World’southward Tectonic Plates
The world’s chaff is broken into separate pieces chosen
(Fig. vii.xiv). Recall that the crust is the solid, rocky, outer beat of the planet. It is composed of two distinctly unlike types of cloth: the less-dense continental crust and the more-dumbo oceanic crust. Both types of crust balance atop solid, upper drapery material. The upper curtain, in plough, floats on a denser layer of lower mantle that is much similar thick molten tar.
Each tectonic plate is free-floating and tin can move independently. Earthquakes and volcanoes are the directly result of the movement of tectonic plates at fault lines. The term
error is used to describe the boundary between tectonic plates. Most of the earthquakes and volcanoes around the Pacific ocean bowl—a pattern known as the “ring of fire”—are due to the movement of tectonic plates in this region. Other observable results of short-term plate motion include the gradual widening of the Great Rift lakes in eastern Africa and the rising of the Himalayan Mountain range. The motion of plates tin be described in four full general patterns:
Globe’southward solid crust acts equally a heat insulator for the hot interior of the planet.
is the molten stone below the crust, in the drape. Tremendous heat and pressure within the earth crusade the hot magma to menstruation in convection currents. These currents cause the motility of the tectonic plates that make up the earth’southward crust.
Activity: Modeling Plate Spreading
Simulate tectonic plate spreading by modeling convection currents that occur in the mantle.
Activity: Earth’south Plates
Examine a map of the earth’s tectonic plates. Based on prove that has been institute at plate boundaries, make some hypotheses nigh the movement of those plates.
The earth has changed in many ways since it first formed 4.v billion years ago. The locations of Earth’s major landmasses today are very different from their locations in the past (Fig. 7.eighteen). They have gradually moved over the course of hundreds of millions of years—alternately combining into supercontinents and pulling apart in a process known every bit
continental drift. The supercontinent of Pangaea formed every bit the landmasses gradually combined roughly between 300 and 100 mya. The planet’s landmasses somewhen moved to their current positions and will continue to motion into the time to come.
is the scientific theory explaining the movement of the earth’s crust. It is widely accepted by scientists today. Recall that both continental landmasses and the ocean floor are part of the earth’s chaff, and that the crust is broken into private pieces called tectonic plates (Fig. 7.14). The movement of these tectonic plates is likely caused by convection currents in the molten rock in Earth’southward mantle beneath the crust. Earthquakes and volcanoes are the short-term results of this tectonic movement. The long-term consequence of plate tectonics is the movement of unabridged continents over millions of years (Fig. 7.eighteen). The presence of the same type of fossils on continents that are now widely separated is evidence that continents have moved over geological history.
Action: Continental Movement over Long Time Scales
Evaluate and interpret several lines of evidence for continental migrate over geological time scales.
Evidence for the Movement of Continents
Testify for continental drift is likewise establish in the types of rocks on continents. There are belts of rock in Africa and South America that lucifer when the ends of the continents are joined. Mountains of comparable age and construction are institute in the northeastern part of North America (Appalachian Mountains) and across the British Isles into Norway (Caledonian Mountains). These landmasses can exist reassembled so that the mountains class a continuous concatenation.
= long term temperature and weather patterns) written report evidence of prehistoric climates. Testify from glacial striations in rocks, the deep grooves in the land left by the movement of glaciers, shows that 300 mya there were large sheets of ice covering parts of Southward America, Africa, India, and Commonwealth of australia. These striations signal that the management of glacial movement in Africa was toward the Atlantic ocean basin and in South America was from the Atlantic sea basin. This evidence suggests that South America and Africa were in one case connected, and that glaciers moved across Africa and South America. There is no glacial testify for continental move in Due north America, because there was no water ice covering the continent 300 meg years agone. Due north America may have been nearer the equator where warm temperatures prevented ice sheet formation.
Seafloor Spreading at Mid-Sea Ridges
Convection currents bulldoze the movement of World’s rigid tectonic plates in the planet’s fluid molten mantle. In places where convection currents rise up towards the crust’s surface, tectonic plates move away from each other in a process known as
(Fig. 7.21). Hot magma rises to the crust’southward surface, cracks develop in the body of water floor, and the magma pushes up and out to form mid-sea ridges.
or spreading centers are fault lines where two tectonic plates are moving away from each other.
Mid-ocean ridges are the largest continuous geological features on Earth. They are tens of thousands of kilometers long, running through and connecting near of the ocean basins. Oceanographic data reveal that seafloor spreading is slowly widening the Atlantic ocean basin, the Ruby Ocean, and the Gulf of California (Fig. 7.22).
Image by Byron Inouye
Some shield volcanoes, such every bit the islands in the Hawaiian archipelago, began forming on the ocean floor over a hot spot. Each shield volcano grows slowly with repeated eruptions until it reaches the surface of the water to form an island (Fig. 7.25). The highest peak on the island of Hawai‘i reaches iv.2 km higher up bounding main level. However, the base of operations of this volcanic island lies about 7 km below the water surface, making Hawai‘i’s peaks some of the tallest mountains on Earth—much higher than Mount Everest. About all of the mid-Pacific and mid-Atlantic ocean basin islands formed in a similar fashion over volcanic hot spots. Over millions of years as the tectonic plate moves, a volcano that was over the hot spot moves away, ceases to erupt, and becomes extinct (Fig. vii.25). Erosion and subsidence (sinking of the earth’southward crust) eventually causes older islands to sink beneath ocean level. Islands tin erode through natural processes such as wind and h2o flow. Reefs continue to grow around the eroded land mass and form fringing reefs, equally seen on Kauaʻi in the principal Hawaiian Islands (Fig. 7.26).
Eventually all that remains of the isle is a band of coral reef. An
is a band-shaped coral reef or group of coral islets that has grown around the rim of an extinct submerged volcano forming a primal lagoon (Fig. 7.27). Atoll formation is dependent on erosion of land and growth of coral reefs around the isle. Coral reef atolls can but occur in tropical regions that are optimal for coral growth. The main Hawaiian Islands will all likely go coral atolls millions of years into the future. The older Northwestern Hawaiian Islands, many of which are at present atolls, were formed by the same volcanic hot spot as the younger master Hawaiian Islands.
The Force That Drives Earthquake Activity is _____