General Science
Earth & Space Science
Earth and space science covers processes shaping our planet and objects beyond it. Focus on major structures, processes, cause and effect, and basic solar-system knowledge: layers, plates, rocks, weather, oceans, rotation, the Moon, eclipses, planets, and stars.
Section 1
Earth's Layers & Plate Tectonics
Earth has a thin outer crust, a much thicker mantle, a liquid outer core, and a solid inner core. Movement of liquid iron and nickel in the outer core helps generate Earth's magnetic field.
Earth's outer rigid layer is broken into tectonic plates that move slowly. At divergent boundaries plates move apart and new crust can form. At convergent boundaries plates move together. At transform boundaries plates slide past one another, often causing earthquakes.
Example 1
Which Earth layer is liquid and helps generate the magnetic field? A. Crust | B. Mantle | C. Outer core | D. Inner core
Solution
- 1The outer core contains moving liquid iron and nickel.
Why: Movement of conductive liquid metal in the outer core helps generate Earth's magnetic field.
Example 2
At which plate boundary do two plates move apart? A. Convergent | B. Divergent | C. Transform | D. Stationary
Solution
- 1Divergent means moving away from one another.
Why: At divergent boundaries, plates separate and new crust may form.
Section 2
Earthquakes & Volcanoes
Earthquakes occur when stored energy in Earth's crust is suddenly released as rocks break or slip along faults. A volcano is an opening through which molten rock, gases, and other materials escape.
A fault is a break in Earth's crust where movement occurs. The focus is where an earthquake begins underground; the epicenter is the surface point directly above it. Magma is molten rock below ground, while lava is molten rock at the surface. Volcanoes commonly form near convergent boundaries, divergent boundaries, and some hot spots.
Example 1
What is the point on Earth's surface directly above an earthquake's focus? A. Fault | B. Epicenter | C. Mantle | D. Crater
Solution
- 1The earthquake begins underground at the focus.
- 2The surface point directly above it is the epicenter.
Why: The epicenter identifies the surface location above the earthquake's starting point.
Example 2
What is molten rock called while it is beneath Earth's surface? A. Lava | B. Magma | C. Sediment | D. Mineral
Solution
- 1Below the surface, molten rock is magma. Once it reaches the surface, it is lava.
Why: Magma and lava describe molten rock in different locations.
Section 3
Minerals, Rocks & the Rock Cycle
Minerals are naturally occurring inorganic solids with characteristic composition and structure. They are building blocks of many rocks. The three major rock types are igneous, sedimentary, and metamorphic.
Igneous rock forms when magma or lava cools and solidifies. Sedimentary rock forms from deposited, compacted, and cemented sediments. Metamorphic rock forms when existing rock is changed by heat and pressure without fully melting. The rock cycle changes rocks between types over time.
Example 1
Which rock forms when magma or lava cools and solidifies? A. Sedimentary | B. Igneous | C. Metamorphic | D. Mineral
Solution
- 1Cooling molten rock forms igneous rock.
Why: Igneous rocks form directly from cooled magma or lava.
Example 2
A rock changes by intense heat and pressure but does not melt. What type forms? A. Igneous | B. Metamorphic | C. Sedimentary | D. Liquid rock
Solution
- 1Heat and pressure can transform existing rock without melting it.
Why: Metamorphic rocks form when existing rocks are altered by heat and pressure.
Example 3
Which rock commonly forms from compacted and cemented sediments? A. Sedimentary | B. Igneous | C. Magma | D. Outer-core rock
Solution
- 1Layers of sediment can become compacted and cemented together.
Why: Sedimentary rocks commonly form from accumulated sediments.
Section 4
Weathering, Erosion & the Water Cycle
Weathering breaks rock into smaller pieces; erosion moves weathered material using water, wind, ice, or gravity. Weathering means breaking down, while erosion means moving away.
Physical weathering breaks rock without changing composition, such as freezing and thawing, roots cracking rock, and abrasion. Chemical weathering changes mineral composition. The water cycle includes evaporation (liquid → gas), condensation (gas → liquid), precipitation, runoff, and infiltration.
Example 1
Water freezes in a rock crack, expands, and repeatedly widens it. This is: A. Physical weathering | B. Chemical bonding | C. Condensation | D. Plate convergence
Solution
- 1The rock is physically broken apart without needing a chemical change.
Why: Freeze-thaw cycles mechanically break rock into smaller pieces.
Example 2
What is the difference between weathering and erosion? A. Weathering moves sediment. | B. Weathering breaks down while erosion transports. | C. They are identical. | D. Erosion only occurs underground.
Solution
- 1Weathering breaks material apart.
- 2Erosion moves the material elsewhere.
Why: Breaking and transporting are different parts of the process.
Example 3
What changes liquid water into water vapor? A. Condensation | B. Precipitation | C. Evaporation | D. Runoff
Solution
- 1Liquid water gains enough energy for molecules to escape as vapor.
Why: Evaporation is the liquid-to-gas part of the water cycle.
Section 5
Atmosphere & Weather
Earth's atmosphere is a layer of gases, mostly nitrogen followed by oxygen. The troposphere is its lowest major layer and is where most weather occurs.
Weather is short-term atmospheric conditions, while climate is long-term patterns. Air pressure differences help create wind. Warm air is generally less dense and tends to rise; cool air tends to sink. Clouds form when water vapor cools and condenses into tiny droplets or ice crystals.
Example 1
In which atmospheric layer does most weather occur? A. Troposphere | B. Inner core | C. Mantle | D. Outer core
Solution
- 1The troposphere is Earth's lowest major atmospheric layer.
Why: It contains much of the atmosphere's water vapor and weather activity.
Example 2
Which statement describes climate? A. Today's noon temperature | B. Long-term weather patterns in an area | C. A single storm | D. Current wind speed
Solution
- 1Climate describes patterns over long periods.
Why: Weather is short-term; climate describes typical conditions over many years.
Example 3
Why does warm air generally rise above cooler air? A. It is less dense. | B. It has no molecules. | C. Gravity stops affecting it. | D. It becomes solid.
Solution
- 1Heating air makes it expand and become less dense.
Why: Less-dense warm air rises while denser cool air sinks.
Section 6
Oceans & Currents
Oceans cover most of Earth's surface and influence climate, weather, the water cycle, and ecosystems. Ocean water is salty because it contains dissolved salts.
Surface currents are strongly influenced by wind, Earth's rotation, and continents. Deep currents are influenced by temperature, salinity, and density; cold salty water is denser than warm, less-salty water. Most surface waves are caused by wind. Tides are regular water-level changes mainly caused by the Moon's gravity.
Example 1
What primarily causes most surface ocean waves? A. Wind | B. Earth's inner core | C. Volcanoes only | D. Magnetic fields
Solution
- 1Wind transfers energy to the water surface.
Why: Most ordinary surface waves begin with wind across the ocean.
Example 2
What can help drive deep ocean currents? A. Differences in water density | B. Only cloud cover | C. Moon phases alone | D. Crust thickness
Solution
- 1Temperature and salinity affect density.
- 2Density differences help drive deep currents.
Why: Denser water can sink while less-dense water rises or remains above it.
Example 3
Which object most influences Earth's ocean tides? A. Mars | B. Moon | C. Jupiter | D. Venus
Solution
- 1The Moon's gravity strongly affects Earth’s oceans.
Why: The Moon is close to Earth and is the primary driver of tides.
Section 7
Earth's Rotation, Revolution & the Moon
Rotation is Earth spinning on its axis every 24 hours and causes day and night. Revolution is Earth's orbit around the Sun, about 365 days, and defines a year.
Seasons are caused mainly by Earth's axial tilt combined with revolution, not changing Earth-Sun distance. The Moon orbits Earth and its phases occur because we see different portions of its sunlit half. The Moon reflects sunlight rather than producing visible light of its own.
Example 1
What causes day and night on Earth? A. Revolution | B. Rotation | C. Moon's orbit | D. Ocean currents
Solution
- 1As Earth rotates, different parts face toward and away from the Sun.
Why: One rotation takes about 24 hours and produces the daily light-dark cycle.
Example 2
What is the primary reason Earth experiences seasons? A. Changing distance from Sun | B. Axial tilt while revolving | C. Moon blocking sunlight | D. Tides
Solution
- 1Earth's tilted axis gives each hemisphere different sunlight angles and durations as it revolves.
Why: Tilt changes the amount and angle of sunlight received during the year.
Example 3
Why does the Moon appear to change shape during a month? A. Earth shadow covers it nightly. | B. It changes shape. | C. We see different portions of its sunlit half. | D. It produces different light amounts.
Solution
- 1The Moon is always roughly half illuminated by the Sun.
- 2Its orbit changes how much of that lit half we see.
Why: Moon phases result from changing positions of Sun, Earth, and Moon.
Section 8
Eclipses, Planets & the Solar System
A solar eclipse occurs when the Moon is between the Sun and Earth: Sun → Moon → Earth. A lunar eclipse occurs when Earth is between the Sun and Moon: Sun → Earth → Moon.
The solar system includes the Sun, eight planets, dwarf planets, moons, asteroids, comets, and smaller objects. Inner rocky planets are Mercury, Venus, Earth, and Mars. Outer planets are Jupiter, Saturn, Uranus, and Neptune. The Sun is a star at the system's center, and gravity keeps planets in orbit.
Example 1
What arrangement occurs during a solar eclipse? A. Sun → Earth → Moon | B. Earth → Sun → Moon | C. Sun → Moon → Earth | D. Moon → Earth → Sun
Solution
- 1The Moon must be between Earth and Sun to block sunlight.
Why: The Moon passes between Earth and the Sun during a solar eclipse.
Example 2
Which planet is closest to the Sun? A. Venus | B. Earth | C. Mercury | D. Mars
Solution
- 1The planet order begins Mercury, Venus, Earth, Mars.
Why: Mercury is the first planet from the Sun.
Example 3
What keeps Earth in orbit around the Sun? A. Sound waves | B. Gravity | C. Ocean currents | D. Earth's magnetic field alone
Solution
- 1The Sun's gravity pulls Earth inward while Earth moves forward through space.
Why: Gravity supplies the inward force that maintains Earth's orbit.
Quick Review
Quick Review
- Crust is outer layer; mantle is thick middle; outer core liquid; inner core solid. Divergent plates move apart, convergent move together, transform slide past.
- Igneous rock is cooled molten rock; sedimentary rock comes from compacted sediments; metamorphic rock comes from heat and pressure. Weathering breaks down; erosion moves.
- Troposphere has most weather. Surface currents are wind-driven; deep currents reflect density differences; tides are mainly caused by the Moon.
- Earth rotation creates day/night; revolution defines year; axial tilt plus revolution creates seasons. Solar eclipse: Sun → Moon → Earth; lunar eclipse: Sun → Earth → Moon.
The Big Picture
- Plate movement → earthquakes, volcanoes, and mountains. Molten rock cools → igneous rock. Evaporation moves water into atmosphere; condensation forms clouds. Wind drives surface currents. Moon gravity causes tides. Earth rotation → day/night. Gravity keeps planets in orbit.