EARTH Unit 3

Earth's Origin Lesson 1 While it was still in the molten state, separation of elements occurred within the earth. light inert gasses like Helium (He) and Krypton (Kr) were lost to outer space. heavy elements like Nickel (Ni) and Iron (Fe) sunk toward the center.

Earth's Origin Several concentric shells were formed in and around the earth, each one enriched in certain elements. Atmosphere Molten crust Mantle Core

Earth's Origin As the earth cooled, a solid crust of silicate rocks formed more than 4 billion years ago. This sealed the hot magma inside. Atmosphere and oceans Solid crust Mantle Core

Earth's Origin Local fractures in the solid but relatively thin crust, led to extensive volcanism. Atmosphere and oceans Solid crust Mantle Core

Earth Structure Earth is a heat engine. Heat is a form of energy. An engine converts energy from one form into another to perform work. Earth is constantly at work.

Earth Structure Two major sources of energy drive earth processes: internal heat solar heat

Earth Structure Internal heat drives: volcanism Plate tectonics mountain building

Earth Structure Solar heat drives processes near the surface such as: life erosion water cycle cars (fossil fuels) waves

Earth Structure The internal source of heat is revealed by the geothermal gradient. (the progressive increase in temperature with depth). High geothermal gradients (~ 60 degrees/km) are typical of volcanic areas. Low geothermal gradients (~ 10 degrees/km) are found in areas of thick, stable continental crust.

Earth Structure Low geothermal gradients (~ 10 degrees/km) are found in areas of thick, stable continental crust.

Earth Structure Internal heat sources are related to: primordial heat radiogenic heat

Earth Structure Distribution of internal heat tends to become uniform through redistribution.

Earth Structure Redistribution of heat is achieved through: Conduction Convection

Earth Structure The most impressive work done by "Earth's Heat Engine" is associated with convection.

Earth Structure Convection is responsible for: Plate movement (plate tectonics) volcanism mountain building

Earth Structure The Atlantic Ocean began forming almost 200 million years ago. It is still enlarging.

NEXT LESSON INTERNAL STRUCTURE and Seismology

INTERNAL STRUCTURE and Seismology Unit 3 Lesson 2 The seismic tool is used to determine the thickness of each of the earth's internal shells.

INTERNAL STRUCTURE and Seismology The earth's crust is: thin (5-20 km) under oceans thick (25-40 km) under continents separated from the mantle by the Mohorovicic discontinuity (MOHO)

INTERNAL STRUCTURE and Seismology

The mantle behaves as a : fluid when energy input is slow (i.e. plate motion) solid when energy input is rapid (i.e. seismic waves)

INTERNAL STRUCTURE and Seismology

SEISMOLOGY The very deep internal structure and composition of the Earth, below the depth to which a well can be drilled, can be surmised from studies of: stressed materials meteorites lab experiments

SEISMOLOGY Seismology is a tool for mapping subsurface layers. It measures the travel time of energy waves within the earth.

SEISMOLOGY When the energy waves encounter a change in rock density, refraction and reflection occur. Some of the energy is bounced back to the surface (reflection) and some continues downward at a new and different speed and direction (refraction).

SEISMOLOGY Seismic energy can be transmitted as different waves: P pressure or primary waves S shear or swing waves

SEISMOLOGY P-waves vibrate in the same direction as the wave travels. They are sometimes called primary waves because they travel fast and arrive at the recording station before S-waves. They can be transmitted through both liquids and solids.

SEISMOLOGY S-waves, sometimes called shear waves, vibrate perpendicular to the direction of travel. They do not transmit through fluids.

SEISMOLOGY S-waves are lost deep within the earth at the boundary between the mantle and the outer core. This indicates that the outer core is liquid.

SEISMOLOGY Abrupt variations in the velocity of seismic waves mark boundaries (discontinuities) within the earth. These indicate outer margins of the earth's internal shells (i.e. mantle, outer core)

NEXT LESSON Plate Tectonics

Plate Tectonics Unit 3 Lesson 4 CRUSTAL PLATES

Plate Tectonics Atlantic Islands are relatively young near the Mid- Atlantic Ridge (Iceland is about 25 million years old and still growing). older toward the margins of the ocean (Canary's are more than 100 million years old).

Plate Tectonics As new crust is formed, iron-rich minerals in the volcanic lava become aligned with the earth's magnetic field, recording paleomagnetic reversals.

Plate Tectonics The Earth's magnetic field has reversed many times

Plate Tectonics Symmetrical magnetic bands on either side of the Mid-Atlantic ridge indicate: similar magnetism similar age ocean spreading

Plate Tectonics Seven major Tectonic plates have been identified along with many smaller ones.

Plate Tectonics PLATE MARGINS are the location of most: faults earthquakes volcanoes

Plate Tectonics Earth has a finite surface area, so as new material is added to the crust, the same amount of material must be consumed elsewhere.

Plate Tectonics RIFTING occurs and new material is added to the crust where the plates diverge. The diagram shows rifting at the Mid-Atlantic Ridge but it also happens in other places, for instance the East African rift.

Plate Tectonics Ocean crust and continental crust material is consumed in Subduction Zones. These are places where heavier oceanic crust slides beneath lighter rocks of the continental crust. A good example of this is along the west coast of South America beneath the Andes.

Plate Tectonics Different types of rocks form in different parts of the Earth's crust. The diagram shows how this relates to the "rock cycle".

Plate Tectonics Large deposits of minerals and fossil fuels form at the margins of Tectonic Plates

Plate Tectonics Tectonic plates change both in position and direction of movement through time. (note: the northward drifting of India)

Unit 4 Minerals and Rocks