How the Earth Works

If you could view Earth's history at high speed, you'd see continents whiz about, ocean basins grow and shrink, and mountain ranges rise and erode away. This lecture sets the stage for investigating our dynamic planet.

Discovering Earth's exact age took centuries of detective work. Rock strata provide relative ages, but only with the discovery of radioactivity was it possible to determine the absolute geologic timescale.

Analysis of seismic waves from earthquakes allows scientists to map the structure inside Earth. Using this technique, we take a modern-day journey to the center of the Earth in the style of Jules Verne.

We reverse the direction of the previous lecture to see how heat flows from the center of Earth toward the surface, exploring the phenomena of heat radiation, conduction, and convection.

The theory of plate tectonics accounts for the existence of continents, oceans, mountains, earthquakes, volcanoes, mineral resource distribution, climate changes, and many other aspects of our planet.

We investigate the big bang and the early evolution of the universe to learn the origin of atoms, stars, and planets. The supernovae of dying stars played a key role in forging heavy elements.

The solar system formed 4.6 billion years ago when a cloud of gas, dust, and ice began to collapse and rotate, with Earth accreting in the inner region of the disk. An enormous collision with the proto-Earth produced the Moon.

Though rocks may seem eternal, they are part of a continuous cycle of changing forms called the rock cycle, which begins with igneous rocks and can involve sedimentary and metamorphic phases.

Rocks are made of minerals, which in turn are composed of different elements. Silicon and oxygen are the two most abundant elements in Earth's mantle and crust, and most rocks contain them.

Most magma is generated beneath mid-ocean ridges, where plates move apart and rock moves toward the surface to fill the gaps. Magma forms in these places due to a process called pressure release.

When magma cools below certain temperatures, solid mineral crystals begin to grow. With continued cooling the entire magma will eventually crystallize, and the result is an igneous rock.

Volcanoes form where magma reaches the surface and erupts—at which point the magma becomes lava. The different kinds of volcanoes are related to the tectonic settings in which they occur.

Most rock of the crust and mantle is solid. And yet, over long timescales, the crust and mantle are in motion, bending and flowing. This lecture shows how rocks deform in an elastic, plastic, or brittle manner.

More than 200,000 earthquakes are recorded each year. We examine the types of faults along which they occur and the aftermath, which in some cases can leave the Earth ringing like a gong for months.

Continents move because they are the surface expression of mantle convection. Two main forces are directly responsible for plate motions: slab pull and ridge push.

The seafloor shows a tremendous diversity of features that are related to plate tectonics and the process of mantle convection.

Oceans undergo reincarnation: they repeatedly die and are reborn. The Atlantic Ocean is only 180 million years old and will eventually close up again. The Red Sea appears to be a new ocean in the making.

The San Andreas is a transform fault that separates the North American and Pacific plates. Transform faults are actually rare on land, but mid-ocean ridges are intersected by countless such features.

Subduction zones are the most geologically exciting places on Earth. Here the most destructive earthquakes and volcanoes occur, and forces are generated that may rip supercontinents apart.

When plate motions bring continents in contact with each other, the result is the formation of mountains. A notable example is the Himalayas, produced by the continental collision of India with China.

For years intraplate volcanoes such as those that produced the Hawaiian Islands were lumped together under the catch-all name of "hot spots," but recent work is showing that Earth has many different ways of making a volcano.

The largest earthquakes and volcanic eruptions release as much energy as the simultaneous explosion of tens of thousands of nuclear weapons. We look at the human consequences of these events.

Volcanoes can be easily monitored, and they reveal many clues to an impending eruption as the magma slowly forces its way toward the surface. Earthquakes, by contrast, are not yet predictable.

We examine the eruption of Mount St. Helens on May 18, 1980, triggered when an earthquake caused a gigantic avalanche that released pent-up magma and gases, leveling trees for over 600 square kilometers.