Geologic Time Vocab Crossword

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

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