Geoscience

Extrusive vs. intrusive?

• Extrusive: Forms from lava at the surface; cools fast; small/no crystals.

• Intrusive: Forms from magma underground; cools slowly; large crystals.

Coarse vs. fine-grained?

• Coarse: Large crystals (slow cooling).

• Fine: Small crystals (fast cooling).

Mafic vs. felsic?

• Mafic: Low silica, dark color, high density.

• Felsic: High silica, light color, low density.

Q: What controls the texture of an igneous rock?

Cooling rate.

Vesicular texture?

Full of gas bubble holes.

Glassy texture?

Very rapid cooling; no crystals.

Fine-grained texture?

Rapid cooling; tiny crystals.

Porphyritic texture?

large and small crystals

How does cooling rate affect crystal size?

Slow cooling → large crystals; fast cooling → small crystals.

How does porphyritic texture form?

Two-stage cooling: slow underground, then fast at the surface.

Effect of silica content on magma?

High silica = thicker, lighter color, less dense.

What is an ultramafic rock & where is it found?

Very low silica, very dark, very dense; found in Earth’s mantle.

Where are most sedimentary rocks found?

At or near Earth’s surface.

What are the 3 main sedimentary groups?

• Clastic: From broken rock fragments.

• Organic/Biochemical: From once-living material (shells, plant remains).

• Chemical: From minerals precipitating out of solution.

Q: Why are sedimentary rocks layered?

A: They form from repeated deposition of sediments.

Q: Why/how are sediments sorted?

A: By size; water/wind sort them based on energy levels.

Q: Why are quartz and feldspar common in sand & sed rocks?

A: They are very resistant to weathering.

Q: Two ways sediments become sedimentary rock?

A: Compaction and cementation.

Q: How are sediments usually transported?

A: Mostly by running water.

Q: Why are some sediments angular vs. rounded?

A: Longer travel = more rounding.

Q: Weathering vs. erosion vs. deposition?

• Weathering: Breaking down rocks.

• Erosion: Moving sediments.

• Deposition: Dropping sediments to rest.

: What 3 processes create metamorphic rocks?

A: Heat, pressure, and chemical fluids.

Q: Regional vs. contact vs. hydrothermal metamorphism?

• Regional: Mountain-building; large areas; high pressure.

• Contact: Magma heats nearby rock.

• Hydrothermal: Hot fluids alter rock.

: Foliated vs. nonfoliated?

• Foliated: Minerals aligned in layers/bands.

• Nonfoliated: No visible banding; uniform texture.

3 changes metamorphism causes?

New minerals, new texture (foliation), increased density.

Q: What is the rock cycle?

A: The processes that transform rocks between igneous, sedimentary, and metamorphic through melting, cooling, weathering, erosion, deposition, heat/pressure, and uplift.

Q: Perpetual vs. renewable vs. non-renewable?

• Perpetual: Never runs out (sun, wind).

• Renewable: Replenishes but can run out short-term (trees, water).

• Non-renewable: Takes millions of years to form (oil, coal, gas).

Q: What is energy & past vs. present sources?

Energy = ability to do work.
Historically: wood, coal.
Today: oil, natural gas, renewables.

How is oil created?

A: Burial of marine organisms, heat + pressure over millions of years.

Q: Why is oil non-renewable?

A: Takes millions of years to form; we use it much faster than it forms.

Q: Oil–food–population connection?

A: Oil powers farming, transport, fertilizers → supports large populations.

Q: Issues with the U.S. importing ~50% of oil?

A: Economic risk, political dependence, rising costs.

Q: What is “Peak Oil”?

A: The point when oil production reaches its maximum, then declines.

Q: Examples of energy alternatives?

A: Solar, wind, hydro, nuclear, geothermal, biofuels.

Q: Pros & cons of alternatives?

• Pros: Clean, renewable, reduces emissions.

• Cons: Expensive, location-dependent, storage issues.

: What is fracking & why does it matter?

A: Injecting fluid to crack rock and release oil/gas; increases production but can cause environmental issues.

3 ways to transition from cheap to expensive oil?

A: Efficiency, alternative energy, new technology.

Q: Conventional vs. unconventional oil?

• Conventional: Flows easily; cheap.

• Unconventional: Harder to extract (shale, tar sands).