Plate Tectonics

Exploring Inside the Earth Geologists have used evidence from rock samples and evidence from seismic waves to learn about Earth’s interior. Geologists are scientists who study the forces that make and shape planet Earth. Geology is the study of planet Earth.

Studying Surface Changes Constructive forces shape the surface by building up mountains. Destructive forces are those that slowly wear away mountains and, eventually, every other feature on the surface.

The Crust Three main layers make up Earth’s interior: the crust, the mantle, and the core. Each layer has its own conditions and materials. The crust is a layer of solid rock that includes both dry land and the ocean floor.

The Mantle Earth’s mantle is made up of rock that is very hot, but solid. The mantle is divided into layers based on the physical characteristics of those layers.

The Core The core is made mostly of the metals iron and nickel. It consists of two parts–a liquid outer core and a solid inner core.

Types of Heat Transfer There are three types of heat transfer: radiation, conduction, and convection. Radiation – the transfer of energy through empty space Heat transfer – the movement of energy from a warmer object to a cooler object Conduction – heat transfer by direct contact of particles of matter

Convection Currents Heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion. Convection currents – the flow that transfers heat within a fluid Convection – heat transfer by the movement of a heated fluid

Convection Currents in Earth Heat from the core and the mantle causes convection currents in the mantle. This is how the heat is transferred.

Continental Drift Wegener’s hypothesis was that all the continents were once joined together in a single landmass. Continental drift – The idea that the continents slowly moved over Earth’s surface.

Scientists now believe that about 250 million years ago, a super-continent known as Pangaea existed. This super-continent was made up of all the continents on Earth.

Evidence for Continental Drift Fossils – any trace of an ancient organism that has been preserved in rock. Wegener could not provide a satisfactory explanation for the force that pushes or pulls the continents.

Mid-Ocean Ridges The East Pacific Rise is just one of the many mid-ocean ridges that wind beneath Earth’s oceans. Sonar – a device that bounces sound waves off under-water objects and then records the echoes of these sound waves The mid-ocean ridge is the longest chain of mountains in the world

What Is Sea-Floor Spreading? In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added to the ocean floor. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

Evidence for Sea-Floor Spreading Several types of evidence supported the theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

Subduction at Trenches In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle through deep-ocean trenches. Deep-ocean trenches are deep underwater canyons formed where the oceanic crust bends downward. Subduction – the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Growing an Ocean Because of sea-floor spreading, the distance between Europe and North America is increasing by a few centimeters per year.

How Plates Move The lithosphere is broken into separate sections called plates. The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates. Faults – breaks in Earth’s crust where rocks have slipped past each other Scientific theory – a well-tested concept that explains a wide range of observations

Plate Boundaries There are three kinds of plate boundaries: divergent boundaries - convergent boundaries transform boundaries. A different type of plate movement occurs along each type of boundary. Rift valley – a deep valley that forms along the divergent boundary

Plate Boundaries At the locations where two tectonic plates interact, a boundary between these plates exist. There are three types of boundaries that geologist observe. These boundaries are divergent boundaries, convergent boundaries, and transform boundaries.

Continental Drift It has taken the continents about 225 million years since the breakup of Pangaea to move to their present locations.

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