Astronomy Ch. 7 – Earth

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The crust of the Earth is covered by about ________ water in the hydrosphere.


Which of the following layers of the earth is unique among the terrestrial planets?


Compared to the density of water, our Earth averages:

about 5 times denser, like the Mercury and Venus.

The relative size of the atmosphere layer as compared to the solid part of Earth is most similar to

the skin of a grape as compared to the meat of the grape.

What can we conclude about the structure of Earth’s interior knowing that the average density of Earth is higher than the average density of the rock on the continents and seafloor?

that Earth’s most dense material must be beneath the surface

From the center outward, the correct order is:

solid metallic inner core, molten metal outer core, silicate mantle and crust.

The relative size of the mantle of Earth compared to the solid inner core of Earth is most similar to

the meat of a cherry as compared to the pit of the cherry.

Without the greenhouse effect operating in our atmosphere,

Earth would have an average temperature of -23 degrees Celsius.

How is the existence of Earth’s unique atmosphere explained?

the oxygen in Earth’s atmosphere is a result of early life on Earth

What gas is the primary constituent of our atmosphere?


Which major atmospheric component is chiefly a product of life processes?


The critical part of the atmosphere for protecting life on the ground from excessive ultraviolet radiation is the:

ozone layer.

In what part of our atmosphere do we live?


Which parts of the Sun’s radiation are responsible for heating Earth’s surface?

the visible and the infrared

What is the process that physically transfers heat from a lower (hotter) to a higher (cooler) level?


Which of these gases are outgassed from our volcanic eruptions?

water vapor, methane, carbon dioxide.

Above about 100 km, the high-energy portion of the Sun’s radiation spectrum breaks down molecules into atoms. What is this part of Earth’s atmosphere called?

the ionosphere

What is the hole in the ozone layer is thought to be caused by?


The principal greenhouse gases in our present atmosphere are:

water vapor and carbon dioxide.

Almost all of our atmospheric gases lie in the:


The Greenhouse Effect works by trapping

outgoing infrared radiation from the Earth.

Clouds form primarily at the boundary between

the troposphere and the stratosphere.

What is the percentage of Earth’s atmosphere (by volume) that is carbon dioxide (CO2)?


Within Earth’s atmosphere the ozone layer is located

in the stratosphere.

Within Earth’s atmosphere, in which layer does convection occur?

the troposphere

When water vapor condenses out at the cool tops of convection cells, what happens?

clouds form

Which are places on Earth where convection is operating on a grand scale, creating conditions important to life on Earth?

in the troposphere, such as a summer thunderstorm; at the thermal vents in the rift valleys; in the mantle; in hot springs like Old Faithful; All of the above are good examples.

In what scenario is the blue component of incoming sunlight is scattered much more than any other color component?

when the sun is high in the sky

Why is the sky blue?

the atmosphere scatters the light from the Sun

We determine the structure of the Earth’s core using

seismic wave data.

Seismic waves are most useful for mapping:

the Earth’s core and mantle.

Like other solid bodies in the solar system, Earth’s surface was kept molten by

bombardment by small bodies.

In noting that our world is "differentiated," we mean that:

the iron and nickel core is denser than the silicate mantle and crust.

Which statement about seismic waves is true?

P waves travel faster, and thus arrive sooner than do the S waves.

Which statement about seismic waves is FALSE?

Only P waves can be detected in the shadow zone.

The oldest rocks on our crust are radioactively dated at about:

four billion years old.

When two tectonic plates collide:

they continue moving, producing a variety of large deformations.

A region where a denser basaltic plate is subducted under a continental one is:

the Nazca Trench.

Which of these is not a product of plate tectonics and hot spots?

the Grand Canyon’s eroded depths

When strong solar winds are displaced poleward by our magnetic fields, we get:

intense auroral displays.

The region around Earth where the magnetic field traps charged particles is the:

Van Allen Radiation Belts.

The presence of a magnetic field is a good indication that:

we have a liquid metal outer core, spinning rapidly as we rotate.

The Dynamo Theory holds that:

magnetic fields are generated by rapidly spinning, fluid magnetic interiors.

Earth’s magnetic field:

prevents charged particles in the solar wind from reaching the surface.

What is the best description of the Earth’s rotation over its entire history?

It has slowed down very gradually at about .0015 seconds per century.

Which body has the greatest gravitational pull on Earth?

the Sun

At what phase are the tides least noticeable?

third quarter

What is true of spring tides?

The difference between low and high tides would be greatest.

At what phase would tidal variation be the least during the entire day?

first quarter

(SA) In plate tectonics, how are trenches formed? What always accompanies them?

Trenches are the deep places in the oceans where denser basaltic plates are subducted beneath lighter continental ones. The heat of this subduction always gives rise to volcanic chains immediately above the subduction zone, such as the Nazca Trench off South America and the Andes immediately east of it.

(SA) How do earthquakes allow us to model the structure of Earth’s core?

Examining the different seismic waves we find P and S waves are not recorded by all over the planet. There is a blind spot for S waves on the side of Earth opposite the earthquake, and there is a shadow zone part way around the surface from the earthquake. Since we know S waves cannot travel through liquid and P waves can, we conclude the Earth’s core is liquid. Since P waves bend when they enter the liquid core, but some travel straight through, it implies there is a solid center to the liquid outer core.

(SA) Why do volcanic mountain chains, such as the Andes, accompany deep trenches like the Nasca Trench off South America?

When plate tectonics causes a denser oceanic plate beneath a moving continent, the basalt sinks down into a deep trench, but the heat of subduction causes molten magma to rise up under the edge of the continent, creating volcanoes.

(SA) Describe several features on the earth’s crust explained by plate tectonics.

Mountain ranges, volcanic mountain chains, mid-ocean rifts, oceanic trenches, faults, earthquakes, and plate motion.

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