Understanding the Rock Cycle

• The rock cycle illustrates how rocks on Earth change and form over time.
• Rocks pushed deep below the surface can melt into magma, which becomes lava when it reaches the surface through volcanic activity.

Igneous Rocks

• Igneous rocks are created as magma or lava cools and solidifies

Sedimentary Rocks

• Weathering breaks rocks into sediment, then erosion transports it, and deposition drops it in a new location.
• Sedimentary rocks form when sediment is compacted and cemented through lithification.

Metamorphic Rocks

• Metamorphic rocks are existing rocks altered by intense heat and pressure, and can be formed from igneous, sedimentary, or other metamorphic rocks.
• Sedimentary rocks typically occur in horizontal layers called strata.
• The law of superposition states that in undisturbed strata, younger layers are on top of older ones.
• Faults (cracks in the Earth’s crust) and intrusions (igneous rock within the crust) can cut through strata.
• The law of crosscutting relationships dictates the feature that cuts through another is younger.
• Index fossils, associated with a specific time, can indicate that strata formed around the same time.
• Geologists use strata to determine the relative order of major events in Earth’s history, represented by the geologic time scale.

Tectonic Plates

• The Earth’s lithosphere is divided into tectonic plates that move slowly over the asthenosphere.
• Tectonic plates move at an average of a few centimeters per year.
• Plate boundaries are the places where two plates meet.
• Divergent boundaries: plates move apart, form rift valleys and mid-ocean ridges.
• Convergent boundaries: plates move together, form mountains and trenches.
• Transform boundaries: plates move past each other, cause earthquakes.
• Complementary coastlines suggest that continents were once joined, providing evidence for plate motion.

Oceanic and Continental Plates

• Oceanic plates form the ocean floor, whereas continental plates form the continents.
• Oceanic crust is denser than continental crust.
• Trenches form when a denser oceanic plate is subducted under a less dense plate at a convergent boundary.
• Mid-ocean ridges form when two oceanic plates move apart at a divergent boundary.
• New oceanic crust is created at mid-ocean ridges, ages as it moves away, eventually reaching a trench and is destroyed.

Water and Earth's Surface

• Water movement shapes the Earth’s surface through weathering, erosion, and deposition.
• Weathering breaks down rocks and soil into sediment
• Mechanical weathering: Sediment created through physical means.
• Chemical weathering: Sediment creation through chemical reactions.
• Erosion: Water transports sediment.
• Water has greater erosional power with faster flow and more volume.
• Deposition/Sedimentation: Water drops sediment in a new location.