GED Science 2 — Questions and Answers

Question 1: Which layer of Earth's atmosphere is responsible for absorbing most of the sun's ultraviolet (UV) radiation?

Troposphere
Stratosphere (Correct answer)
Mesosphere
Thermosphere

Correct answer: Stratosphere

The stratosphere contains the ozone layer, which absorbs 97-99% of the sun's harmful ultraviolet radiation, protecting life on Earth.

Earth's atmosphere has five main layers (from surface outward): 1. Troposphere (0–12 km): where weather occurs; temperature decreases with altitude 2. Stratosphere (12–50 km): contains ozone layer; temperature increases with altitude due to UV absorption 3. Mesosphere (50–80 km): coldest layer; meteors burn up here 4. Thermosphere (80–700 km): very hot; auroras occur; ISS orbits here 5. Exosphere: outermost layer; transitions to space The ozone layer (mainly 15–35 km altitude) contains ozone (O₃) molecules that absorb UV-B and UV-C radiation from the sun. Without this protection, UV radiation would cause skin cancer, cataracts, and damage to plant and marine life. Human-produced chemicals called CFCs (chlorofluorocarbons) have depleted the ozone layer, particularly over Antarctica, creating the 'ozone hole.' The Montreal Protocol (1987) banned CFCs, and the ozone layer is slowly recovering.

Question 2: What causes the seasons on Earth?

Earth's varying distance from the Sun throughout the year
The tilt of Earth's axis relative to its orbit around the Sun (Correct answer)
The rotation of Earth on its axis every 24 hours
Sunspot activity on the surface of the Sun

Correct answer: The tilt of Earth's axis relative to its orbit around the Sun

Earth's 23.5° axial tilt causes seasons. When the Northern Hemisphere is tilted toward the Sun, it experiences summer; when tilted away, it experiences winter.

Earth's seasons are caused by the 23.5° tilt of Earth's axis relative to its orbital plane around the Sun, NOT by Earth's distance from the Sun. How the tilt causes seasons: • When the Northern Hemisphere tilts TOWARD the Sun (summer): receives more direct sunlight, longer days → warmer temperatures • When the Northern Hemisphere tilts AWAY from the Sun (winter): receives less direct sunlight, shorter days → colder temperatures Key dates: • Summer solstice (June 21): Northern Hemisphere most tilted toward Sun, longest day of year • Winter solstice (December 21): Northern Hemisphere most tilted away, shortest day • Equinoxes (March 20, September 23): equal day and night (12 hours each) Note: Earth is actually CLOSEST to the Sun in January (Northern Hemisphere winter) — proving distance is not the cause of seasons. The Southern Hemisphere experiences opposite seasons.

Question 3: The rock cycle includes three main rock types. Which of the following correctly describes how igneous rock forms?

From layers of sediment that are compacted and cemented over time
From pre-existing rocks that are changed by heat and pressure
From molten magma that cools and solidifies (Correct answer)
From organisms that die and accumulate on the ocean floor

Correct answer: From molten magma that cools and solidifies

Igneous rock forms when molten rock (magma underground, lava at the surface) cools and solidifies. Examples include granite and basalt.

The rock cycle describes how rocks transform from one type to another over millions of years. Three main rock types: 1. Igneous rock: forms from cooling and solidification of molten rock (magma/lava) • Intrusive (plutonic): magma cools slowly underground → large crystals (e.g., granite) • Extrusive (volcanic): lava cools quickly at surface → small crystals or glassy texture (e.g., basalt, obsidian) 2. Sedimentary rock: forms from compaction and cementation of sediment layers • Examples: sandstone, limestone, shale • Contains fossils 3. Metamorphic rock: forms when existing rocks are transformed by intense heat and/or pressure • Examples: marble (from limestone), slate (from shale), quartzite (from sandstone) Rock cycle transformations: • Igneous → Sedimentary (via weathering, erosion, deposition) • Sedimentary → Metamorphic (via heat and pressure) • Metamorphic → Igneous (via melting)

Question 4: What evidence best supports the theory of plate tectonics?

The Sun's gravitational pull on Earth
The complementary shapes of continents and matching fossils across oceans (Correct answer)
The daily rising and setting of the Sun
The tides in Earth's oceans

Correct answer: The complementary shapes of continents and matching fossils across oceans

The matching coastlines of continents (like South America and Africa), identical fossils on opposite sides of oceans, and similar rock formations provide strong evidence that continents were once joined.

Plate tectonics is the theory that Earth's lithosphere is divided into plates that move slowly over the mantle. Evidence includes: 1. Continental fit: South America and Africa coastlines fit together like puzzle pieces 2. Fossil evidence: identical fossils of the same ancient species (e.g., Mesosaurus, Glossopteris) found on continents now separated by oceans 3. Rock formations: similar rock layers and mountain ranges that line up across continents (Appalachian Mountains match mountains in Scotland and Norway) 4. Paleoclimate evidence: coal deposits (from tropical forests) in Antarctica, glacial deposits in tropical Africa 5. Seafloor spreading: magnetic striping patterns symmetric on both sides of mid-ocean ridges 6. Earthquake and volcano distribution: occur in predictable patterns at plate boundaries Alfred Wegener proposed 'continental drift' in 1912, but the mechanism (seafloor spreading) wasn't understood until the 1960s.

Question 5: Which phase of the Moon occurs when the Moon is between Earth and the Sun?

Full Moon
New Moon (Correct answer)
First Quarter
Last Quarter

Correct answer: New Moon

During a New Moon, the Moon is between Earth and the Sun. The Sun illuminates the far side of the Moon, so from Earth, the Moon appears dark (not visible).

The Moon's phases result from changes in the Moon's position relative to Earth and the Sun. New Moon: Moon is between Earth and Sun → lit side faces the Sun (away from Earth) → Moon appears dark from Earth. This is when solar eclipses can occur. Full Moon: Earth is between Moon and Sun → entire lit side faces Earth → Moon appears fully illuminated. This is when lunar eclipses can occur. The Moon's cycle (synodic period) takes approximately 29.5 days: New Moon → Waxing Crescent → First Quarter → Waxing Gibbous → Full Moon → Waning Gibbous → Last Quarter → Waning Crescent → New Moon 'Waxing' means the visible portion is growing; 'waning' means it's shrinking. The same side of the Moon always faces Earth (synchronous rotation) — the Moon rotates once on its axis for every orbit around Earth.

Question 6: What is the greenhouse effect, and how does it affect Earth's temperature?

It cools Earth by reflecting sunlight back into space
It warms Earth by trapping heat in the atmosphere (Correct answer)
It creates precipitation by condensing water vapor
It blocks UV rays from reaching Earth's surface

Correct answer: It warms Earth by trapping heat in the atmosphere

Greenhouse gases (CO₂, water vapor, methane) trap infrared radiation emitted by Earth's surface, warming the atmosphere — like glass in a greenhouse.

The greenhouse effect is a natural process that warms Earth's surface to livable temperatures: How it works: 1. Sunlight (short-wave radiation) passes through the atmosphere and warms Earth's surface 2. Earth's surface emits heat as infrared (long-wave) radiation 3. Greenhouse gases (CO₂, H₂O vapor, CH₄, N₂O, ozone) absorb this infrared radiation 4. These gases re-emit heat in all directions, including back toward Earth 5. This 'trapping' raises Earth's surface temperature The natural greenhouse effect is ESSENTIAL — without it, Earth's average temperature would be about −18°C (0°F) instead of the current +15°C (59°F). The ENHANCED greenhouse effect refers to human activities (burning fossil fuels, deforestation) increasing CO₂ and other greenhouse gases, intensifying warming beyond natural levels — this is climate change. Note: The stratospheric ozone layer (which blocks UV) is a separate phenomenon from the greenhouse effect.

GED Science 2

Which layer of Earth's atmosphere is responsible for absorbing most of the sun's ultraviolet (UV) radiation?