Chapter 12: The History of Life

Section One: The Fossil Record Fossils Used to date time an organism lived Relative dating: estimates the time during which an organism lived by comparing the placement of fossils of the organism with the placement of fossils in other layers of rock Usually use carbon dating

Section Two: The Geologic Time Scale Index fossils Fossils of organisms that existed only during specific spans of time over large geographic areas The shorter the life span of the organism, the closer we can date the time it was living

Section Two: The Geologic Time Scale A representation of the history of the Earth Divided into Eras: last tens to hundreds of millions of years and consist of 2 or more periods Periods: lasting tens of millions of years Epochs: the smallest units that last several million years

Section Four: Early Single-Celled Organisms Endosymbiotic Theory Endosymbiosis A relationship in which one organism lives in the body of another, and both benefit from the relationship Suggests that chloroplasts and mitochondria were once simple prokaryotic cells that were engulfed by larger prokaryotes