2. What is the Earth’s time scale? The Geological time scale is a record of the life forms and geological events in Earth’s history. Scientists developed the time scale by studying rock layers and fossils world wide. Radioactive dating helped determine the absolute divisions in the time scale.

3. Relative Dating Relative dating: looks at where the fossil is located to determine its age relative to other fossils. Does not give an exact age of the fossil. This only works if the area has been undisturbed.

4. Absolute Dating Uses radioactive elements near the fossils to determine the actual age of the fossils. By determining the age of the radioactive element, scientists can calculate the age of the fossil buried nearby. The absolute age of fossils is estimated by dating associated igneous rock and lava flows.

5. Fossil: The actual remains or evidence of a living thing. of a living thing.

6. Types of Fossils Molds and Casts: Types of Fossils Molds and Casts: Mold: Mold: mold fossil is formed when an object is placed into soft mud and is removed by decomposition-leaves a negative impression. Cast: Type of fossil that forms when mineral crystals fill a mold or sediments wash into a mold and harden into rock.

7. Trace fossils: Trace fossils: Non-body remains indicating the activities or behavior of an organism. Examples of trace fossils: tracks, trails, footprints, burrows, and fossil feces.

8. Fossil Record The dating of all fossils is included in the Geological Time Scale. This scale divides the time that the earth has existed into 4 eras. Eras are then divided into periods based on common events in that time period.

9. Divisions of Geologic Time Eras are subdivided into periods...periods are subdivided into epochs. Era Period Epoch

10. Divisions of Geologic Time Geological time begins with Precambrian Time. Precambrian time covers approximately 88% of Earth’s history.

11. FOUR Eras… oldest to most recent PRE-CAMBRIAN – 88% of earth’s history Paleozoic (ancient life) –544 million years ago…lasted 300 million yrs Mesozoic (middle life) –245 million years ago…lasted 180 million yrs Cenozoic (recent life) –65 million years ago…continues through present day

12. Today… Today we are in the Holocene Epoch of the Quaternary Period of the Cenozoic Era.