1						2							3
					4																	5
															6
					7					8
	9																		10
					11
12
13						14								15
																			16			17
											18		19
	20										21						22
				23
			24
25
		26								27
28

Across 4. "old life" 6. type of trace fossil 9. priniciple that states that the geological processes that are acting on the Earth today are the same as those that acted upon the Earth in the past 11. principle that states that the younger rock layers lie above older rock layers in undisturbed sequences 13. process where organisms do not decay because the bacteria that feeds on the dead organism can't live without water 15. the time it takes for one half of a radioactive sample to decay 16. type of fossil where the animal's acitivity is preserved 18. an index fossil 23. ideal sequence of rock layers that contain all known fossils and rock formations 25. preserved feces 26. a cavity in ground where a plant or animal was buried 27. era where reptiles dominated 28. naturally preserved evidence of life

Down 1. missing part or gap in the geologic column 2. a process in which mineral fill in the pore spaces of an organism's tissue 3. occurs when an organism's tissue is completely replaced by minerals 5. dating technique that uses the principle of superposition to determine if an object or event is older or younger than another object or event 7. four major parts of the geologic time scale 8. most of the fossils of saber-toothed cats are found here 10. dating technique that establishes the age of an object 12. insects are often preserved in this 14. fossils of organisms that lived during a relatively short, well defined time period 17. object created when a mold is filled with sediments that become rock 19. atoms of the same element with different masses 20. unconfomity that exists between horizontal rock layers and rock layers that are tilted or folded 21. the process where an unstable isotope changes into a stable isotope 22. era where mammals dominated 24. trace fossil of shelters made by animals