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