1. Semester Exam Review
Geologic Timeline

2. Index Fossils
Ammonite fossils are found in great quantities and are used as an index fossil.
Index fossils are commonly found fossils that are limited in a particular time span. They help in dating other fossils.
Ammonites only existed during the Mesozoic Era, but went extinct at the end of the Cretaceous period.

3. Cambrian Period 540 to 500 mya “The Age of Trilobites”
Trilobites are the index fossils used for the Cambrian Period.

4. Decomposers
Many types of decomposers live in the top layers of soil. These decomposers can break down dead organisms before they can harden into fossils.
Decomposers: bugs, worms, bacteria, vultures, etc.

5. Devonian Period 408 to 360 mya “The Age of Fish”
Amphibians, sharks, & bony fish

6. Mississippian Period 360 to 325 mya First winged insects
Known for giant insects.
The first known dragonfly fossil had a wingspan of about 29 inches.

7. Tyrannosaurus Rex came into existence during the Cretaceous Period.

8. Tertiary Period 65-1.8 mya First hominids (australopithecines)
Modern forms of whales
Megalodon swam the seas
australopithecines

9. Pleistocene 1.8 million to ~10,000 years ago
Mammoths, longhorned bison, saber-toothed cats, giant ground sloths
Giant teratorn birds with 25-foot wingspans stalked prey
Around the end of the Pleistocene, all these creatures went extinct.
Giant teratorn bird

10. Holocene 11,000 years ago to today Modern Human civilization
The Last Ice Age ended 10,000 years ago.
Scientists say there will be another ice age.