Fossils & The Geologic Time Scale

Anticipation Guide• If you agree with the statement, put an √

beside it. If you disagree with the statement, put an X beside it.

• ____ 1. Fossils show how plants and animals have changed over time.

• _____2. It is rare for the soft parts of an organism to become a fossil.

____ 3. A footprint is an example of a trace fossil.

• ____ 4. A petrified fossil is an animal that was scared just before it died.

Fossils• Preserved remains or traces of an organism

that lived in the past.•Fossils are formed when organisms die and are buried in sediment. Eventually the sediment builds up and hardens to become sedimentary rock.•Sediments are pieces of solid material that have been deposited on Earth’s surface by wind, ice, gravity, or chemical precipitation. •Paleontologist-scientist who study the remains of organisms in the rock record.

Kinds of fossils• Petrified - when minerals replace the remains and

they become rock things like wood.• Mold - when the shell remains and the contents

dissolve (hollow) like in art class you use a mold to get the correct shape of a bowl.

• Cast - when the mold becomes filled with minerals that are not a part of the original organism.

• Index- a fossil found in a narrow time range but widely distributed around the earth;used to date rock layers.

• Trace fossil-a fossilized mark that is formed in soft sediment by the movement or actions of an animal.

PETRIFIED MOLD

CAST

• Sometimes whole animals become preserved intact, but this is very rare. If an organism is surrounded by ice or tar they might be discovered looking much the same as they did when they died.

AETOSAUR

FOUND IN THE NATIONAL PETRIFIED FOREST

Relative Dating Relative dating: looks at where the fossil is

located to determine its age relative to other fossils. This only works if the area has been undisturbed.

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.

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.

Anticipation Guide

Anticipation GuideIf you agree with the statement, put an √ beside it. If you disagree with the statement, put an X beside it.   ____ 1. An epoch is larger than a period. ____ 2. Periods are the largest division of geologic time. ____ 3. The smallest period of geologic time is the era. ____ 4. Fossils and rock layers on different continents are similar.

Vocabulary• Copy the definitions below in your notebook on

your definitions page.1. geologic time scale – a model scientists use to

describe the timing of events and the relationships between those events in earth’s history.

2. era – one of three long periods of geologic time from Precambrian to the present.

3. period – geologic time periods that eras are divided into.

4. epoch – a division of geologic time; a subdivision of a period.

Pre-Cambrian

• Began with the formation of the Earth 4.6 billion years ago.

• Bacteria appeared 3.5 billion years ago, followed by algae and fungi.

Paleozoic Era• Divided into 5 periods:• Cambrian period -

Sponges, snails, clams and worms evolve

• Ordovician period - First fishes evolved and other species become extinct

• Silurian period - Land plants, insects and spiders appear

• Devonian period - Amphibians evolve and cone-bearing plants start to appear.

• Carboniferous period - Tropical forests appear and reptiles evolve.

• Permian period - Seed plants become common and insects and reptiles become widespread. Sea animals and some amphibians begin to disappear.

Mesozoic Era• Divided into 3 periods:• Triassic period - Turtles

and crocodiles evolve and dinosaurs appear.

• Jurassic period - Large dinosaurs roam the world. First mammals and birds appear.

• Cretaceous period - Flowering plants appear, mammals become more common, dinosaurs

• become extinct.

Cenozoic Era• Divided into 2 periods:• Tertiary period - First

primates appear and flowering plants become the most common.

• Quaternary period - Humans evolve and large mammals like woolly mammoths become extinct.

ASSIGNMENT

•Read back through the notes you have just taken. Design 4 multiple choice questions about the content.

•

•Design one question which asks for a description or explanation

with details.