Across
- 2. an igneous rock layer formed when lava flows on surface layers of rock and hardens
- 4. a gap in the geologic record; usually caused by erosion, flood, earthquake or other natural causes
- 6. an igneous rock layer when magma hardens below the Earth's surface
- 7. time in history when organisms with spines appeared (vertebrates: fish, insects, and small reptiles) era that began about 544 million years ago and lasted for almost 300 million years
- 8. says that the oldest rocks lie on the bottom and the youngest rocks are on top of any undisturbed sequence of sedimentary rocks.
- 10. a fossil found in a narrow time range but widely distributed around the earth; used to date rock layers
- 12. the process by which the age of a rock is determined by measuring the amount of radioactive isotopes present in the rock or rock sample
- 15. covers about 88% of the Earth's history, bacteria came first and soft multi-cellular organisms arrived toward the end
- 16. a more specific age for a rock, mineral, or other object; done with carbon-dating or radioactive dating; not always the EXACT age
Down
- 1. process in which sediment is laid down in new locations
- 3. a record of all biological and geological evolution (changes over time)
- 5. era that began about 66 million years ago and is the time in Earth's we live in now; a.k.a "Age of Mammals"
- 9. an index fossil that looks like a cockroach
- 11. All plants and animals contain some amount of carbon-14. As long as the organism is alive, the amount of carbon-14 stays the same. After an organism dies, then no more carbon is added and the carbon-14 in the organism's body starts radioactive decay.
- 13. era that began 245 million years ago, a.k.a. "Age of the dinosaurs"
- 14. the age of an object compared to the ages of rock layers or fossils near it; used w/ Law of Superposition; an estimation of age