8th Grade Unit 4 Vocab

2. a method used to determine the specific age of an object in actual years
4. any material (like a fragment of another rock, a mineral crystal, a or a trapped gas bubble) that is found inside a larger rock or mineral
5. by observing current events like erosion and sedimentation, we can understand how past geological formations like mountains and valleys were created over long periods of time.
7. a gap in the sequence of rock layers, representing a period of time where no new rocks were deposited, or where existing rocks were eroded away
8. the time it takes for half of a group of unstable atoms to decay into a different element
11. the process where molten rock (magma) forces its way into or between existing rock layers beneath the Earth's surface and then cools and solidifies
13. a system for organizing Earth's 4.6-billion-year history into a "calendar" of divisions like eons, eras, periods, and epochs

1. a geology principle that states that in an undisturbed sequence of rock layers, the oldest layers are at the bottom and the youngest are at the top
3. a preserved remnant or trace of ancient plant or animal life, like a bone, tooth, footprint, or impression
6. a fossil of an organism that lived for a short, specific period of time and was widespread geographically
9. a scientific method that determines the age of rocks and other materials by measuring the decay of radioactive isotopes inside them
10. a principle that states any geologic feature that cuts across existing rocks is younger than the rock it cuts
12. a science method that determines the chronological order of events without assigning a specific numerical age