floor Spreading - When the sea floor was mapped in the 1950’s scientists found that the ocean floor wasn’t smooth but instead had a mid-ocean ridge – which are large mountains rising from the ocean floor. These mid-ocean ridges were created by sea floor spreading.

• As the tectonic plates that make up the ocean floor move away from each other hot magma from the Earth’s mantle bubble up. The magma is cooled by sea water. The new rock forms a new part of the Earth’s crust. Over time new oceanic crust pushes older crust farther away.

• Age of the Sea Floor- The age of the continental crust is about 4.6 billion years old – whereas the age of the sea floor is much younger. The sea floor is constantly being renewed and destroyed. The newest ocean floor is being created all the time. The oldest sea floor is about 160 million years old. Ocean trenches are long narrow depressions in the sea floor along convergent plate boundaries. At this place on the plate (the denser plate) moves under another plate where it melts and is destroyed.

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Transform Boundaries

• A transform plate boundary is one where two plates slide laterally past each other. However, movement is not smooth because of friction between the rocks of the two plates. Therefore, sometimes two plates would get stuck and lock together. But since the convection currents of the underlying magma are still dragging the plates, much tension and pressure is built up at the transform boundary. When there is enough built up pressure, rocks in the plates break and are jerked apart – resulting in an earth quake.

• A transform boundary creates a strike-slip fault – along a strike slip fault the rock moves sideways on either side of the fault plane. These types of faults occur at transformation boundaries.

Types of Mountains

Volcanoes

Earthquakes

Minerals are all around us.

• Minerals have four characteristicso Formed in nature o They are solids o Have a definite chemical makeup.

Minerals are always made up of the same materials in the same proportions.

o Have a crystal structure. crystal are solid with the atoms arranged in an orderly,

repeating, three-dimensional pattern. Crystal structures can determine a mineral's properties,

and not all minerals have the same crystal structure.

Scientists classify minerals into groups based on their chemical makeup.

oSilicates and Non-silicate (most common) making up 90 percent of the rocks in Earth's

crust. They contain oxygen and silicon bonded together. Common silicates are quartz, feldspar, and mica.

oCarbonates (second most common)They oxygen and carbon bonded together. A common carbonate is calcite.

oOxides are important minerals. Metals are refined from oxides for human use. They contain a metallic element bonded to

oxygen. A common oxide is hematite, a source of iron.

A mineral is identified by its properties

•A mineral's appearance helps identify it.Color - they can be almost any color, but most have a limited color range. Because different minerals can be the same color, this is not the best method to identify them.

•Streak - the color of the powder left behind when a mineral is scraped across a surface. Streak is a better clue to a mineral's identity than surface color is.

• Luster - way in which light reflects from a mineral's surface.o Two major types of luster: Metallic and Nonmetallic.o The luster can dull if exposed to the atmosphere or to water, but if the mineral is broken to reveal a fresh surface, the characteristic luster can be seen.

The way a mineral breaks helps identify it.

oCleavage - tendency of a mineral to break along flat surfaces. the bonds of atoms in the crystal structure are

weaker in one or more directions. These are the directions in which the mineral tends to break.

oFracture - tendency of a mineral to break into irregular pieces. the bonds that join the atoms are fairly equal

in strength in all directions. The mineral breaks into different shapes, not along flat surfaces.

Density and Hardness help identify Minerals.• Density - the amount of mass per unit volume.

o Density can be very helpful in identifying minerals, including some that look alike.

o Example, gold and pyrite, as gold is much more dense than pyrite.

• Hardness - a mineral's resistance to being scratched. o It is determined by its crystal structure and the strength of its

bonds. Harder minerals have stronger bonds.

o The Mohs scale is often used to describe a mineral's hardness. Talc is the softest and diamond is the hardest. Minerals higher on the scale can scratch minerals lower

on the scale.

Some minerals have special properties.oCarbonates react with acid and form bubbles

of carbon dioxide. oFluorite and other minerals fluoresce, or glow

when exposed to ultraviolet light. oMagnetite and other magnetic minerals

attract a loosely held magnet. oSome minerals are radioactive.

Mohs Hardness ScaleHardness Mineral Associations and Uses

1 Talc Talcum Powder

2 Gypsum Plaster of Paris, Formed when seaweed evaporates

3 Calcite Limestone, Found in most shells

4 Fluorite Prevents Tooth Decay

5 Apatite Hungry! You must have a big “appetite”

6 Orthoclase Is a Feldspar

7 Quartz Watches and Computer Chips

8 Topaz November Birthstone

9 Corundum Sapphire and Ruby

10 Diamond A cutting Tool

Hardness of Some Items

2.5 Fingernail

2.5-3 Gold, Silver

3 Copper Penny

4-4.5 Platinum

4-5 Iron

5.5 Knife Blade

6-7 Glass

6.5 Iron Pyrite

7+ Hardened Steel File

2.3 Minerals are valuable resources. Minerals have many uses in industry and the

arts.oHematite and chromites are minerals from

which people obtain metals. Quartz, another mineral, is used to make glass and silicon computer chips.

oMica and talc are minerals used in paints. Certain minerals known as gemstones are used to make jewelry. Amethyst, diamond, and emerald are examples of gemstones. Metals such as silver and gold are also used in jewelry making and other decorative arts.

Minerals form in many ways.oAs water evaporates, elements from substances

dissolved in water can join to form mineral crystals.

oAs hot water cools, minerals dissolved in the water separate from the water and become solid again.

oAs molten rock cools, atoms join together to form different minerals.

oHeat and pressure within Earth cause new minerals to form as bonds between atoms break and join again in new ways.

oA few minerals are produced by living things. For example, some ocean animals produce carbonate minerals to form shells.

Minerals must be removed from the ground, or mined, before they can be used to make products. Mining occurs close to Earth's surface, as well as deep underground. Miners recover ores, which are rocks that contain enough of a valuable mineral to be mined for a profit.

oSurface mining recovers minerals at or near Earth's surface. Examples of surface mines are strip mines and open-pit mines.

oDeep mining recovers minerals far below Earth's surface. Deep mine tunnels can be horizontal or vertical, depending on where the ore is located.