Science Earth and Space Science Flashcards

Geologists studying the ocean floor notice that oceanic crust sits at progressively greater depths the farther it is from a mid-ocean ridge. What is the PRIMARY reason for this pattern?

Answer: The crust cools and contracts as it moves away from the ridge, becoming denser and sinking

Oceanic crust is formed hot and buoyant at mid-ocean ridges. As it spreads away and ages, it loses heat to the ocean. Cooler rock is denser, so it sinks lower into the mantle in a process called isostatic adjustment. This is why the oldest oceanic crust, just before it subducts, lies in the deepest ocean trenches.

Scientists drill ice cores in Antarctica and find trapped air bubbles that allow them to reconstruct atmospheric CO₂ concentrations going back 800,000 years. They observe that CO₂ rises and falls in roughly 100,000-year cycles that closely match cycles of glaciation. Which astronomical cycle most strongly corresponds to this ~100,000-year periodicity?

Answer: Changes in the shape of Earth's orbit (eccentricity), which cycle every ~100,000 years

Milankovitch cycles describe three periodic changes in Earth's orbit and orientation. Eccentricity — how elliptical vs. circular Earth's orbit is — operates on a ~100,000-year cycle and most closely matches the major glacial-interglacial pattern seen in ice cores. When the orbit is more elliptical, seasonal differences in solar energy receipt are amplified. Obliquity (~41,000 yr) and precession (~26,000 yr) are also real but operate on shorter timescales.

After the last ice age ended roughly 12,000 years ago, enormous ice sheets melted from Scandinavia. Today, GPS measurements show parts of Scandinavia are still rising at up to 8 mm per year, even though all the ice is gone. What process best explains this ongoing uplift?

Answer: The mantle is slowly flowing back beneath the crust as it rebounds from the removed glacial weight

This is called isostatic rebound (or post-glacial rebound). The mantle, though solid on short timescales, behaves plastically over thousands of years. The massive weight of ice sheets pushed the crust down into the mantle. When the ice melted, the load was removed, and the mantle material that had been displaced is slowly flowing back, allowing the crust to rise. The process is still ongoing because mantle flow is very slow.

A geologist finds a zone of marble within a limestone formation, but only within about 200 meters of a large granite body that intruded into the region. Farther from the granite, the limestone is unchanged. What type of metamorphism produced this marble, and what was the primary driving factor?

Answer: Contact metamorphism driven by heat radiating from the nearby igneous intrusion

The restricted zone of metamorphism immediately surrounding the granite intrusion is a classic aureole produced by contact metamorphism. The molten granite brought intense heat, which recrystallized the adjacent limestone into marble without requiring great pressure or tectonic forces. The fact that the effect disappears with distance — and correlates spatially with the intrusion — points directly to heat, not pressure or fluids, as the primary agent.

On a Hertzsprung-Russell (H-R) diagram, a star is plotted in the upper-right region — meaning it has very HIGH luminosity but a LOWER surface temperature (appearing orange-red) compared to the Sun. How should this star be classified, and what does its position tell us about its size?

Answer: A red giant or supergiant — an evolved star with an enormously expanded outer shell

High luminosity combined with relatively low surface temperature can only be explained by enormous surface area — the star must be physically huge. Stars reach this stage late in their lives: after exhausting core hydrogen, they expand dramatically into red giants or supergiants. White dwarfs are hot but tiny (low luminosity). Neutron stars are not plotted on standard H-R diagrams as visible stars. Main-sequence stars follow a diagonal band from lower-right to upper-left.

The Moon always presents the same hemisphere toward Earth — a phenomenon called tidal locking. Which mechanism is primarily responsible for causing the Moon's rotation to slow and synchronize with its orbital period over billions of years?

Answer: Earth's gravity creating a tidal bulge on the Moon; friction from the non-aligned bulge dissipated rotational energy until the spin matched the orbit

Earth's gravitational field is slightly stronger on the Moon's near side than its far side, creating a tidal bulge elongated toward Earth. Early in the Moon's history, when it rotated faster than it orbited, this bulge was pulled slightly ahead of the Earth-Moon line. The gravitational torque on that misaligned bulge continuously slowed the Moon's rotation — converting rotational kinetic energy into heat through internal friction — until rotation and orbit finally matched, eliminating the torque. This same process is actively slowing Earth's own rotation (lengthening our day) as the Moon raises tides on Earth.