AFCT General Science: Earth and Space 2 — Questions and Answers

Question 1: What causes the seasons on Earth?

Changes in Earth's distance from the Sun
The tilt of Earth's axis at 23.5 degrees relative to its orbital plane (Correct answer)
Variations in the Sun's energy output
The Moon's gravitational pull on Earth

Correct answer: The tilt of Earth's axis at 23.5 degrees relative to its orbital plane

Earth's seasons result from the 23.5-degree tilt of its rotational axis. As Earth orbits the Sun, different hemispheres receive more direct sunlight at different times of year, creating seasons.

Earth's rotational axis is tilted 23.5 degrees from perpendicular to its orbital plane (the ecliptic). This tilt means that as Earth orbits the Sun, the Northern and Southern Hemispheres alternate between being tilted toward and away from the Sun. When a hemisphere tilts toward the Sun, it receives more direct sunlight (higher solar angle) and longer days, creating summer. When tilted away, sunlight strikes at a lower angle and days are shorter, creating winter. Earth's distance from the Sun varies by only about 3% and actually places Earth closest to the Sun (perihelion) in early January, during Northern Hemisphere winter. This demonstrates that distance is not the cause of seasons. The equinoxes (March and September) occur when neither hemisphere tilts toward the Sun.

Question 2: What type of rock is formed from cooled and solidified magma or lava?

Sedimentary rock
Metamorphic rock
Igneous rock (Correct answer)
Composite rock

Correct answer: Igneous rock

Igneous rocks form when molten rock (magma underground or lava at the surface) cools and crystallizes. Examples include granite (intrusive/slow cooling) and basalt (extrusive/fast cooling).

Igneous rocks are one of the three main rock types in the rock cycle. They form in two settings: intrusive (plutonic) rocks crystallize slowly deep underground from magma, producing large crystals visible to the naked eye (e.g., granite, gabbro, diorite). Extrusive (volcanic) rocks form when lava erupts at the surface and cools quickly, producing fine-grained or glassy textures (e.g., basalt, obsidian, pumice). The mineral composition depends on the magma's chemistry: felsic magmas (high silica) produce lighter-colored rocks like granite and rhyolite, while mafic magmas (low silica, high iron/magnesium) produce darker rocks like basalt and gabbro. Igneous rocks make up about 95% of the upper part of Earth's crust by volume.

Question 3: What is the main composition of the Sun?

Iron and nickel
Carbon and oxygen
Hydrogen and helium (Correct answer)
Nitrogen and argon

Correct answer: Hydrogen and helium

The Sun is composed of approximately 73% hydrogen and 25% helium by mass, with the remaining 2% being heavier elements. Nuclear fusion in the core converts hydrogen into helium, producing the Sun's energy.

The Sun is a main-sequence G-type star composed primarily of hydrogen (about 73% by mass) and helium (about 25%), with trace amounts of heavier elements like oxygen, carbon, iron, and neon. In the core, where temperatures reach about 15 million degrees Celsius and pressure is 250 billion atmospheres, hydrogen nuclei fuse through the proton-proton chain reaction to form helium. This process converts about 4 million tons of mass into energy every second via Einstein's E=mc². The energy produced takes tens of thousands of years to travel from the core through the radiative zone to the convective zone, eventually reaching the photosphere (visible surface at about 5,500°C). The Sun has been fusing hydrogen for approximately 4.6 billion years and has enough fuel for another 5 billion years.

Question 4: What layer of Earth's atmosphere contains the ozone layer that protects life from harmful UV radiation?

Troposphere
Stratosphere (Correct answer)
Mesosphere
Thermosphere

Correct answer: Stratosphere

The ozone layer is found in the stratosphere, roughly 15-35 km above Earth's surface. Ozone (O3) molecules absorb most of the Sun's harmful ultraviolet-B and ultraviolet-C radiation.

Earth's atmosphere has five main layers: troposphere (0-12 km, where weather occurs), stratosphere (12-50 km), mesosphere (50-80 km), thermosphere (80-700 km), and exosphere (700+ km). The ozone layer resides in the stratosphere, concentrated between 15-35 km altitude. Ozone (O3) is formed when UV radiation splits O2 molecules, and the freed oxygen atoms combine with other O2 molecules. This ozone-oxygen cycle continuously absorbs UV-B and UV-C radiation, which would otherwise cause skin cancer, cataracts, and ecosystem damage. The stratosphere actually warms with altitude due to ozone absorbing UV energy. Human-produced chlorofluorocarbons (CFCs) catalytically destroy ozone, leading to the Antarctic ozone hole discovered in the 1980s. The Montreal Protocol (1987) phased out CFCs, and the ozone layer is slowly recovering.

Question 5: What drives the movement of tectonic plates on Earth?

The Moon's gravitational force
Wind erosion on the surface
Convection currents in the mantle (Correct answer)
Earth's magnetic field

Correct answer: Convection currents in the mantle

Tectonic plates are driven primarily by convection currents in Earth's mantle. Heat from the core causes mantle rock to slowly circulate, with hotter material rising and cooler material sinking, dragging plates along.

Plate tectonics is driven by several mechanisms, with mantle convection being the primary force. Earth's interior heat (from radioactive decay and residual formation heat) creates temperature differences in the mantle. Hot, less dense rock rises from near the core, while cooler, denser rock near the surface sinks, creating convection cells. Additional driving forces include ridge push (elevated mid-ocean ridges push plates apart by gravity) and slab pull (dense oceanic lithosphere subducting into the mantle pulls the rest of the plate). The asthenosphere, a partially molten zone of the upper mantle, allows rigid lithospheric plates to slide over it. Plate interactions at boundaries create earthquakes, volcanoes, and mountain ranges: divergent boundaries (plates separate), convergent boundaries (plates collide), and transform boundaries (plates slide past each other).

Question 6: What is a light-year a measure of?

Time
Brightness
Distance (Correct answer)
Speed

Correct answer: Distance

A light-year is a unit of distance, not time. It is the distance that light travels in one year in a vacuum, approximately 9.46 trillion kilometers (5.88 trillion miles).

A light-year equals approximately 9.461 × 10^12 kilometers (5.879 × 10^12 miles). Light travels at approximately 299,792 km/s in a vacuum. Over one year, this amounts to nearly 9.5 trillion km. Astronomers use light-years to express the vast distances in space because using kilometers would result in unwieldy numbers. For example, the nearest star system (Alpha Centauri) is about 4.37 light-years away, meaning the light we see from it left over 4 years ago. The Milky Way galaxy is about 100,000 light-years across. Other distance units used in astronomy include the astronomical unit (AU, the Earth-Sun distance of about 150 million km, useful for solar system scales) and the parsec (3.26 light-years, based on stellar parallax measurements, preferred in professional astronomy).

AFCT General Science: Earth and Space 2

What causes the seasons on Earth?