History of the Earth

3. _________ is the time it takes for half of a substance to decay.
5. During a mass _____ many types of living things become extinct at the same time
8. The __________ Period is the oldest period in the Earth's history
11. ____________ rocks are made from lava that has cooled down.
13. This kind of fossil dating only says if fossils are older or younger than the ones around them.
14. The Law of _____________ States that older rocks are on the bottom and newer rocks are on the top.

1. ___________ was a supercontinent that formed 320 million years ago
2. By looking at the ________ time scale, it can tell us the about the timeline of rocks and fossils recorded on the Earth.
4. A gap or interruption in a rock formation that shows where erosion occurred, where there may be a gap in the fossil record.
6. A large subdivision of geologic time that marks a major change in Earth's history.
7. A smaller division of time within an era
9. Scientists use _________ dating to determine how old, in number of years, a fossil is.
10. During _________ decay, atoms of one element break down into more stable elements and release radiation at the same time
12. A large landmass that holds most of the earth's land