Chapter 7 Notes

Chapter 7:

Earth and the Terrestrial Worlds

7.1 Earth as a planet

Why is Earth geologically active?

Earth's surface is continually being reshaped by volcanic eruptions, earthquakes, erosion, and other geological processes. Most is the result of what goes on deep inside our planet.

Core

The highest-density material, mostly made of metals.

Mantle

Rocky material of moderate density, mostly minerals.

Crust

The lowest-density rock, such as granite and basalt forms the thin crust, essentially representing the world's outer skin.

Lithosphere

A planet's outer layer of cool, rigid rock.

-Earth and other terrestrial worlds were once hot enough inside for their interiors to melt, allowing material to settle into layers of differing density.

Convection

The process by which hot material expands and rises while cooler material contracts and falls.

(Larger planets retain internal heat much longer than small ones, and this heat drives geological activity.)

Magnetic Field

Generated by the motions of molten metal in its liquid outer core.

Magnetosphere

A kind of protective bubble that surrounds our planet.

Aurora

The few particles that make it through the magnetosphere tend to be channeled toward the poles, where they collide with atoms and molecules in our atmosphere.

What processes shape Earth's surface?

Virtually all geological features originate from impact cratering, volcanism, tectonics, and/or erosion.

Impact Cratering

The excavation of bowl-shaped impact craters by asteroids or comets crashing into a planet's surface.

Volcanism

The eruption of molten rock, or lava, from planets interior onto its surface.

Tectonics

The disruption of a planet's surface by internal stresses.

Erosion

The wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather.

-Like all terrestrial worlds, Earth was bombarded by impacts when it was young, but most ancient craters have been erased by other geological processes.

-Earth's atmosphere and oceans were made from gasses released from the interior by volcanic outgassing.

Plate tectonics

The underlying mantle convection fractured Earth's lithosphere into more than a doze pieces. These plates move under, over, and around each other.

(Tectonics and Volcanism generally occur together because both require internal heat and therefore depend on a planet's size.)

Sedimentary Rock

Erosion has piled sediments into layers on the floors of oceans and seas.

How does Earth's atmosphere affect the planet?

Ozone

Resides primarily in the stratosphere. Absorbs the Sun's dangerous ultraviolet radiation, while the X ray are absorbed by atoms and molecules higher up in Earth's atmosphere.

Greenhouse Effect

Keeps Earth's surface much warmer than it would be otherwise, allowing water to stay liquid over most of the surface.

Greenhouse Gasses

Gasses that are particularly good at absorbing infrared light.

7.2 The Moon and Mercury: Geologically Dead

Was there ever geological activity on the Moon or Mercury?

Lunar Maria

Looks smoother and darker.

-The Moon's dark, smooth maria were made by floods of molten lava billions of years ago, when the Moon's interior was heated by radioactive decay.

-Mercury's craters are less crowded together suggesting that molten lava later covered up some of the craters.

7.3 Mars: A victim of Planetary Freeze-Drying

What geological features tell us that water once flowed on Mars?

-Dried up riverbeds and other signs of erosion show that water flowed on mars in the distant past.

-Images and spectra indicating the presence of clay minerals on the crater floor, presumably deposited by sediments flowing down the river. 

-"Blueberries" found in rocks and indentations suggesting that they formed in standing water.

-Gullies on crater walls suggest that water might still occasionally flow on Mars.

Why did Mars change?

Mars underwent permanent climate change about 3 billion years ago, when it lost much of its atmospheric carbon dioxide and water to space.

(Early in its history, Mars probably had a dense atmosphere from volcanic outgassing, with a stronger greenhouse effect than it has today.)

7.4 Venus: A Hothouse World

Is Venus geologically active?

-Venus shows features of volcanism and tectonics.

(Venus's lack of Earth-like plate tectonics poses a scientific mystery, but may arise because Venus has a thicker and stronger lithosphere than Earth.)

Why is Venus so hot?

Venus's thick carbon dioxide atmosphere creates the extremely strong greenhouse effect that makes Venus so hot.

Carbonate Rocks

Rock rich in carbon and oxygen.

7.5 Earth as a Living Planet

What unique features of Earth are important for life?

-Surface liquid water, atmospheric oxygen, plate tectonics, and climate ability.

(Without life, there would be no oxygen on Earth's atmosphere.)

Seafloor Crust

Mantle material rises upward and erupts to the surface along mid-ocean ridges, becoming new crust for the seafloor.

Subduction

A piece of seafloor crust gradually makes its way across the ocean bottom, then recycles into the mantle.

-Earth has remained habitable for billions of years because its climate is kept stable by the natural action of the carbon dioxide cycle.

How is human activity changing out planet?

Human activity is rapidly increasing the atmospheric concentrations of greenhouse gasses, causing the global average temperature to rise.

What makes a planet habitable?

Earth is habitable because it is large enough to remain geologically active and located at a distance from the Sun where oceans were able to form.