Continental Drift (1980)

[Music] our Restless Earth a planet of continuing change the Earth surface has not always looked the same nor will it in the future geologists have tried to find the many reasons for these changes in the Earth's surface of appearance a theory called plate tectonics has given us a different view of the planet on which we live this concept is based on observations of the Earth's surface and on evidence which suggest that zones of rock within the Earth being very hot behave like a fluid this lava pool acts as a model of the Earth's surface slabs of solidified lava right on top of rising convection currents scientists now believe that huge slabs called plates make up Earth's outer zone and behave much the same way the theory of plate tectonics deals with the formation destruction and continued motion of these great segments of the Earth's crust when we plot earthquake and volcanic activity on a world map a pattern emerges the pattern shows that this activity is concentrated along certain zones these zones make up the boundaries of the Earth's major plates geologists think that at one time over 200 million years ago all major continents were joined this probable supercontinent is called angia here we see how Pangia may have broken apart and the continents drifted away from each other the continents appear to have changed position many times throughout Earth's long history continental drift is a process that continues even today evidence of this drifting can be seen when we examine the classical match of the coast lines of Africa and South America the continents nearly fit together like pieces of a jigsaw puzzle a compilation of computer calculations was made on the preciseness of this fit using information gathered both on land and at Sea the improved fit of the continents is made not by matching their edges at sea level but at the outer edge of the continental shelf the startling match of rocks and door deposits of similar type and geological age across this fit adds support to the theory the common ancestry of many forms of life such as an eating mammals found in Africa and South America provides further evidence that these continents were joined to understand plate tectonics we must go to different parts of the world to find evidence of plate movement this evidence is best seen along plate boundaries such as those associated with Iceland in 1963 an underwater eruption occurred just south of Iceland out at the ocean lava spewed forth molten rck kept rising from the ocean floor spreading out in all directions tremendous forces push this lava through fractures in the Earth's crust to form a new island cery this volcano Rose rapidly from the ocean floor then on haay a nearby Island another volcano erupted at 1973 lava poured from a rift or large crack which appeared in the flank of one of the older volcanic cones creating a new volcano why did this new volcano occur here off the coast of Iceland Iceland formed from the Atlantic ocean floor as lava welled upward along a great rift this Rift appears in the crest of a prominent feature extending along the Atlantic and known as the Mid-Atlantic Ridge the r drift in this ridge forms one kind of plate margin here plates are moving apart as new ocean floor is being formed a zone of rifting along the Mid-Atlantic Ridge Crest bisects Iceland from the islands of CTI and he the rifting can be traced onto the main island Iceland is a country of Fire and Ice Rising above the glaciers on the main island this chain of volcanic cones forms a black line that can be seen disappearing beneath the ice we can follow this evidence across the glaciers deep Fishers stretch across the land where the island is splitting apart at the rate of 2 to 5 cm a year looking across the Valley we can see more evidence of this sporadic movement newly formed lakes and long prominent fissures as Iceland splits apart due to the movement of the plates lava continues to flow upward enlarging the island in this artist conception we see the Mid-Atlantic Ridge and the two plates that are moving apart in this examp exaggerated cutaway we see two plates consisting of the crust and uppermost metal together they are called the lithosphere which ranges from 70 to 150 km in thickness the relatively thin lithosphere lies above a thicker Zone called the aerosphere this hotter Earth material provides a zone of flow over which the plates of the lithosphere move our knowledge of the Mid-Atlantic Bridge is based on data collected aboard research ships that have traversed the Atlantic Ocean in order to map the ocean bottom sonar waves are transmitted to the seafloor these waves are then reflected back from the irregular surface at slightly different time intervals the differences in arrival time of the Waves provide information used to make a scale diagram of the ocean bottom this map emphasizes the great irregularity and mountainous character of this part of the sea floor the Mid-Atlantic Ridge has numerous deep Rifts and prominent valleys it forms a broad and winding mountain range extending the length of the Atlantic nearly along the middle of the ocean from north to south this Ridge is part of a series of underwater mountains more than 64,000 km long that extend throughout the world oceans it is larger and longer than any system of mountain ranges on land along the western coast of South America a second kind of plate boundary exists here two plates are colliding this Collision causes one plate to plunge beneath the other creating a subduction zone as the descending plate plunges deeper and becomes hotter it gradually is absorbed into the aeno osphere movement along the descending plate may cause earthquakes and form localized zones of magma some of this magma rises along fractures to form volcanic mountains such as those found in the Andes earthquakes are also generated along still a third kind of plate boundary where one plate slides past another the coast of California is a prime example in this view of Southern California we can trace a zone of fractures commonly known as the San Andreas fault the Pacific Plate on the left is slipping past the North American Plate on the right this kind of plate boundary is called a transform fault dominant features of the San Andreas fall can be seen on California's cizo plane this segment of the fault appears as a narrow Valley slicing across the plane near San Francisco a prominent feature along this fault is San Andreas Lake the lake fills a depression that developed along the plate boundary at low tide the seashore also reveals a startling view of a branch of the fault over millions of years this plate movement has been sufficient to displace huge blocks of the crust here looking South two different types of rock lie side by side the rocks are situated on two plates that are moving past each other an earthquake strikes Southern California the shock waves are recorded on this seismograph the occurrence of earthquakes in California is not surprising because these great Earth tremors are commonly generated along plate boundaries in California earthquakes have already caused extensive damage to property and claimed many lives in other parts of the world such as here in Turkey earthquakes are also associated with plate boundaries they serve as a constant reminder of the tremendous forces that are involved in plate movement [Music] plate boundaries also control the global distribution of certain mineral resources for example large sedimentary basins which may contain oil and gas form along the margins of the continents Metals such as copper iron and even gold may also be concentrated as a result of magma intrusions and vol canic activity associated with subduction zones but what evidence do we have that the plates have actually moved we think of Earth's magnetic North and South poles as we know them today but actually they have switched north south polarity at irregular intervals through geologic time as certain rocks form magnetic particles in these rocks respond to the magnetic field of the earth and are aligned magnetically ships to a magnetometers over the Mid-Atlantic Ridge have detected magnetic banding the up and down pattern on the graph reflects the levels of magnetic attraction in the Rocks note that the pattern on one side is a mirror image of the other as the sea Flor spreads cooling lava becomes magnetized by the prevailing magnet magnetic field these symbols illustrate polarity as we know it today these symbols represent reversals in polarity more lava extrudes developing new sea floor and additional symmetric magnetic banding forms as older lavas move outward from the crest thus the magnetic banding reveals that the plates are moving away from each other now scientists are drilling into the ocean floor itself to obtain evidence from the sediments and underlying rocks the glomar Challenger is a ship with capabilities for drilling and removing samples of seafloor many kilometers below the ocean surface when core samples are brought aboard ship they are carefully removed and wrapped the samples contain layers of sediment and rock some samples are immediately taken to the laboratory aboard ship here they are analyzed and studied for texture chemical content and fossils knowing the ship's precise location is of utmost importance in position positioning The Vessel over a specific point on the sea Flor the glomar Challenger operates during the nighttime hours as well collecting samples to be made available to scientists around the [Music] world each core sample is split in half labeled and classify scrips Institute of oceanography is one place where representative ocean samples are analyzed age relationships are documented by the fossils of the sediments a startling picture is emerging from these samples the ocean floor is relatively Young when compared to the land masses samples show that the seaf floor is youngest at the Mid-Atlantic Ridge Crest and is progressively older toward the edges of the ocean Basin at the ages of the rocks on the sea floor are known the combination of time and distance May indicate the rate at which new seaf Flor forms this averages between 2 and 5 cm a year which is a substantial figure it amounts to 6 m in a century and means for example that the Atlantic Ocean is 30 m wider than when it was first crossed by Christopher Columbus this diagram shows the ages of the rocks in millions of years ages are identical on both sides of the ridge even strong longer evidence is provided by direct observation of the seaf Flor this was first made possible through project famous a Cooperative venture between France and the United States Dives made by the submersible Alvin allowed scientist to explore the central Rift Valley and adjacent fracture zones along the Mid-Atlantic Ridge Crest Alvin enabled a three-man crew to dive several kilometers to take the first real look at an active Ridge and identify the geologic processes which occur at spreading plate boundaries the Alvin kept in full communication with the ship Lulu and its die positioning was carefully monitored Alvin's slow descent took the researchers to places where no human has ever been before on the ocean floor they observe lava formations different from any lava flows that originate on land known as phillow lavas these extrusions occurred Beneath the Sea and were observed along the central Rift zone of the Mid-Atlantic Ridge this rare Motion Picture footage shot off the coast of Hawaii enable geologists to see how pillow lava forms water rapidly cools the lava forming the pillow-shaped masses near San Francisco similar masses of pillow lava are exposed originally formed by volcanic action Beneath the Sea the forces of the colliding Pacific and North American plates have pushed this pillar lava above sea level the Terrace coast of California also consists of pieces of this ancient seafloor pushed up along the edge of the continent the old seaf Flor is now the mountainous Ridge along the west coast additional evidence is found near San Francisco where a type of rock called chur forms a cliff at a mountain along the California coast these layers of CH are twisted and folded but an electron microscope reveals something very unusual about this rock fossil radians become visible these small organisms lived in the ocean and when they died their remains fell to the bottom and formed layers of soft ooze on the seaf Flor in time these skeletons were cemented together to form layers of hard rock but what causes the Earth's crustal plates to move a popular concept is that convection occurs within Earth's metal and that these intermittent movements transport the plates in conveyor belt fashion the nature of these convection currents is not thoroughly understood another concept involves regions of concentrated heat flow at Earth's surface commonly known as hotpots some geologists believe that hotpots Mark the positions of rising magmatic material known as plumes many of the hottest lava flows ever recorded are found in Hawaii some scientists think that there is a plume located in the matal beneath these islands this plume could explain the formation of the Hawaiian island chain as the ocean floor moves intermittently Northwest over this presumed hot spot at about 13 cm a year the plume produces a succession of new volcanoes these volcanoes in turn migrate with the moving plate away from the Hotpot to form the island chain movement of continents over hotspots may cause new oceans to form such may be the case with the Red Sea the Arabian Peninsula is moving away from the continent of Africa the Red Sea and the Gulf of Aiden represent two of the newest seaways created by the spreading of an ocean floor scientists speculate that this movement could be due to a hot spot within the Earth's metal some scientists believe that another hot spot is located beneath Yellowstone National Park providing a major display of geyser and hotring phenomena Yellowstone is a place where subsurface heat may be creating movement that could cause the formation of a new ocean but this may not happen for millions of years we are accustomed to the way this planet looks today but the plates of the Earth's crust are in constant movement the Earth's surface of today will not be the surface of tomorrow as the plates continue to move the Continental masses May Come Together Again again as they have in the past to form another supercontinent in time they may once more drift apart the study of plate tectonics leads to a fuller understanding of the Earth's internal unrest that causes constant change on our [Music] planet for [Music]