Chapter 11Earth’s Structure

By Spencer Smith, Valerio Rosales, and Reny Gonzales

Characteristics of Minerals

• A mineral is a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition.

• The reaping pattern of a mineral’s particles forms a solid called a crystal.

Identifying Minerals

A streak test can be used to help tell apart minerals. The streak of a mineral is the color of its powder.

Checking a mineral’s luster, or how well light reflects off of it, is another way to categorize them.

Streak Luster

Identifying Minerals

Mohs hardness scale ranks ten minerals from softest to hardest.

If it splits easily along flat surfaces then it has a property called cleavage. Most minerals do not split apart evenly. Instead

they have a characteristic type of fracture, which describes how a mineral looks when it breaks apart in an irregular

way.

Cleavage

Fracture

Mineral Formation• Minerals can form as hot magma cools inside the

crust, or as lava hardens on the surface of the crust.

• Crystallization is only one of the ways minerals form.

• Minerals can change depending on temperature and pressure to form new minerals.

Gold Crystallization

Cooling Magma

Rock Classification and the Rock Cycle

Rock Classification

• When identifying a rock sample, geologists observe the rock’s mineral composition, color and texture.

• Granite is generally a light-colored rock that has high silica content.

• Basalt is a dark-colored rock that is low in silica content.

BasaltGranite

Rock Classification

• Igneous rock forms from the cooling of molten rock.• Sedimentary rock forms when particles of other rocks

or the remains of plants and animals are compressed and cemented together.

• Metamorphic rock forms when an existing rock is changed by intense heat and pressure and/or chemical reactions.

Igneous Rock Sedimentary Rock Metamorphic Rock

The Rock Cycle

The rock cycle is a series of processes on Earth’s

surface and in the crust/mantle that slowly change rocks from one

kind to another.

Earth’s Interior Structure

• The crust - thin, rocky outer layer of earth; is divided into oceanic and continental portions.

• Over 82% of the Earth’s volume is contained in the mantle - a solid, rocky shell that extends to a depth of 2890 km.

Earth’s Interior Structure

• The outer core is a liquid 2260 km thick. The flow of metallic iron within this zone generates Earth’s magnetic field.

• The inner core is a sphere having a radius of 1220 km. It’s solid because of the immense pressure.

Earth’s Interior Structure

• The crust and uppermost mantle forms a relatively cool, rigid shell called the lithosphere.

• Beneath the lithosphere lies a soft, comparatively weak layer known as the asthenosphere.

Plate Tectonics

Pangaea

Plate Tectonics

Continental Drift

In 1911, a young German scientist named Alfred Wegner came up with the continental drift theory in order to explain how identical fossils could be found on both

coasts of the Atlantic, and how the different continents could be combined like puzzle pieces

(Pangaea).

The Theory of Plate Tectonics

Plate tectonics is the geological theory that states that pieces of Earth’s lithosphere

are in constant, slow motion, driven by

convection currents in the mantle.

The Theory of Plate Tectonics• A transform boundary is a place where two plates slip past each other,

moving in opposite directions. Earthquakes occur frequently along these boundaries.

• The place where two plates move apart, or diverge, is called a divergent boundary. A deep valley, called a rift valley, forms along divergent boundaries.

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

Seafloor Spreading

At a mid-ocean ridge, molten material rises from the mantle and erupts. The molten

material then spreads out, pushing older rock to both sides of the ridge.

Earthquakes and Volcanoes

The Formations of Faults• Most faults occur along boundaries, where the forces of plate

motion push or pull the crust so much that the crust breaks.• There are three main types of faults: normal faults, reverse faults,

and strike-slip faults.• Tension causes normal faults, compression causes reverse faults

and shearing causes strike-slip faults.

Earthquakes and Seismic Waves

• An earthquake is the shaking and trembling that results from the formation of faults or movements of rocks along faults. The point of origin is called the focus. The point on the surface above the focus is the epicenter.

Earthquakes and Seismic Waves• P waves compress and expand the ground like an accordion.• S waves vibrate from side to side and up and down.• Surface waves are what’s left of P and S waves when they reach

the surface.• A tsunami is a giant ocean wave caused by an underwater

earthquake.

Seismograph showing the seismic waves during the 2005 tsunami in Indonesia.

Volcanoes and Plate Tectonics• A volcano is a weak spot

in the crust where molten material, or magma, comes to the surface.

• A hot spot is an area where material from within the mantle rises and then melts, forming magma.

• Inside a volcano, magma collects in a pocket called a magma chamber.

• The magma leaves this chamber through a vent.

Volcanoes and Plate Tectonics• A pyroclastic flow occurs when an explosive eruption hurls out ash, cinders, and

bombs.There are 3 types of volcanoes:

• Shield Volcano - produced by quiet volcanic eruptions; shaped like wide, gently sloping mountains.

• Cinder Cone Volcano - produced by explosive volcanic eruptions; steep, cone-shaped hills or mountains.

• Composite Volcano - produced by a mixture of quiet and explosive eruptions; wide, moderately-sloped, cone-shaped mountains.

Cinder Cone Volcano Composite VolcanoShield Volcano