17-1: The Fossil Record Biology 2

Studying history of life is fascinating and challenging Scientists can study ancient rocks, sap from trees, bogs and pits, and polar glaciers FOSSILS: traces and preserved remains of ancient life Introduction

Paleontologists are scientists who collect and study fossils – They study structure of organisms, where they lived, what they ate (what ate them), environment where they lived FOSSIL RECORD: information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived Fossils and Ancient Life

Fossil occur in particular order Fossil records show where life on Earth has changed over time 99% of all species that have ever lived on Earth has become extinct – EXTINCT: term used to refer to a species that has died out Fossils and Ancient Life

For a fossil to form, organisms (or parts of organisms) must be preserved Formation of a fossil depends on a precise combination of conditions For every organism that dies and leaves a fossil, many more die without leaving a trace How Fossils Form

Fossils form in sedimentary rock – Sedimentary rock forms when rocks break down into small pieces – Pieces are carried away, and eventually settle to bottom Dead organisms may also sink to bottom and be covered – Weight of layers eventually push down and turns into rock How Fossils Form

Paleontologists determine age of fossils using 2 techniques : Relative Dating and Radioactive Dating RELATIVE DATING: method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock – INDEX FOSSILS: distinctive fossil used to compare the relative ages of fossils Relative Dating allows paleontologists to estimate fossil age compared with other fossils Interpreting Fossil Evidence

RADIOACTIVE DATING: technique in which scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains – Calculate how much of the elements in the fossils have decayed (broken down) to determine age Radioactive Dating allows scientists to calculate age of sample based on how much isotope remains Interpreting Fossil Evidence

GEOLOGICAL TIME SCALE: scale used by paleontologists to represent evolutionary time – It was first developed to study rock layers and index fossils Geological Time Scale put Earth’s rock layers in order according to relative age As they studied fossil layers, found “areas” where major changes occur in plants and animals – These “areas” mark where time periods begin and end Geological Time Scale

Geologists divide time between Precambrian and present into 3 eras: Paleozoic, Mesozoic, and Cenozoic – ERAS: one of several subdivisions of the time between the Precambrian and the present Paleozoic began about 544 million year ago and last about 300 million years Mesozoic began about 245 million years ago and last 180 million years Cenozoic began about 65 million years ago and continues to present Geological Time Scale

Eras are divided into periods – PERIODS: unit of time into which eras are subdivided Range in length from tens of millions to less than 2 million years Geological Time Scale

Eras are divided into periods – PERIODS: unit of time into which eras are subdivided Range in length from tens of millions to less than 2 million years Geological Time Scale