unit one

5. Lighter elements join together to form heavier elements
6. the universe formed in an instant, billions of years ago, in an enormous explosion
10. Exact number of years since the rock formed
11. large divisions of time
12. As a star begins to run out of fuel, the core shrinks,and the outer part expands
13. This is how we can tell if an object is moving toward or away from us
14. The amount of time it takes for half of the radioactive atoms to decay
15. Very large span of time
16. sheets of ice called glaciers cover large parts of Earth’s surface
17. smaller divisions of time

1. several different points in Earth’s history, all of the continents have been located close to each other
2. small changes that occur slowly
3. Manylakes were formed due to glaciation
4. hypothesized that Earth’scontinents were not always in their current locations
7. As the universe began to cool, and protons and neutrons were formed
8. A rock’s age compared to the ages of other rocks around it
9. Large numbers of species disappearing in a short period of time