Earth and Space Science: Practice Questions & Explanations

Order from Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Mnemonics: 'My Very Educated Mother Just Served Us Noodles' (replacing 'Nachos' since Pluto's reclassification). Pluto was reclassified as a dwarf planet in 2006. Planet categories: (1) Terrestrial (inner, rocky): Mercury, Venus, Earth, Mars — smaller, rocky surface, fewer or no moons, no rings; (2) Gas giants: Jupiter, Saturn — large, mostly hydrogen and helium, many moons, rings (Saturn most prominent); (3) Ice giants: Uranus, Neptune — large but smaller than gas giants, contain water/ammonia/methane ices, also have rings and many moons. Asteroid belt between Mars and Jupiter. Kuiper belt beyond Neptune (where Pluto resides). Key planet facts: Mercury — smallest, closest to Sun, extreme temperatures; Venus — hottest (runaway greenhouse), backwards rotation, brightest planet; Earth — only known life, liquid water; Mars — red from iron oxide, evidence of past water; Jupiter — largest, Great Red Spot, 95 moons; Saturn — most prominent rings, second largest, 146 moons; Uranus — tilted on side, rotates 'sideways'; Neptune — windiest, blue from methane. Sun is a yellow dwarf star; solar system formed ~4.6 billion years ago.

The rock cycle describes how Earth's rocks continually transform. Three rock types: (1) IGNEOUS — formed when molten rock (magma below ground, lava above) cools and solidifies. Intrusive igneous rocks cool slowly underground (granite, gabbro); extrusive cool quickly above (basalt, obsidian, pumice). (2) SEDIMENTARY — formed from accumulated sediments (weathered rock fragments, organic material, mineral precipitates) compressed and cemented over time. Examples: sandstone, limestone, shale, coal. Often layered and may contain fossils. (3) METAMORPHIC — formed when existing rocks are altered by heat, pressure, or chemical activity without melting. Examples: marble (from limestone), slate (from shale), gneiss (from granite or sedimentary), quartzite (from sandstone). Rock cycle transformations: igneous can weather/erode to sediment → sedimentary; sedimentary can be buried and metamorphosed → metamorphic; metamorphic can be uplifted and weathered → sediment → sedimentary; any rock can melt → magma → cool → igneous. Driving forces: plate tectonics (provides heat, pressure, uplift); weathering and erosion (breaks down rocks); volcanism (creates new igneous rock). Time scales: millions to billions of years.

Earth's seasons are caused by the 23.5° tilt of Earth's rotational axis relative to its orbital plane around the Sun. As Earth orbits, the tilt causes hemispheres to receive different amounts of direct sunlight at different times of year. Summer in a hemisphere: that hemisphere is tilted TOWARD the Sun, receiving more direct sunlight (higher in sky) and longer days. Winter: tilted AWAY from the Sun, less direct sunlight (lower in sky) and shorter days. Common misconception: many people think Earth's distance from Sun causes seasons. Earth's orbit is slightly elliptical, but the distance variation is small (~3%); Earth is actually CLOSEST to Sun in January (Northern winter) — proving distance doesn't cause seasons. Key dates: (1) March 20-21: Vernal Equinox — equal day/night globally; Northern spring begins, Southern fall begins; (2) June 20-21: Summer Solstice — longest day in Northern Hemisphere, shortest in Southern; (3) September 22-23: Autumnal Equinox; (4) December 21-22: Winter Solstice — shortest day in Northern, longest in Southern. At equator, less seasonal variation. Polar regions: 24 hours daylight in summer (midnight sun), 24 hours darkness in winter. Tropics of Cancer (23.5° N) and Capricorn (23.5° S) mark where Sun is directly overhead at solstices.

Earth's atmosphere composition: nitrogen (N₂) ~78%; oxygen (O₂) ~21%; argon (Ar) ~0.9%; carbon dioxide (CO₂) ~0.04% (rising due to fossil fuels); water vapor variable (0-4%); trace gases (neon, helium, methane, krypton, hydrogen, ozone). Important: oxygen is only 21% — but it's enough to sustain life. Atmospheric layers (low to high): (1) Troposphere — 0-12 km; weather happens here; temperature decreases with altitude; (2) Stratosphere — 12-50 km; contains ozone layer (absorbs UV); temperature increases with altitude; (3) Mesosphere — 50-85 km; meteors burn up; coldest layer; (4) Thermosphere — 85-600 km; auroras occur; very low density but high temperatures; (5) Exosphere — beyond, gradually merges with space. Greenhouse effect: certain gases (CO₂, methane, water vapor) absorb infrared radiation, trapping heat; natural greenhouse effect makes Earth habitable; human enhancement is causing climate change. Ozone layer protects against UV-B radiation; depleted by CFCs (now banned under Montreal Protocol). Air pressure decreases with altitude. Atmospheric pressure at sea level: ~1 atm ≈ 101 kPa ≈ 14.7 psi.

Plate tectonics is the unifying theory of Earth's geological processes. Earth's lithosphere (crust + upper mantle) is broken into ~15 major plates (and many smaller ones) that move slowly (cm/year) over the asthenosphere (semi-fluid upper mantle). Plate boundary types: (1) DIVERGENT — plates move apart; new crust forms; mid-ocean ridges (e.g., Mid-Atlantic Ridge); continental rifts (e.g., East African Rift); produces shallow earthquakes and basaltic volcanism; (2) CONVERGENT — plates collide; types depend on what collides: (a) oceanic-oceanic: subduction zone, volcanic island arcs (e.g., Japan, Aleutians); (b) oceanic-continental: subduction, coastal mountain ranges with volcanoes (e.g., Andes, Cascades); (c) continental-continental: mountain building, no subduction (e.g., Himalayas formed by India-Asia collision); produces deep earthquakes and explosive volcanism; (3) TRANSFORM — plates slide past each other; major earthquakes (e.g., San Andreas Fault in California). Evidence for plate tectonics: (1) Continental jigsaw fit (Africa-South America); (2) Matching fossils across continents; (3) Matching rock formations and ages; (4) Mid-ocean ridges and seafloor spreading; (5) Magnetic stripes on ocean floor showing reversals; (6) Earthquake and volcano distribution; (7) GPS measurements of plate motion. Driving force: convection currents in the mantle from heat (radioactive decay, primordial). Pangaea: supercontinent ~250 million years ago, broke up into current continents. Earthquakes: caused by stress release along faults; measured by Richter or moment magnitude scale. Volcanoes: form where magma reaches surface.

Day and night are caused by Earth's rotation on its axis, which takes about 24 hours. As Earth spins, the side facing the Sun experiences day and the side facing away experiences night. Earth's orbit around the Sun (about 365 days) causes the year and, combined with the tilt of the axis, the seasons — not the daily day/night cycle. The Moon's gravity mainly drives the tides. Distinguishing rotation (daily spin → day/night) from revolution/orbit (yearly trip → year and seasons) is essential Earth-science knowledge.

Earth's crust is the thin, solid outermost layer where we live; it includes both continents and the ocean floor. Beneath it lies the mantle, a thick layer of hot, semi-solid rock that slowly flows, and below that the core (a liquid outer core and a solid inner core, composed largely of iron and nickel). The atmosphere is the layer of gases surrounding the planet, not a solid layer of the Earth itself. Knowing the order — crust, mantle, outer core, inner core — and their basic characteristics is standard Earth-science content.

Jupiter is the largest planet in our solar system — a gas giant whose mass is greater than all the other planets combined. Saturn is the second largest and is famous for its prominent rings. Earth and Mars are far smaller, rocky (terrestrial) planets. Basic astronomy facts like the order and relative sizes of the planets are part of Earth and space science. Jupiter's enormous size and its many moons make it a frequently referenced example; it is the giant of the solar system.