1. Index Fossils and Geologic Time “The Past is the Key to the Present”

2. Determining Relative Age  Rock layers (strata) detail sequences of Earth’s events  the oldest rock layers are on the bottom and youngest are on top  Relative Age (Approximate)  Fossils  Rock layers (strata) detail sequences of Earth’s events  the oldest rock layers are on the bottom and youngest are on top  Relative Age (Approximate)  Fossils

3. Determining Absolute Age  Absolute Age = Exact Age  Radioactive Decay  Half-Life  Carbon Dating  Fossils  Absolute Age = Exact Age  Radioactive Decay  Half-Life  Carbon Dating  Fossils

4. The Fossil Record  Remains or traces of animals or plants from a previous geologic time  Quick burial; Sedimentary Rock  Used for absolute and relative ages  Fossil succession (fossils succeed one another in a definite order)  Remains or traces of animals or plants from a previous geologic time  Quick burial; Sedimentary Rock  Used for absolute and relative ages  Fossil succession (fossils succeed one another in a definite order)  Kinds of Fossils  Hard Parts  Trace (footprint)  Imprints, molds and casts  Coprolites (dino doo-doo)  Gastroliths (Digestive stones)

5. Index Fossils  Fossils found exclusively in rock layers of a particular geologic age  Present over a wide area  Easily distinguished  Relatively short geologic time span  Large numbers within rock layers

6. More on Index Fossils  Used to establish the relative ages of the rock layers in which the fossils are found (trilobite)  Used to date rock layers found in widely separated areas  Used to locate oil and natural gas deposits  Used to establish the relative ages of the rock layers in which the fossils are found (trilobite)  Used to date rock layers found in widely separated areas  Used to locate oil and natural gas deposits

7. Geologic Time  Fossil record (worldwide) used to construct a “geologic column” which shows the ordered arrangement of rock layers based upon ages  Distinguished primarily by kinds of fossils they contain  Fossils in the lower, older layers are very different than those within the younger layers  Fossil record (worldwide) used to construct a “geologic column” which shows the ordered arrangement of rock layers based upon ages  Distinguished primarily by kinds of fossils they contain  Fossils in the lower, older layers are very different than those within the younger layers

8. Divisions of Geologic Time  Earth’s geologic history is punctuated by major changes in the earth’s surface or climate and by the extinction of various species  Geologists use these events as the basis for dividing the geologic time scale (Eons) into smaller units  Eras  Periods  Epochs  Earth’s geologic history is punctuated by major changes in the earth’s surface or climate and by the extinction of various species  Geologists use these events as the basis for dividing the geologic time scale (Eons) into smaller units  Eras  Periods  Epochs

10. Precambrian Time  4.6 bya to 570 mya  88% of Earth’s history  Atmosphere forms  Fossils rare  Soft-bodied  Deformed rock  Bacterial reefs  Worms, jellyfish and one-celled organisms in late precambrian

11. Paleozoic Era  570 mya to 245 mya  Dramatic increase in plant and animal species  Rich marine and land fossil record

12. More on the Paleozoic Era  First vertebrates (fishes) appear  First land plants and animals appear  First amphibians appear  First reptiles appear  Pangaea comes together  Mass extinctions mark the end of this era  Marine invertebrates (trilobites, eurypterids) due to retreat of the seas  First vertebrates (fishes) appear  First land plants and animals appear  First amphibians appear  First reptiles appear  Pangaea comes together  Mass extinctions mark the end of this era  Marine invertebrates (trilobites, eurypterids) due to retreat of the seas

13. Mesozoic Era  245 mya to 65 mya  Surface of the earth changed dramatically (break-up of Pangaea)  Conditions favored the survival of the reptiles  245 mya to 65 mya  Surface of the earth changed dramatically (break-up of Pangaea)  Conditions favored the survival of the reptiles

14. More on the Mesozoic Era  Dinosaurs first appear  First mammals appear  Flying reptiles and first birds appear  First flowering plants appear  Mass extinctions (dinosaurs, marine animals) mark the end of this era  Cretaceous-Tertiary Boundary (K-T)  Meteorite-Impact hypothesis  Dinosaurs first appear  First mammals appear  Flying reptiles and first birds appear  First flowering plants appear  Mass extinctions (dinosaurs, marine animals) mark the end of this era  Cretaceous-Tertiary Boundary (K-T)  Meteorite-Impact hypothesis

15. Cenozoic Era  65 mya to present  Time of increased tectonic activity  Dramatic changes in climate (ice ages)

16. More on the Cenozoic Era  “Age of Mammals”  Divided into two periods:  Tertiary: time before the last major ice age  Whales, Horses, deer, grazing herds, wolves, raccoons  Quaternary: Last ice age (Pleistocene) to present  Wooly mammoths, rhinos, humans  “Age of Mammals”  Divided into two periods:  Tertiary: time before the last major ice age  Whales, Horses, deer, grazing herds, wolves, raccoons  Quaternary: Last ice age (Pleistocene) to present  Wooly mammoths, rhinos, humans