Igneous & Metamorphic
What type of rock forms when magma cools and hardens?
Igneous rock.
What is the name for rock formed from compressed and cemented sediments?
Sedimentary rock.
What is a fossil?
Preserved remains or traces of past life.
State the Law of Superposition for undisturbed rock layers.
In undisturbed layers, the oldest rock is at the bottom and the youngest is at the top.
What is weathering?
Breaking down rock into smaller pieces (weathering).
Name the process that changes a rock by heat and pressure without melting.
Metamorphism (or metamorphic process).
List the correct sequence of steps that form sedimentary rock starting from weathering.
Weathering → erosion → deposition → compaction → cementation.
What is the difference between a mold fossil and a cast fossil?
Mold: an impression left after an organism decays; Cast: a 3D fossil formed when minerals fill a mold.
What is relative age?
Relative age is the age compared to other layers (older or younger), not a number of years.
What is a rock strata?
Rock strata are layers of rock.
Explain briefly how an igneous rock can become a metamorphic rock (two steps).
The igneous rock is buried and then exposed to high heat and pressure, causing mineral changes and forming metamorphic rock.
Define erosion in one sentence.
Erosion is the movement of sediments by wind, water, ice, or gravity.
Give two examples of trace fossils.
Footprints, burrows (also trails, coprolites).
What does absolute age tell you that relative age does not?
Absolute age gives the actual age in years (e.g., millions of years) using methods like radiometric dating.
Explain in one sentence what radiometric dating measures
Radiometric dating measures the decay of radioactive isotopes to determine absolute age.
Identify whether the following is igneous, metamorphic, or sedimentary: a rock with ribbon-like minerals formed under high pressure.
Metamorphic (ribbon-like minerals = foliated metamorphic rock).
Explain the difference between compaction and cementation.
Compaction presses sediments together physically; cementation is when minerals precipitate and act like glue to bind sediments.
What is a body fossil? Give one example.
Body fossil = actual remains such as bones, teeth, or shells. Example: a dinosaur bone.
Define half-life in one sentence.
Half-life is the time needed for half of a radioactive element to decay.
Give the complete rock-cycle example:
igneous → ______ → sedimentary → ______.
igneous → sediment → sedimentary → metamorphic.
Describe how cooling rate affects crystal size in igneous rocks (slow vs. fast).
Slow cooling (deep underground) produces larger crystals; fast cooling (lava at surface) produces small crystals or glassy texture.
Give an example of a specific environment where sediment deposition commonly occurs and why it helps form sedimentary rock.
River delta — water slows and drops sediments, allowing layers to build up and later compact/cement into rock.
Explain why rapid burial and lack of oxygen help fossil formation.
Rapid burial protects remains from scavengers and decay; lack of oxygen slows decomposition and prevents bacteria that break down organic material.
Describe how index fossils are useful for matching rock layers across long distances (include two required qualities of index fossils).
Index fossils are widespread, lived for a short time, and are easily recognizable; they let geologists correlate layers by showing which layers are the same age across distances.
Describe two reasons fossils are rare (provide two different causes).
Two reasons: Most organisms decay before they are buried; heat and pressure during deep burial can destroy fossil evidence.