AST101 Unit 2, Ch6: The Earth

What are some of the most common elements composing the earth's crust, mantle, and core?

-crust: oxygen, silicon, aluminum -mantle: calcium, magnesium, iron (silicates) -core: iron, nickel (liquid outer, solid inner)

How is the aurora related to earth's magnetic field?

As charged particles flow toward the magnetic poles, they generate electric currents in the upper atmosphere. These currents, circulating around the magnetic poles, drive electrons along the mahnetjc field lines. The moving electrons spiral around the field lines, colliding with molecules of nitrogen and oxygen. Such collisions excite atmospheric gases, lifting their electrons to higher energy orbitals. As the electrons drop back to lower orbitals, they emit the light we see as aurora.

What is precession? What are some of its possible consequences?

As the Earth moves around the Sun over long periods of time, the direction in which its rotation axis points changes very slowly. This motion, similar to the wobble that occurs when a spinning coin or toy top begins to slow down, is called precession. Possible consequences consist of changing climate and even ice ages if the earth's tilt and eccentricity of its orbit change drastically enough.

Why is the earth round? Is it perfectly spherical?

Gravity makes the earth round, but it is not perfectly spherical. The earth bulges at its equator due to rotation.

On what plate of crust are you located? Which way is it taking you?

North American, out and away from its estimated origin

What are two explanations that scientists offer for why the interior of the earth is hot? How hot is it?

One theory is that the earth was born hot, and constant impacts only made it hotter and hotter. Another theory is that the earth was born cold, and the natural radioactivity in the earth's interior made it hot. The earth's core is 120,000K.

What were the main components of the atmosphere when the earth formed, and what are the main components today? How and why did they changes?

Our planet's anceint atmosphere contained a lot more methane and ammonia. The main components today are nitrogen, oxygen, and hydrogen. Photosenthesis adds oxygen to our atmosphere continually, and volcanic eriptions add nitrogen, water, and carbon dioxide to our atmosphere even today.

What is ozone? Why is it important?

Ozone is a gas made of molecules containing three oxygen atoms that, in the upper atmosphere, absorbs harmful UV radiation.

What is happening where one tectonic plate is smashing into another?

Plate Tectonics -- Subduction

How can scientists determine the age of the earth?

Radioactive dating of rocks

Summary of Chapter 6

The Earth is roughly spherical, and its radius is about 6400 kilometers (4000 miles). Trace amounts of radioactivity in rocks here and elsewhere in the Solar System reveal that the Earth formed about 4.6 billion years ago. Radioactive material also adds heat to its interior. The flow of heat to the Earth's surface stirs slow convective motions, which shift the Earth's crust (plate tectonics), creating mountains, volcanoes, ocean basins, and earthquakes. The waves generated by earthquakes (seismic waves) allow us to study the Earth's interior. They show it is stratified into four distinct regions: a very thin crust of ordinary rock, a mantle of hot but essentially solid silicates, an outer core of liquid iron and nickel, and an inner core of solid iron and nickel. Currents created by motions in the Earth's core generate the Earth's magnetic field. That field in turn affects the motion of charged particles in the upper atmosphere. Such particles may create auroral displays when they collide with oxygen and nitrogen in the upper atmosphere. The nitrogen, carbon dioxide, and water of our atmosphere may have come from volcanic gases vented over the Earth's history. Alternatively, these atmospheric gases may be the evaporated remains of comets that hit the Earth in its infancy. Plant life has created the atmosphere's oxygen by photosynthesis. Oxygen, and the ozone created when oxygen is broken apart, absorbs ultraviolet radiation from the Sun, thereby protecting us from its biologically harmful effects. Carbon dioxide and water vapor absorb infrared radiation, trapping heat radiated from the Earth's surface. By slowing heat loss from our planet into space, these gases create the greenhouse effect and make Earth slightly warmer than it would be if the infrared radiation could escape freely. The Earth's spinning motion creates a Coriolis effect that deflects objects moving over its surface. The Coriolis effect makes large storm systems rotate and is essential for driving the circulation of the atmosphere and the oceans. The Earth's axis also wobbles (precesses) over a period of 26,000 years.

What is convection? What are some other examples of convection besides hot soup?

The circulating movement of heated liquid or gas (heating=rising, cooling=sinking). Some examples are boiling water and convection currents in the ocean.

What factors are thought to be responsible for the earth's magnetic field?

The earth's rotation and convection currents in the molten core

What is the Coriolis Effect?

The effect of Earth's rotation on the direction of winds and currents.

How does the fact that the earth has a magnetic field help provide evidence for the theory of plate tectonics?

The magnetic field is partly caused by convection in the core, supporting plate tectonics in that it is possible for them to move be ause of the moving materials below it.

Explain how the greenhouse effect works and how it relates to global warming.

The transparency of the Earth's atmosphere to visible radiation allows sunlight to enter the atmosphere and reach the Earth's surface. The energy of the photons is absorbed by surface materials, heating them. The warmed surface radiates infrared energy, but the atmosphere is not very transparent at infrared wavelengths, largely due to water vapor and carbon dioxide. This reduces the heat loss and makes the surface warmer than it would be if the infrared energy could escape freely.

How do we know that the earth has a liquid core? Why is the inner core solid even though it is hotter than the liquid outer core?

We know the earth has a liquid core due to sesmic waves. Seismic waves are classified as either S or P waves, and S waves only travel through solids. Since S waves aboid the core of the earth, we can conclude that it is loquid. The inner core of the earth is solid rather than liquid because of the immense pressure causing atoms to lock in place.

What is the relation bewteen rising and sinking material in the earth's interior and subduction and rifting?

When hot material rises up, it spreads out and flows parellel to the crust, dragging the surface layers and shifting and stretching the crust (rifting). In other places, one piece of crust can be forced to collide with another, driving one piece beneath the other (subduction).