Speaker 1: Welcome to brain Stuff, a production of iHeart Radio, Hey
Speaker 1: brain Stuff Lauren Vogelbaum here. Back in nineteen eleven, a
Speaker 1: German meteorologist and geophysicist named Alfred Wegner was doing research
Speaker 1: at a university library when he came upon a scientific
Speaker 1: paper that listed ancient fossils of identical plants and animals
Speaker 1: that have been found on both sides of the Atlantic Ocean.
Speaker 1: This Scott Wagener to thinking about how the same organisms
Speaker 1: could have evolved in two places that were separated by
Speaker 1: thousands of miles of water. Some scientists believed that land
Speaker 1: bridges had once existed between these places, but Vagener looked
Speaker 1: at maps of the coastlines of Africa and South America
Speaker 1: and came up with a different idea. What if those
Speaker 1: continents had once been joined together and then moved apart
Speaker 1: as part of a process that was still going on.
Speaker 1: From that inspiration, Wagner came up with his theory of
Speaker 1: continental drift, which at the time was widely derided as ridiculous.
Speaker 1: By the nineteen fifties and sixties, however, scientists had come
Speaker 1: around to thinking that Vagner might have been onto something,
Speaker 1: and that pieces of the Earth's crust are slowly moving,
Speaker 1: a process that not only explains many of the planet's
Speaker 1: features but also helped make life on Earth possible. Plate
Speaker 1: tectonics is the theory that the Earth's crust and upper
Speaker 1: mantle are composed of numerous major and minor plates that
Speaker 1: fit together tightly but are in continuous motion, moving sometimes
Speaker 1: toward one another and other times apart. That movement is
Speaker 1: known as plate motion or tectonic shift, and it's been
Speaker 1: going on for a long long time. A study by
Speaker 1: Johns Hopkins University researchers published in August of twenty nineteen
Speaker 1: in the scientific journal Nature, concludes that plate tectonics began
Speaker 1: about two point five billion years ago and has developed
Speaker 1: gradually since then. For the article, this episode is based
Speaker 1: on How Stuff Works. Spoken by email with Ray Russo,
Speaker 1: an associate professor of geology at the University of Florida
Speaker 1: and an expert in plate tectonics, He explained, the Earth
Speaker 1: is a large scale heat engine. Heat left over from
Speaker 1: planetary accretion, from gravitational compression, and from radioactive decay is
Speaker 1: trapped in the Earth's interior. Because heat flows from warm
Speaker 1: to cold regions, the Earth's interior heat tends to flow
Speaker 1: toward its cold surface. The most efficient way for this
Speaker 1: heat to get from the deep interior to the Earth's
Speaker 1: surface is by convection. So on a large scale, hot
Speaker 1: mantle material rises and replaces cold mantle material that has
Speaker 1: developed at Earth's surface. He continued. The cold material is
Speaker 1: essentially the Earth's rigid plates. These plates become dense as
Speaker 1: they cool, and eventually they become dense enough to sink
Speaker 1: into the mantle, cooling the planet, disturbing the mantle on
Speaker 1: a global scale. In a nutshell, that's plate technonics. The
Speaker 1: plates move really, really slowly. The average speed is just
Speaker 1: zero point six inches or one point five centimeters per year,
Speaker 1: though scientists have differing opinions on whether the movement is
Speaker 1: slowing down or increasing. The plates interact along their boundaries
Speaker 1: in three different ways. Where two plates move away from
Speaker 1: each other, it creates a divergent boundary, a zone where
Speaker 1: earthquakes are common and hot magma or molten rock rises
Speaker 1: from the mantle to the surface to form new crust. Conversely,
Speaker 1: in places where two plates come together, a convergent boundary occurs.
Speaker 1: The impact of the plates in those places can cause
Speaker 1: the edges to buckle and push up to form a
Speaker 1: mountain range, or else bend to create a deep trench
Speaker 1: in the ocean floor. Chains of volcanoes often form parallel
Speaker 1: to the boundaries. Convergent boundaries create continental crust but destroy
Speaker 1: rust that's part of the ocean floor. Meanwhile, in a
Speaker 1: transform plate boundary, two plates will slide past one another.
Speaker 1: Crust along a transform plate boundary will be cracked and broken,
Speaker 1: but unlike the other two types of boundaries, it won't
Speaker 1: create any new crust. Earthquakes are common along these faults.
Speaker 1: As Russo explained, plate tectonics profoundly affect our entire planet
Speaker 1: and all of its natural processes. One big reason is
Speaker 1: that some of the movement of the plates causes the
Speaker 1: formation of volcanoes, but basically breaks in the crust that
Speaker 1: serve as vents for heat and lava, and their eruptions
Speaker 1: continually resurface the ocean basins that account for seventy of
Speaker 1: the Earth's surface. Just as importantly, volcanic activity associated with
Speaker 1: tectonic plate movement causes lighter, less dense minerals to separate
Speaker 1: from the heavier, denser ones in the Earth's mantle, which
Speaker 1: results in the development of continents. You know where most
Speaker 1: of us live, and the fertile soil that allows plants
Speaker 1: to grow and produce both food and oxygen that sustains
Speaker 1: humans and large animal life. Tectonic plate movement also helped
Speaker 1: in numerous ways to create the conditions that make life
Speaker 1: on Earth possible. It leads, for example, to the interaction
Speaker 1: of hot volcanic rocks with water in the ocean, and
Speaker 1: the leaching of ions from those rocks is what controls
Speaker 1: the ocean's salinity. Russo explained. Life evolved in the oceans
Speaker 1: in the presence of this ion rich water, and humans,
Speaker 1: for example, have blood salinity equivalent to the salinity of seawater.
Speaker 1: As a direct consequence, by rearranging the configuration of the
Speaker 1: continents and the ocean basins, plate tectonics also influences the
Speaker 1: planet's climate, Russo said. For example, the current shapes of
Speaker 1: the ocean basins continually supply warm equatorial waters to polar regions,
Speaker 1: keeping the planet from developing very great extremes of surface
Speaker 1: temperature between equator and poles. The mountains formed by tectonics
Speaker 1: are also among the planet's most important carbon dioxide sinks,
Speaker 1: helping to draw down atmospheric CEO two levels by forming
Speaker 1: new minerals. That process increases and decreases in response to
Speaker 1: shifts in temperature, enabling the mountains to act as giant thermostats.
Speaker 1: The gradual shifting of the continental masses has also played
Speaker 1: an important role in biological evolution. Russo said, Speciation the
Speaker 1: development of new species, occurs when a single group of
Speaker 1: plants or animals is divided into two groups that are
Speaker 1: no longer in reproductive contact, as for example, often happens
Speaker 1: when a supercontinent breaks up and new ocean basins form
Speaker 1: between its continental fragments. All of this may help explain
Speaker 1: why life is so prevalent on Earth but apparently absent
Speaker 1: on other planets in our Solar System. While Mars and
Speaker 1: Venus have hot interior years and their surfaces show signs
Speaker 1: of recent deformation, Earth is the only planet in the
Speaker 1: Solar System whose surface is divided into plates. Mercury, the
Speaker 1: fourth rocky planet, is no longer geologically active. Today's episode
Speaker 1: is based on the article plate tittonics puts together the
Speaker 1: puzzle of Earth's shifting crust on how stuff Works dot com,
Speaker 1: written by Patrick J. Keaiger. Brain Stuff is production of
Speaker 1: by Heart Radio in partnership with how stuff works dot
Speaker 1: Com and is produced by Tyler Klang. For more podcasts
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