GED Science 3 — Questions and Answers

Question 1: What is the primary cause of ocean tides on Earth?

Earth's rotation on its axis
The gravitational pull of the Moon (and Sun) (Correct answer)
Wind patterns across ocean surfaces
Differences in water temperature across the ocean

Correct answer: The gravitational pull of the Moon (and Sun)

Tides are primarily caused by the gravitational pull of the Moon on Earth's oceans. The Sun also contributes but to a lesser degree. The Moon's gravity creates bulges of water on the sides of Earth facing toward and away from the Moon.

Tides are the periodic rise and fall of sea levels caused by gravitational forces from the Moon and, to a lesser extent, the Sun. How lunar tides work: • The Moon's gravity pulls most strongly on the side of Earth nearest to it, creating a tidal bulge there • A second bulge forms on the FAR side of Earth due to inertia (centrifugal effect) • As Earth rotates, locations move through these bulges, causing two high tides and two low tides per day Spring tides vs. Neap tides: • Spring tides: Sun, Moon, and Earth align (new or full moon) → gravitational forces combine → highest tides • Neap tides: Sun and Moon are at right angles to Earth (quarter moons) → forces partially cancel → smaller tidal range The Moon has about 2.2× more tidal influence than the Sun despite the Sun being much more massive, because tidal force depends more on proximity than mass.

Question 2: How do scientists use the half-life of radioactive isotopes to determine the age of rocks and fossils?

By measuring the temperature of the rock sample
By counting the number of fossils in each rock layer
By comparing the ratio of parent to daughter isotopes in a sample (Correct answer)
By observing the color and texture of the rock

Correct answer: By comparing the ratio of parent to daughter isotopes in a sample

Radioactive isotopes decay at a known constant rate (half-life). By measuring the ratio of remaining parent isotope to daughter product, scientists calculate how long the decay has been occurring.

Radiometric dating uses the known, constant decay rates of radioactive isotopes to determine the age of materials. Key concept: Half-life — the time for exactly half of a radioactive parent isotope to decay into the daughter product. Each isotope has a unique, unchanging half-life. Examples of radiometric dating methods: • Carbon-14 (¹⁴C): half-life ~5,730 years → used for organic materials up to ~50,000 years old (archaeology, recent fossils) • Potassium-40 (⁴⁰K): half-life ~1.25 billion years → used for very old rocks and fossils • Uranium-238 (²³⁸U): half-life ~4.5 billion years → used for Earth's oldest rocks Dating process: 1. Measure current ratio of parent to daughter isotope in a sample 2. Apply decay formula to calculate elapsed time For example: if half the ¹⁴C has decayed, the sample is ~5,730 years old; if only 1/4 remains, it's ~11,460 years old (two half-lives).

Question 3: What process drives the movement of tectonic plates?

The gravitational pull of the Moon
Convection currents in Earth's mantle (Correct answer)
Earth's magnetic field
Solar radiation heating the surface

Correct answer: Convection currents in Earth's mantle

Convection currents in the semi-molten mantle drive plate movement. Hot material rises, spreads, cools, and sinks, creating a conveyor-belt-like motion that moves the plates above.

Tectonic plates move because of convection currents in Earth's mantle: Convection process: 1. Heat from Earth's core warms the lower mantle 2. Hot, less dense mantle rock rises slowly 3. Near the surface, rock cools and becomes denser 4. Dense rock sinks back down 5. This circular motion drags the overlying tectonic plates Additional driving forces: • Ridge push: at mid-ocean ridges, new crust forms and pushes older crust outward • Slab pull: at subduction zones, dense oceanic crust sinks, pulling the plate behind it Plate movement rates: typically 2–15 cm per year (about as fast as fingernails grow) Earth's structure: • Inner core (solid iron-nickel): ~5,400°C • Outer core (liquid iron-nickel): generates magnetic field • Mantle (semi-solid rock): site of convection currents • Crust (thin solid layer): where we live; divided into tectonic plates

Question 4: The Hertzsprung-Russell (H-R) diagram classifies stars based on which two properties?

Mass and diameter
Temperature and luminosity (brightness) (Correct answer)
Age and distance from Earth
Color and rotation speed

Correct answer: Temperature and luminosity (brightness)

The H-R diagram plots stars by surface temperature (x-axis, hot on left) versus luminosity/brightness (y-axis). This reveals patterns including the main sequence, giants, supergiants, and white dwarfs.

The Hertzsprung-Russell (H-R) diagram, developed independently by Ejnar Hertzsprung and Henry Norris Russell in the early 1900s, is one of astronomy's most important tools. Axes: • X-axis: Surface temperature (hot/blue stars on LEFT, cool/red stars on RIGHT — counterintuitive!) • Y-axis: Luminosity or absolute magnitude (bright at top, dim at bottom) Major groups on the H-R diagram: • Main Sequence (diagonal band from top-left to bottom-right): stars fusing hydrogen in their cores, including our Sun. Most stars spend most of their lives here. • Red Giants/Supergiants (upper right): large, cool, bright stars (e.g., Betelgeuse) • White Dwarfs (lower left): small, hot, dim remnants of dead stars Stellar evolution: Stars move along the H-R diagram as they age. A star like our Sun will eventually leave the main sequence and become a red giant, then a white dwarf.

Question 5: What happens at a convergent plate boundary where oceanic crust meets continental crust?

New ocean floor is created as magma rises
The continental crust subducts beneath the oceanic crust
The oceanic crust subducts beneath the continental crust, forming mountains and volcanoes (Correct answer)
Both plates move sideways past each other

Correct answer: The oceanic crust subducts beneath the continental crust, forming mountains and volcanoes

Oceanic crust is denser than continental crust, so it subducts (sinks) beneath the continental plate. This creates deep ocean trenches, volcanic mountain ranges, and earthquakes.

At convergent plate boundaries, plates move toward each other. The outcome depends on the types of crust involved: Oceanic-Continental convergence: • Oceanic crust (density ~3.0 g/cm³) is denser than continental crust (density ~2.7 g/cm³) • Oceanic plate SUBDUCTS (sinks) beneath the continental plate • Creates deep ocean trenches (e.g., Peru-Chile Trench) • As oceanic crust sinks and melts, magma rises → continental volcanic mountains (e.g., Andes Mountains, Cascade Range) • Intense earthquakes occur along the subduction zone Oceanic-Oceanic convergence: denser plate subducts → volcanic island arcs (e.g., Japan, Aleutian Islands) Continental-Continental convergence: neither plate subducts (both too light) → folded mountain ranges (e.g., Himalayas, Alps, Appalachians) Divergent boundaries: plates move apart → new oceanic crust forms (mid-ocean ridges) Transform boundaries: plates slide past each other → earthquakes (e.g., San Andreas Fault)

Question 6: In which layer of Earth does the material behave like a slow-moving fluid, allowing tectonic plates to move?

Outer core
Inner core
Crust
Mantle (Correct answer)

Correct answer: Mantle

The mantle, particularly the asthenosphere layer, is composed of semi-molten rock that behaves plastically (like a very thick fluid) over long timescales, enabling tectonic plate movement.

Earth's interior structure from surface to center: 1. Crust: thin outer layer (5–70 km thick); rigid; where we live; divided into oceanic and continental crust 2. Mantle: largest layer (~2,900 km thick); makes up ~84% of Earth's volume; composed of silicate rock • Lithosphere (upper rigid mantle + crust): the tectonic plates • Asthenosphere: semi-molten, plastic rock (~100–350 km depth); moves like a very slow fluid; tectonic plates 'float' on this layer • Lower mantle: solid despite high temperatures (pressure too high for melting) 3. Outer core: liquid iron and nickel (~2,900–5,150 km); flowing iron creates Earth's magnetic field 4. Inner core: solid iron and nickel (~5,150–6,370 km); solid despite extreme heat (~5,400°C) because of enormous pressure The asthenosphere's plastic behavior is what allows tectonic plates to move. The temperature is high enough to partially melt rock, reducing viscosity and enabling slow convection currents.

GED Science 3

What is the primary cause of ocean tides on Earth?