earths interior. geology : the study of planet earth geologists study the processes that create...

INSIDE EARTHCHAPTER 1: PLATE TECTONICS

Earths Interior

GEOLOGY

 Geology: the study of planet Earth

Geologists study the processes that create Earth’s features and search for clues about Earth’s history Geologists have to make predictions about what the

Earth’s interior is made of by making indirect observations of seismic waves

Forces beneath the Earth’s surface change the Earth’s appearance. There are two types of forces:

Constructive vs. Destructive Forces

Constructive: forces that build up mountains and landmasses

Destructive: forces that destroy mountains and other features of land

Continents Continents: the

seven great landmasses surrounded by oceans the seven

continents: 1. North America 2. South America 3. Africa 4. Europe 5. Asia 6. Australia 7. Antarctica

Geologists cannot observe Earth’s interior directly.

Use seismic waves: vibrations that travels through Earth, carrying the energy released during an earthquake

determine the speed and path of these waves to reveal the inner Earth’s structure

Earth is made up of 4 main layers

1. CRUSTCrust: Layer of rock that forms Earth’s

outer skin (made of Oxygen, Silicon, Aluminum, Calcium, Iron, Sodium, Potassium and Magnesium)

Includes soil and water 8-40 km thick

Oceanic Crust: crust beneath the ocean Thin layer of crustMade of- basalt: dark dense rock with a fine

texture Continental Crust: crust that forms the

continents Thicker layer of crustMade mainly of granite, which then

weathers and redeposits into many sedimentary and metamorphic rocks

2. MANTLE

Mantle: a layer of hot rock under the Earth’s crust (made of a material called peridotite which is high in iron and magnesium)

Lithosphere: a rigid layer made up of the uppermost part of the mantle and the crust; about 100km thick- (tectonic plates) Under the Lithosphere is a layer of hot rock Temperature and pressure in the mantle increase

with depth Asthenosphere: thick, soft material that

flows in the mantle; about 3,000km thick; moves in a convection current

CORE

Core: innermost layer of Earth; consists of 2 parts (made of iron and nickel)

3. Outer Corelayer of molten metal that surround the inner

coreBehaves like a thick liquidIs under enormous pressure

4. Inner CoreDense ball of solid metalExtreme pressure makes it a solid

Magnetic Field

The Earth has a magnetic field that is caused by the inner core spinning within the outer

What is this magnetic field called?

In perspective

The crust is a very thin layer compared to the others.

COOLING EARTH THEORYWe already know that over time, the Earth’s crust cooled. The crust is thin, relatively, varying from a few tens of kilometers thick beneath the continents to less than 10 km thick beneath the oceans.

The crust and upper mantle together constitute the lithosphere, which is typically 50-100 km thick and is broken into large plates. These plates sit on the asthenosphere. The asthenosphere is kept plastic largely through heat generated by radioactive decay. This heat source is relatively small, but nevertheless, because of the insulating properties of the Earth's rocks at the surface, this is sufficient to keep the asthenosphere plastic in consistency.

Heat Sources in the Earth

1. Heat from the early accretion and differentiation of the Earth

still slowly reaching surface

2. Heat released by the radioactive breakdown of unstable nuclides

Heat Transfer

1. Radiation

2. Conduction

3. Convection

What is Plate Tectonics?

If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.

Plate Tectonics

The Earth’s crust is divided into 12 major plates which are moved in various directions.

This plate motion causes them to collide, pull apart, or scrape against each other.

Each type of interaction causes a characteristic set of Earth structures or “tectonic” features.

The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.

World Plates

What lies beneath the tectonic plates?

Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.

Plate Movement

“Plates” of lithosphere are moved around by the underlying hot mantle convection cells

WHAT HAPPENS AT TECTONIC PLATE BOUNDARIES?

Divergent

Convergent

Transform

Three types of plate boundaries

Spreading ridges As plates move apart new material is

erupted to fill the gap

Divergent Boundaries

Age of Oceanic Crust

Courtesy of www.ngdc.noaa.gov

Iceland has a divergent plate boundary running through its middle

Iceland: An example of continental rifting

There are three styles of convergent plate boundaries Continent-continent collision Continent-oceanic crust collision Ocean-ocean collision

Convergent Boundaries

Forms mountains, e.g. European Alps, Himalayas

Continent-Continent Collision

Himalayas

Called SUBDUCTION

Continent-Oceanic Crust Collision

Oceanic lithosphere subducts underneath the continental lithosphere

Oceanic lithosphere heats and dehydrates as it subsides

The melt rises forming volcanism

E.g. The Andes

Subduction

When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.

The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.

The worlds deepest parts of the ocean are found along trenches. E.g. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate Collision

Where plates slide past each other

Transform Boundaries

Above: View of the San Andreas transform fault