A Trip Through Geologic Time

2. A vertebrate whose body temperature is regulated by its internal heat, and has skin covered with hair or fur and glands that produce milk to feed its young
3. An igneous rock layer formed when lava flows onto Earth's surface and hardens
6. The time it takes for half of the atoms of radioactive elements to decay
8. A break in Earth's crust along which rocks move
10. An igneous rock layer formed when magma hardens beneath Earth's surface
12. A record of the geologic events and life forms in Earth's history
13. A vertebrate whose body temperature is determined by the temperature of its environment, that has lungs and has scaly skin, and lays eggs on land
14. A type of fossil that provides evidence of activities of an ancient organism
16. A gap in the geologic record that shows were rock layers have been lost due to erosion
17. A fossil in which minerals replace all or part of an organism
18. An animal with a backbone
19. A type of fossil consisting of an extremely thin coating of carbon on rock
22. The age of rock given as the number of years since the rock formed
23. A type of fossil that is a hollow area in sediment in the shape of an organism or part of an organism
24. A scientist who studies fossils to learn about organisms that lived long ago
26. The age of rock compared to the ages of other rocks
28. Change over time; the process by which modern organisms have descended from ancient organisms

1. A vertebrate whose body temperature is determined by the temperature of its environment, and lives its early life in water and its adult life on land
3. Term used to refer to a group that have died out and no longer have any living members
4. Fossils of widely distributed organisms that lived through a geologically short period
5. The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it
7. One of the three long units of geologic time between the Precambrian and the present
9. The process in which the nuclei of radioactive elements break down, releasing fast moving particles and energy
11. When many types of living things become extinct at the same time
15. The preserved remains or traces of an organism that lived in the past
20. A fossil that is a solid copy of an organism's shape formed when minerals seep into the mold
21. An animal without a backbone
25. One of the three units of geologic time in which geologists divide eras
27. A loose connection of ice and dust that orbits the sun, typically a very narrow orbit