How much earth science is on the GED?

Earth and space science is about 20 percent of the Science test.

What causes the seasons?

Earth's roughly 23.5-degree axial tilt, which changes how directly sunlight strikes each hemisphere through the year.

GED Earth and Space Science Practice

Earth and space science is about 20 percent of the GED Science test: the smallest share, and the most fact-driven. A short study session here often produces the fastest score gain.

Question 1 of 30

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After a wildfire burns the trees and brush on a steep hillside, officials warn nearby homes about mudslides during the next heavy rain. Why does the fire raise the risk of mudslides?

Earth and space science study guide

Earth and space science is the smallest of the three science areas, but its questions are often among the most readable. Most rely on a map, diagram, or chart. This guide covers the processes those graphics usually show.

Earth’s structure and plate tectonics

Earth has a thin outer crust, a thick mantle, and a core. The crust and upper mantle are broken into plates that move slowly over the softer layer beneath them.

Where plates meet, three things can happen. At divergent boundaries they pull apart and new crust forms, as along mid-ocean ridges. At convergent boundaries they push together, building mountains or forcing one plate under another, which leads to volcanoes and deep trenches. At transform boundaries they slide past each other, which causes earthquakes, as along the San Andreas Fault.

Rocks and the rock cycle

Igneous rock forms when melted rock cools. Sedimentary rock forms when layers of sediment are pressed and cemented together; it is where most fossils are found. Metamorphic rock forms when existing rock is changed by heat and pressure without melting.

In undisturbed sedimentary layers, the lowest layers are the oldest. This principle, called superposition, lets scientists put fossils and events in order even without exact dates.

The water cycle and weather

The sun drives the water cycle. Water evaporates from oceans and lakes, plants release water through transpiration, the vapor condenses into clouds, and it returns as precipitation that runs off into bodies of water or soaks into the ground.

Weather is the short-term condition of the atmosphere; climate is the long-term pattern in a region. Warm air rises and cool air sinks, and the boundaries between air masses, called fronts, bring changes in weather. A cold front often brings sudden storms, while a warm front tends to bring slower, steadier rain.

Natural resources and human impact

Renewable resources, such as sunlight, wind, and water, are replaced naturally on a human time scale. Nonrenewable resources, such as coal, oil, and natural gas, formed over millions of years and are used far faster than they form.

Questions often ask you to weigh trade-offs using data: the cost of a power source against its emissions, or the effect of farming practices on soil. Use only what the provided data supports, not what you have heard elsewhere.

The solar system and beyond

Earth’s rotation on its axis causes day and night. Its revolution around the sun takes one year. Seasons come from the tilt of Earth’s axis, not from changes in distance to the sun: the hemisphere tilted toward the sun receives more direct light and has summer.

The moon’s phases come from how much of its sunlit side we see as it orbits Earth. Tides are caused mainly by the moon’s gravity. The sun is a star, one of billions in the Milky Way galaxy.

Natural hazards and warning signs

A natural hazard is an Earth process that can harm people or property. GED questions about hazards usually give you a scale, a data table, or a short safety notice and ask what it means. Learn the main hazards by their cause and by the signs scientists watch for.

Earthquakes are measured on a magnitude scale where each whole number up means about 10 times more ground shaking. A strong earthquake under the ocean can lift a huge amount of water and start a tsunami, a series of long waves that cross deep ocean at roughly the speed of a jet airliner and grow tall as they reach shallow water. Volcanoes often give warnings before they erupt: more small earthquakes, swelling ground, and new gas from vents all suggest that magma is rising. These signs raise the risk but cannot fix an exact eruption date.

Weather hazards follow the same pattern. Hurricanes are ranked by sustained wind speed, from Category 1 to Category 5. Heavy rain causes floods when water arrives faster than soil can absorb it. Human choices can raise the risk: paving over land increases runoff, and clearing or burning plants on a slope leaves the soil with no roots to hold it, which makes mudslides more likely.

Name the cause of a hazard before judging its risk.
Treat warning signs as rising risk, not as proof of an exact date.
Look for human actions, such as paving or clearing land, that make a hazard worse.

Worked example

An undersea earthquake starts a tsunami 2,100 km from a coastal town. Over deep ocean, the waves travel at about 700 km per hour. About how long do people in the town have before the waves arrive?

Use time = distance ÷ speed.
Divide: 2,100 km ÷ 700 km per hour = 3 hours.
Check the trap answer: multiplying 2,100 × 700 gives a huge number that is not a time at all, so division is the right operation.
The town has about 3 hours, which is why warning centers track earthquakes as soon as they happen.

Climate and the greenhouse effect

Climate is the average pattern of temperature and precipitation in a place over about 30 years or more. A single cold winter or a hot week tells you about weather, not climate. GED climate questions usually give a graph covering decades, so look at the overall trend rather than one year.

The greenhouse effect keeps Earth warm enough for life. Sunlight passes through the atmosphere and warms the surface. The warm surface gives off infrared energy, and gases such as carbon dioxide, methane, and water vapor absorb part of it before it escapes to space. More of these gases means more heat held near the surface. Burning coal, oil, and natural gas adds carbon dioxide to the air, and measurements show its level has risen steadily since the late 1950s, along with average global temperature.

Warming sets off other changes. Sea level rises because ice on land melts into the ocean and because warmer water expands. Melting sea ice that already floats adds very little water, but losing it exposes dark ocean that absorbs more sunlight, which adds to the warming. When a question shows a trend, separate what the data show from any cause that a choice adds on its own.

Worked example

A climate graph shows carbon dioxide in the air at about 340 parts per million (ppm) in 1980 and about 415 ppm in 2020. What was the average rate of increase per year?

Find the change in carbon dioxide: 415 − 340 = 75 ppm.
Find the time that passed: 2020 − 1980 = 40 years.
Divide the change by the time: 75 ÷ 40 ≈ 1.9 ppm per year.
Check the trap answer: 415 ÷ 40 is about 10.4, which uses the ending value instead of the change, so it is far too large.

Checklist before test day

These ideas cover most earth and space items.

Match each plate boundary type to the landforms it creates.
Use superposition to order rock layers from oldest to youngest.
Trace water through each step of the water cycle.
Separate weather from climate in a question’s wording.
Explain why seasons come from axial tilt, not distance.
Sort energy sources into renewable and nonrenewable.

Earth and Space Science practice set 1: 30 questions with answers

Work each question on paper first, then open the answer to check your reasoning.

1.After a wildfire burns the trees and brush on a steep hillside, officials warn nearby homes about mudslides during the next heavy rain. Why does the fire raise the risk of mudslides?
1. A.Burned slopes soak up rain much faster than healthy forests do
2. B.Without plant roots, soil washes downhill much more easily
3. C.Ash in the air makes the next rainfall much heavier
4. D.The fire melts the rock that lies beneath the soil
Show answer
Answer: B. Without plant roots, soil washes downhill much more easily
Plant roots hold soil in place, so a burned slope loses that grip and heavy rain can carry the soil away. Burned ground usually soaks up less water, not more, so more runoff flows downhill.

2.Scientists monitoring a volcano record the following. Week 1: 5 small earthquakes Week 2: 18 small earthquakes Week 3: 60 small earthquakes The ground near the summit also swelled by 2 cm. Which conclusion is best supported by the data?
1. A.The volcano is cooling down and slowly becoming less active over time
2. B.The swelling shows that magma is draining away now
3. C.Magma may be rising, so the risk of an eruption is growing
4. D.The data prove the volcano will erupt the next day
Show answer
Answer: C. Magma may be rising, so the risk of an eruption is growing
More earthquakes and a swelling summit are signs that magma is moving up and pushing on the rock. The data show rising risk but cannot prove an exact eruption date, so that choice goes too far.

3.At night, the Sun cannot be seen, and thousands of other stars appear only as faint points of light. During the day, the Sun is far too bright to look at. Why does the Sun look so much brighter than other stars?
1. A.It is far closer to Earth than any other star
2. B.It is the largest star in the Milky Way galaxy
3. C.It is a planet that reflects light from stars
4. D.It is the only star that gives off its own light
Show answer
Answer: A. It is far closer to Earth than any other star
The Sun is an average star that looks bright because it is so close to Earth. Many other stars are larger and also make their own light, so those choices are false.

4.Every day, people in a town see the Sun rise in the east, cross the sky and set in the west. What causes this daily pattern?
1. A.The Sun orbits Earth once each day
2. B.Earth spins on its axis once each day
3. C.Earth orbits the Sun once each day
4. D.The Moon blocks the Sun’s light each evening
Show answer
Answer: B. Earth spins on its axis once each day
Earth’s rotation on its axis makes the Sun appear to move across the sky once a day. Earth does orbit the Sun, but that takes a year, not a day.

5.A news story says a lunar eclipse will be visible tonight during the full moon. The Moon will look dark red for about an hour. A lunar eclipse happens when
1. A.Earth passes between the Sun and the Moon
2. B.the Sun passes between Earth and the Moon
3. C.the Moon moves into the shadow of Mars
4. D.the Moon passes between the Sun and Earth
Show answer
Answer: A. Earth passes between the Sun and the Moon
In a lunar eclipse, Earth blocks sunlight from reaching the Moon, so Earth’s shadow falls on it. When the Moon passes between the Sun and Earth, the result is a solar eclipse instead.

6.Iceland sits on the Mid-Atlantic Ridge. Measurements show the island is slowly widening by about 2 cm per year, and lava often erupts along long cracks in the ground. Which type of plate boundary runs through Iceland?
1. A.A convergent boundary where plates collide
2. B.A divergent boundary where plates move apart
3. C.A transform boundary where plates slide past
4. D.A boundary where one plate sinks under another
Show answer
Answer: B. A divergent boundary where plates move apart
Widening land and lava rising through cracks show plates pulling apart, which happens at a divergent boundary. Plates that collide or sink push crust together, which would not make the island wider.

7.A city adds curbside recycling for paper, glass and metal, so less of these materials goes to the landfill. What is the most direct benefit for natural resources?
1. A.It makes more fossil fuels form underground
2. B.It makes nonrenewable metals renewable
3. C.It reduces the need to mine and cut new materials
4. D.It increases the amount of rain each year
Show answer
Answer: C. It reduces the need to mine and cut new materials
Recycled paper, glass and metal replace some new raw materials, so less mining and logging are needed. Recycling does not make metals renewable; it only makes existing supplies last longer.

8.A hazard map shows that one neighborhood sits on loose, water-soaked sand, while another sits on solid bedrock. Both are the same distance from a fault. During a strong earthquake, which is most likely?
1. A.The sandy neighborhood will have more damage
2. B.Both neighborhoods will shake exactly the same
3. C.The bedrock neighborhood will shake the most
4. D.Neither neighborhood can be harmed by shaking
Show answer
Answer: A. The sandy neighborhood will have more damage
Loose, wet sand shakes more strongly and can even act like a liquid, so buildings on it suffer more damage. Being the same distance from the fault does not mean the same shaking, because the type of ground matters.

9.On a certain day, the Moon is located directly between Earth and the Sun. Which phase do people on Earth see?
1. A.First quarter, with half its face lit
2. B.New moon, with its lit side facing away
3. C.Full moon, with its lit side facing Earth
4. D.Lunar eclipse, with Earth’s shadow on it
Show answer
Answer: B. New moon, with its lit side facing away
When the Moon is between Earth and the Sun, its sunlit side faces away from us, so we see a new moon. A full moon happens when Earth is between the Sun and the Moon instead.

10.A geologist finds fossil seashells inside limestone near the top of a mountain far from any ocean. What is the best explanation?
1. A.The rock formed under a sea and was later pushed up
2. B.Birds carried the shells up and dropped them there
3. C.Seashells can grow on land if the air is moist enough
4. D.The mountain rose first, and the shells grew on it later
Show answer
Answer: A. The rock formed under a sea and was later pushed up
Limestone with shells forms on a sea floor, and plate movements can lift those layers into mountains over millions of years. Birds dropping shells would not explain shells built into the rock layers.

11.On a summer afternoon, the land near a lake heats up faster than the water. A cool breeze begins to blow from the lake toward the shore. Why does the breeze form?
1. A.The lake gives off cool wind as it evaporates
2. B.Warm air over land rises, and lake air moves in
3. C.Sunlight pushes the air from the lake to the land
4. D.Cold water pulls air down toward the lake
Show answer
Answer: B. Warm air over land rises, and lake air moves in
Warm air over the hotter land rises, and cooler, denser air from over the lake flows in to replace it. The idea that the lake gives off wind is tempting, but the breeze comes from uneven heating, not from the water itself.

12.Mercury is closer to the Sun than Venus, yet Venus has the hotter surface. Venus has a thick atmosphere made mostly of carbon dioxide, while Mercury has almost no atmosphere. What best explains why Venus is hotter?
1. A.Venus’s thick atmosphere traps heat near the surface
2. B.Mercury has more volcanoes cooling its surface
3. C.Venus spins faster, which creates heat by friction
4. D.Venus is larger, so it receives more sunlight
Show answer
Answer: A. Venus’s thick atmosphere traps heat near the surface
Venus’s dense carbon dioxide atmosphere causes a strong greenhouse effect that traps heat, so it is hotter than Mercury despite being farther from the Sun. Size is the tempting choice, but distance from the Sun matters far more than size for sunlight received.

13.A fire weather report lists conditions for a county: no rain for 40 days, humidity below 15% and wind gusts of 45 mph. Why do these conditions raise the wildfire risk?
1. A.Strong wind is what starts most of these wildfires on its own
2. B.Low humidity makes rain fall harder when it comes
3. C.Dry plants catch fire easily and wind spreads flames fast
4. D.Dry soil gives off gases that burst into flames
Show answer
Answer: C. Dry plants catch fire easily and wind spreads flames fast
Long dry spells and low humidity dry out grass and brush, and strong wind pushes flames and embers quickly. Wind alone does not start fires; it spreads them once dry fuel has been ignited.

14.A table compares four planets. Mars: rocky surface, density 3.9 g/cm³ Earth: rocky surface, density 5.5 g/cm³ Jupiter: no solid surface, density 1.3 g/cm³ Saturn: no solid surface, density 0.7 g/cm³ Which statement is best supported by the table?
1. A.Mars is the densest of the four planets listed
2. B.Saturn is denser than each of the other three planets
3. C.The rocky planets are farther from the Sun
4. D.The gas giants are less dense than the rocky planets
Show answer
Answer: D. The gas giants are less dense than the rocky planets
Jupiter and Saturn, which have no solid surface, have lower densities than Mars and Earth. Distance from the Sun is not given in the table, so that choice is not supported by it.

15.A fossil collector notices that nearly all fossils are found in sedimentary rocks, such as shale and limestone, and almost never in igneous rocks, such as granite. Which statement best explains this?
1. A.Fossils slowly turn into granite after long burial
2. B.Sedimentary rocks are always older than igneous rocks
3. C.Sediment buries remains gently, but magma destroys them
4. D.Igneous rocks form only where nothing has ever lived
Show answer
Answer: C. Sediment buries remains gently, but magma destroys them
Sediment settles over dead organisms and preserves their shapes as it hardens into rock, while molten rock would burn or melt remains. Sedimentary rocks are not always older; both rock types form at many different times.

16.On a summer afternoon, warm, moist air rises from a field. As it rises, it expands and cools, and puffy clouds form high above the field. What causes the clouds to form?
1. A.Cooling air turns liquid droplets into vapor
2. B.Rising air gathers dust that becomes water
3. C.Sunlight warms the vapor until it glows bright white
4. D.Cooling water vapor condenses into tiny droplets
Show answer
Answer: D. Cooling water vapor condenses into tiny droplets
Cooler air cannot hold as much water vapor, so the vapor condenses into the droplets that make up clouds. Turning droplets into vapor is evaporation, the opposite of what happens as rising air cools.

17.Quito, Ecuador, lies almost on the equator, yet its average daytime high is only about 19°C all year. The city sits about 2,850 m above sea level. Which factor best explains Quito’s mild temperatures?
1. A.Its distance from the nearest ocean
2. B.Its high elevation, since air cools with height
3. C.Earth’s tilt away from Ecuador all year
4. D.Its location far from the equator
Show answer
Answer: B. Its high elevation, since air cools with height
Air gets cooler with elevation, so Quito’s height keeps it mild despite strong equatorial sunlight. The passage says Quito is almost on the equator, so distance from the equator cannot explain it.

18.Each summer, a large area of the Gulf of Mexico has so little oxygen that fish leave or die. Scientists link it to fertilizer that washes from farms into the Mississippi River. The fertilizer feeds huge blooms of algae, and bacteria use up oxygen as they decompose the dead algae. Which action would most directly shrink this low-oxygen area?
1. A.Catching more fish so fewer need oxygen
2. B.Reducing fertilizer runoff from farms
3. C.Building dams to speed up river flow
4. D.Adding fertilizer to feed Gulf fish
Show answer
Answer: B. Reducing fertilizer runoff from farms
Less fertilizer reaching the Gulf means smaller algae blooms and less oxygen used up during decay. Catching more fish is tempting, but fish are not the cause; the oxygen is used by bacteria breaking down algae.

19.Scientists study air bubbles trapped in ancient Antarctic ice. Over the past 800,000 years, times with more carbon dioxide in the air also had higher average temperatures, and times with less carbon dioxide were colder. Why does this pattern matter for understanding today’s climate?
1. A.It links higher carbon dioxide with warmer climate
2. B.It proves the Sun has slowly grown dimmer over time
3. C.It shows ice cores cannot record past conditions
4. D.It shows that carbon dioxide levels never change
Show answer
Answer: A. It links higher carbon dioxide with warmer climate
The ice records show carbon dioxide and temperature rising and falling together, which fits carbon dioxide’s role as a heat-trapping gas. The claim that carbon dioxide never changes is contradicted by the record, since its level went up and down many times.

20.A climate report lists reasons that global sea level has risen over the past century. Which two causes does the scientific evidence support most strongly?
1. A.More rain falling on the ocean and fish growing larger
2. B.Floating sea ice melting and the Moon moving closer
3. C.Rivers carrying more sand and more ships at sea
4. D.Melting land ice and warming ocean water expanding
Show answer
Answer: D. Melting land ice and warming ocean water expanding
Water from melting glaciers and ice sheets on land adds to the ocean, and warmer water takes up more space. Melting floating sea ice is tempting, but that ice already displaces its own weight of water, so it adds very little.

21.A table compares four ways to make electricity. Coal: nonrenewable, releases CO₂ when used Natural gas: nonrenewable, releases CO₂ when used Nuclear: nonrenewable, releases almost no CO₂ when used Solar: renewable, releases almost no CO₂ when used Which source releases almost no CO₂ but depends on a fuel that will run out?
1. A.Coal
2. B.Natural gas
3. C.Nuclear
4. D.Solar
Show answer
Answer: C. Nuclear
Nuclear power uses uranium, a fuel that will run out, but it releases almost no CO₂ while making electricity. Solar also releases almost no CO₂, but it is renewable, so it does not fit.

22.A soil scientist reports that new topsoil forms at about 1 cm every 200 years. On one farm, plowing and wind remove about 1 cm of topsoil every 10 years. Which conclusion is best supported?
1. A.Topsoil is a renewable resource on this farm at any rate of use
2. B.The farm is losing topsoil far faster than it forms
3. C.Wind does not affect how fast topsoil is lost
4. D.The farm’s topsoil will grow thicker over time
Show answer
Answer: B. The farm is losing topsoil far faster than it forms
The farm loses 1 cm in 10 years but needs about 200 years to rebuild 1 cm, so loss is about 20 times faster than formation. Calling the soil renewable at any rate ignores that it is used up far faster than it forms.

23.After an earthquake, seismograph stations record two kinds of waves. P waves travel about 6 km per second, and S waves travel about 3.5 km per second. At one station, the S waves arrived 50 seconds after the P waves. What can scientists learn from this time gap?
1. A.How far the station is from the earthquake’s source
2. B.Which tectonic plate will move next in the region
3. C.The exact day the next earthquake will strike there
4. D.How many aftershocks will follow the main earthquake
Show answer
Answer: A. How far the station is from the earthquake’s source
The farther the waves travel, the more the slower S waves fall behind, so the time gap tells the distance to the source. Scientists cannot predict the exact day of an earthquake, so that choice goes beyond what seismographs can do.

24.Craters from meteor impacts billions of years ago can still be seen on the Moon. On Earth, most ancient impact craters have disappeared. Which difference best explains this?
1. A.The Moon’s craters are kept fresh by its tides
2. B.The Moon is larger than Earth, so its craters last
3. C.The Moon lacks the wind and water that erode craters
4. D.Earth’s craters were filled in by the Moon’s gravity
Show answer
Answer: C. The Moon lacks the wind and water that erode craters
Earth’s wind, water, plants and moving plates wear down and bury old craters, while the Moon has almost no air or liquid water to erode them. The Moon is smaller than Earth, so size cannot explain the difference.

25.The Sun is far more massive than the Moon, yet the Moon has a larger effect on Earth’s ocean tides. Why?
1. A.The Moon gives off its own light
2. B.The Moon has more water on its surface
3. C.The Moon has a stronger magnetic field
4. D.The Moon is much closer to Earth
Show answer
Answer: D. The Moon is much closer to Earth
Tides depend on how much gravity changes from one side of Earth to the other, and that effect grows quickly as distance shrinks, so the nearby Moon wins. The Moon does not make its own light; it reflects sunlight.

26.On a clear night, a full moon is bright enough to cast shadows on the ground. Where does the Moon’s light come from?
1. A.Sunlight reflected off the Moon
2. B.Light from Earth’s cities at night
3. C.Glowing rock from the Moon’s core
4. D.Hot gases burning on the Moon
Show answer
Answer: A. Sunlight reflected off the Moon
The Moon makes no light of its own; it shines by reflecting sunlight. City light is far too weak to light up the Moon, which is why the Moon looks bright even over dark oceans.

27.Lava pours from a volcano into the sea and cools within minutes. The rock that forms has tiny crystals that can be seen only with a magnifier. Why are the crystals so small?
1. A.The rock formed from layers of sand
2. B.The seawater added salt crystals to it
3. C.The rock was squeezed by great pressure
4. D.The lava cooled too fast to grow crystals
Show answer
Answer: D. The lava cooled too fast to grow crystals
Crystals need time to grow, so lava that cools in minutes forms igneous rock with very small crystals. Layers of sand would make sedimentary rock, which is not formed from lava.

28.A fossil guide notes that fossils of clams, snails and bones are common, but fossils of jellyfish and worms are very rare, even though these animals have lived in the oceans for hundreds of millions of years. What best explains the difference?
1. A.Jellyfish and worms lived only on dry land
2. B.Jellyfish and worms appeared on Earth recently
3. C.Hard shells dissolve faster than soft tissues
4. D.Soft body parts usually decay before fossilizing
Show answer
Answer: D. Soft body parts usually decay before fossilizing
Hard parts such as shells and bones last long enough to be buried and preserved, while soft bodies usually rot away first. The passage says these animals have lived in the oceans for hundreds of millions of years, so they are not recent or land animals.

29.Along the San Andreas Fault in California, the Pacific Plate and the North American Plate grind sideways past each other. Earthquakes are common there, but volcanoes are not. What type of plate boundary is this?
1. A.A divergent boundary
2. B.A transform boundary
3. C.A convergent boundary
4. D.A hot spot boundary
Show answer
Answer: B. A transform boundary
At a transform boundary, plates slide horizontally past each other, which causes earthquakes but little volcanic activity. A divergent boundary has plates moving apart, often with volcanoes, which does not match.

30.GPS stations show that a tectonic plate is moving at about 5 cm per year. (100,000 cm = 1 km) About how far will the plate move in 1 million years?
1. A.0.5 km
2. B.5 km
3. C.50 km
4. D.500 km
Show answer
Answer: C. 50 km
Multiply 5 cm by 1,000,000 years to get 5,000,000 cm, then divide by 100,000 to get 50 km. Choosing 5 km comes from dropping one zero during the conversion.

Earth's structure and rock layers on the GED

Earth has four layers: crust, mantle, liquid outer core, and solid inner core. The circulating molten metal of the outer core generates the planet's magnetic field. Tectonic plates float on the mantle, and earthquakes, volcanoes, and mountain ranges concentrate at their boundaries.

In undisturbed sedimentary layers, newer material sits on top of older material. This principle of superposition lets geologists read a sequence of events out of a cliff face, and it is a favorite setup for GED diagram questions.

Water, weather, and climate on the GED Science test

The water cycle moves through evaporation, condensation, precipitation, and collection, with transpiration from plants and infiltration into soil as additional paths. Weather questions usually involve air masses: when a cold front pushes under warmer air, the warm air rises, cools, condenses, and produces clouds and storms.

Climate questions center on greenhouse gases. Carbon dioxide and methane trap outgoing infrared energy, and rising concentrations correlate with rising global average temperature. Expect to interpret a graph rather than recall a number.

Natural resources and space science on the GED

Renewable resources such as wind, solar, and hydro replenish on a human timescale. Fossil fuels do not. Questions often ask you to weigh a tradeoff rather than declare one option best.

For space, the essentials are short: Earth's seasons come from its axial tilt, not its distance from the Sun; moons orbit planets while planets orbit stars; and the phases of the Moon result from the changing angle of sunlight we see from Earth.

Frequently asked questions

How much earth science is on the GED?: Earth and space science is about 20 percent of the Science test.
What causes the seasons?: Earth's roughly 23.5-degree axial tilt, which changes how directly sunlight strikes each hemisphere through the year.