WEBVTT - How Do Plate Tectonics Work?

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<v Speaker 1>Welcome to brain Stuff, a production of iHeart Radio, Hey

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<v Speaker 1>brain Stuff Lauren Vogelbaum here. Back in nineteen eleven, a

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<v Speaker 1>German meteorologist and geophysicist named Alfred Wegner was doing research

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<v Speaker 1>at a university library when he came upon a scientific

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<v Speaker 1>paper that listed ancient fossils of identical plants and animals

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<v Speaker 1>that have been found on both sides of the Atlantic Ocean.

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<v Speaker 1>This Scott Wagener to thinking about how the same organisms

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<v Speaker 1>could have evolved in two places that were separated by

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<v Speaker 1>thousands of miles of water. Some scientists believed that land

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<v Speaker 1>bridges had once existed between these places, but Vagener looked

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<v Speaker 1>at maps of the coastlines of Africa and South America

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<v Speaker 1>and came up with a different idea. What if those

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<v Speaker 1>continents had once been joined together and then moved apart

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<v Speaker 1>as part of a process that was still going on.

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<v Speaker 1>From that inspiration, Wagner came up with his theory of

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<v Speaker 1>continental drift, which at the time was widely derided as ridiculous.

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<v Speaker 1>By the nineteen fifties and sixties, however, scientists had come

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<v Speaker 1>around to thinking that Vagner might have been onto something,

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<v Speaker 1>and that pieces of the Earth's crust are slowly moving,

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<v Speaker 1>a process that not only explains many of the planet's

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<v Speaker 1>features but also helped make life on Earth possible. Plate

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<v Speaker 1>tectonics is the theory that the Earth's crust and upper

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<v Speaker 1>mantle are composed of numerous major and minor plates that

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<v Speaker 1>fit together tightly but are in continuous motion, moving sometimes

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<v Speaker 1>toward one another and other times apart. That movement is

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<v Speaker 1>known as plate motion or tectonic shift, and it's been

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<v Speaker 1>going on for a long long time. A study by

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<v Speaker 1>Johns Hopkins University researchers published in August of twenty nineteen

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<v Speaker 1>in the scientific journal Nature, concludes that plate tectonics began

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<v Speaker 1>about two point five billion years ago and has developed

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<v Speaker 1>gradually since then. For the article, this episode is based

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<v Speaker 1>on How Stuff Works. Spoken by email with Ray Russo,

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<v Speaker 1>an associate professor of geology at the University of Florida

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<v Speaker 1>and an expert in plate tectonics, He explained, the Earth

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<v Speaker 1>is a large scale heat engine. Heat left over from

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<v Speaker 1>planetary accretion, from gravitational compression, and from radioactive decay is

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<v Speaker 1>trapped in the Earth's interior. Because heat flows from warm

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<v Speaker 1>to cold regions, the Earth's interior heat tends to flow

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<v Speaker 1>toward its cold surface. The most efficient way for this

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<v Speaker 1>heat to get from the deep interior to the Earth's

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<v Speaker 1>surface is by convection. So on a large scale, hot

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<v Speaker 1>mantle material rises and replaces cold mantle material that has

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<v Speaker 1>developed at Earth's surface. He continued. The cold material is

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<v Speaker 1>essentially the Earth's rigid plates. These plates become dense as

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<v Speaker 1>they cool, and eventually they become dense enough to sink

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<v Speaker 1>into the mantle, cooling the planet, disturbing the mantle on

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<v Speaker 1>a global scale. In a nutshell, that's plate technonics. The

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<v Speaker 1>plates move really, really slowly. The average speed is just

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<v Speaker 1>zero point six inches or one point five centimeters per year,

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<v Speaker 1>though scientists have differing opinions on whether the movement is

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<v Speaker 1>slowing down or increasing. The plates interact along their boundaries

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<v Speaker 1>in three different ways. Where two plates move away from

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<v Speaker 1>each other, it creates a divergent boundary, a zone where

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<v Speaker 1>earthquakes are common and hot magma or molten rock rises

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<v Speaker 1>from the mantle to the surface to form new crust. Conversely,

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<v Speaker 1>in places where two plates come together, a convergent boundary occurs.

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<v Speaker 1>The impact of the plates in those places can cause

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<v Speaker 1>the edges to buckle and push up to form a

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<v Speaker 1>mountain range, or else bend to create a deep trench

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<v Speaker 1>in the ocean floor. Chains of volcanoes often form parallel

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<v Speaker 1>to the boundaries. Convergent boundaries create continental crust but destroy

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<v Speaker 1>rust that's part of the ocean floor. Meanwhile, in a

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<v Speaker 1>transform plate boundary, two plates will slide past one another.

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<v Speaker 1>Crust along a transform plate boundary will be cracked and broken,

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<v Speaker 1>but unlike the other two types of boundaries, it won't

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<v Speaker 1>create any new crust. Earthquakes are common along these faults.

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<v Speaker 1>As Russo explained, plate tectonics profoundly affect our entire planet

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<v Speaker 1>and all of its natural processes. One big reason is

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<v Speaker 1>that some of the movement of the plates causes the

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<v Speaker 1>formation of volcanoes, but basically breaks in the crust that

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<v Speaker 1>serve as vents for heat and lava, and their eruptions

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<v Speaker 1>continually resurface the ocean basins that account for seventy of

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<v Speaker 1>the Earth's surface. Just as importantly, volcanic activity associated with

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<v Speaker 1>tectonic plate movement causes lighter, less dense minerals to separate

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<v Speaker 1>from the heavier, denser ones in the Earth's mantle, which

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<v Speaker 1>results in the development of continents. You know where most

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<v Speaker 1>of us live, and the fertile soil that allows plants

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<v Speaker 1>to grow and produce both food and oxygen that sustains

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<v Speaker 1>humans and large animal life. Tectonic plate movement also helped

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<v Speaker 1>in numerous ways to create the conditions that make life

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<v Speaker 1>on Earth possible. It leads, for example, to the interaction

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<v Speaker 1>of hot volcanic rocks with water in the ocean, and

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<v Speaker 1>the leaching of ions from those rocks is what controls

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<v Speaker 1>the ocean's salinity. Russo explained. Life evolved in the oceans

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<v Speaker 1>in the presence of this ion rich water, and humans,

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<v Speaker 1>for example, have blood salinity equivalent to the salinity of seawater.

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<v Speaker 1>As a direct consequence, by rearranging the configuration of the

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<v Speaker 1>continents and the ocean basins, plate tectonics also influences the

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<v Speaker 1>planet's climate, Russo said. For example, the current shapes of

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<v Speaker 1>the ocean basins continually supply warm equatorial waters to polar regions,

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<v Speaker 1>keeping the planet from developing very great extremes of surface

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<v Speaker 1>temperature between equator and poles. The mountains formed by tectonics

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<v Speaker 1>are also among the planet's most important carbon dioxide sinks,

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<v Speaker 1>helping to draw down atmospheric CEO two levels by forming

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<v Speaker 1>new minerals. That process increases and decreases in response to

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<v Speaker 1>shifts in temperature, enabling the mountains to act as giant thermostats.

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<v Speaker 1>The gradual shifting of the continental masses has also played

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<v Speaker 1>an important role in biological evolution. Russo said, Speciation the

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<v Speaker 1>development of new species, occurs when a single group of

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<v Speaker 1>plants or animals is divided into two groups that are

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<v Speaker 1>no longer in reproductive contact, as for example, often happens

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<v Speaker 1>when a supercontinent breaks up and new ocean basins form

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<v Speaker 1>between its continental fragments. All of this may help explain

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<v Speaker 1>why life is so prevalent on Earth but apparently absent

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<v Speaker 1>on other planets in our Solar System. While Mars and

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<v Speaker 1>Venus have hot interior years and their surfaces show signs

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<v Speaker 1>of recent deformation, Earth is the only planet in the

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<v Speaker 1>Solar System whose surface is divided into plates. Mercury, the

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<v Speaker 1>fourth rocky planet, is no longer geologically active. Today's episode

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<v Speaker 1>is based on the article plate tittonics puts together the

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<v Speaker 1>puzzle of Earth's shifting crust on how stuff Works dot com,

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<v Speaker 1>written by Patrick J. Keaiger. Brain Stuff is production of

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<v Speaker 1>by Heart Radio in partnership with how stuff works dot

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<v Speaker 1>Com and is produced by Tyler Klang. For more podcasts

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