Relative Time

Fossils and rock layers

Remind me again…

What is the

difference

between a

timeLINE

and a

timeSCALE?

Remind me again…

What is the difference

between relative-age

dating and absolute-age

dating?

What is a fossil?

Fossil: The trace or

remains of an organism

that lived long ago.

Are all organisms

preserved as fossils?

There are three types

of rocks, do you

remember their

names?

Which type of

rock do you

think most

fossils are

preserved in?

Why?

If fossils are organisms of the

past, how can they help us tell

about the history of the earth?

Index Fossils

A fossil that is found in the

rock layers of only one

geologic age

They are found in rock

layers around the world

For example: Which fossil is a good index

fossil?

Rock Layers

Almost one half (approximately 2 billion years) of earth’s history can be seen at the Grand Canyons National Parks

through the different rock layers found there

It is one of the best places in America to see this

much history

If you’re looking at a rock

sample, which layer would be

the oldest?

This is the law of SUPERPOSITION: in sedimentary rock

layers, the rocks are laid out fairly flat, where the oldest is on

the bottom and the youngest is on the top.

If nothing disturbs the rock layers they will

remain the same. If the rock layers are

disturbed, they may end up like this:

What things that can disturb rock layers?

•Folding or tilting from shifting plate tectonics

•Volcanic intrusions

•Faults

Volcanic Intrusions

Faults and plate tectonics

UNCONFORMITY

An unconformity is a gap in the

geologic record.

How could this happen?

Lets practice…

Lets practice…

How about a harder one?