Section 3.1• Vocabulary to know: • James Hutton

• Uniformitarianism• Catastrophism• Charles Lyell

James Hutton’s New Idea• Came up with a

theory in 1788…– Uniformitarianism

• Geologic processes happening today also happened in the past

• Seems obvious, but actually sparked controversy

Catastrophism Vs Uniformitarianism

• Not everyone liked Hutton’s ideas…

• Catastrophism:– States that geologic

change occurs suddenly

• Uniformitarianism lost the debate until Charles Lyell proved Hutton to be right…kinda…

A Happy Medium• Most geologic

processess follow Hutton’s theory of uniformitarianism…

• But sometimes Catastrophism does occur– Asteroids

• Meteor Crater in Arizona

Section 3.2• Vocabulary to

know:• Relative age• Law of

Superposition• Principle of

horizontality• Principle of cross-

cutting relations• Index fossil

What is their age?

??????????• Don’t know their

absolute age• Relative age-

– The age of an event or object (person) in relation to other events or objects (people)

– In other words, you put things in order oldest to youngest…• …Or youngest to

oldest

What can we learn about time from this picture?

You can learn a lot!• Until the 1900’s we

couldn’t get absolute ages for fossils…

• We had to assign things based on the order that they occurred

• Law of Superposition-– Sedimentary rocks

form in layers– Oldest layers on the

bottom…– …Youngest on the top

Principle of original horizontality• Sedimentary layers are nearly horizontal when deposited… • Those that are not, have been deformed by movements of

Earth’s crust

Principle of crosscutting relations • Geologic features, such as faults, and igneous intrusions

are younger than the rocks they cut through

What’s the oldest layer?

Put these in order from oldest to youngest…

Youngest

_____

_____

_____

_____

Oldest

Index fossils• Index fossil-

– Fossils of organisms that were common, lived in many areas, and existed only during specific spans of time

• Fossil found in specific rock layer MUST have lived during that time

Life cycle of a fossil…

Bad index fossils…Why?

Shark

Crocodile

Section 3.3• Vocabulary to

know:• Absolute age• Atom• Element• Isotope• Atomic number• Atomic mass• Radioactivity• Half-life• Carbon-14 dating

Ok great… But how do we figure out the actual age of fossils?

• Absolute age-– The actual age of

an object or event

• To figure out absolute age you have to take a look at atoms…

• …more specifically, the isotopes of those elements made up of atoms

Absolute

A riddle to show me you understand…• There are two goat

herders… One named Jeremy, and the other named Decker

• Jeremy says to Decker, “Why don’t you give me one of your goats so that we have the same amount?”

• Decker responds with, “No, why don’t you give me one of your goats so that I have twice as many as you?”

• What is the relative amount of goats that each person has?

• What is the absolute amount of goats that each person has?

Atoms• Atom comes from

the Greek word atomos…– …which means:

unable to cut

• Atoms are made up of:– Protons (In the

nucleus)– Neutrons (In the

nucleus)– Electrons

Elements• Element-

– a pure substance that consists entirely of one type of atom

– Make up everything in the universe

– Atomic number- • number of protons.

– Atomic mass- • protons + neutrons.

• Why is it 4.003, and not 4.0?

Isotopes• Isotopes are

identified by their mass number.

• Protons are constant…but sometimes there can be more neutrons than protons.

Radioactivity…• Some isotopes are

unstable– Meaning that they

only exist for a little while before they change (Breakdown) into something else (more stable form)

• Certain isotopes always change (Break down) into something else (more stable form) at the same rate

Use radioactivity as a geologic clock• Half-life-

– Length of time it takes for half of the atoms in a sample of a radioactive element to change from an unstable form into another form

• Different elements have different half-lives– Fractions of seconds– Billions of years

Parent Daughter Half-life (years)

Thorium-232

Lead-208 14 billion

Uranium- 238

Lead- 206

4.5 billion

Beryllium-10

Boron-10 1.52 million

Carbon-14

Nitrogen-14

5715

Half-lives• Rate of change from one element into another is

measured in half-lives• Breaks down at a constant rate

Carbon-14 dating• Live organisms

take in C14

– Half-life = 5730 years

• When an organism dies it no longer takes in C14

• C14 breaks down into N14 at a constant rate

• By measuring the half-life we can figure out when the organism died

Section 3.4• Vocabulary to

know:

• Fossil• Original remains• Ice (Original remains)• Amber (Original remains)• Tar (Original remains)• Sedimentary rock (Fossils)• Molds• Casts• Petrified wood• Carbon films• Trace fossils• Tree rings• Ice core

How do we know about the past?• Rocks and fossils!• Fossil-

– Traces or remains of living things from long ago…

• Fossils exist in many forms-– Hard animal remains

(shells, bones, teeth, etc.)

– Impressions on rock– And sometimes…

You actually find the organism• Original remains-

– Fossils that are the actual bodies or body parts of organisms

– Found in substances that keep out air and tiny organisms

• Very important because they give DIRECT evidence that is undisputable

How are original remains preserved?• Ice-

– Ice fields in Siberia and Alaska contain 10,000 year old mammoths and rhinos

– Bones, muscle, skin, and even hair in place

How are original remains preserved?• Amber-

–Tree sap traps insects within it

–Tree gets buried and this sap turns into amber

How are original remains preserved?• Tar-

–La Brea tar pits trapped animals from the past

–Saber-toothed cats and other animals have been preserved

How do fossils form?• The organism must

be preserved before it decomposes– Hard parts (bones,

teeth, tree trunks, etc) decompose slowly

– Soft parts (muscles, skin, etc) decompose fast

• Most fossils are the hard parts of organisms

Where do rock fossils form?• Sedimentary rock-

– Formed from sediments being compacted and cemented together

• Sometimes the sediment builds up around plant or animal remains

• If sedimentary rocks are changed by heat and pressure…

• …the fossil is usually destroyed

Fossils in rocks• Molds-

– A visible shape that was left after an animal or plant became buried in sediment and then decayed away

• Casts-– When a mold

becomes filled with minerals and preserves the shape of the original organism

Fossils in rocks• Petrified wood-

– Tree is covered in sediments…– …water with minerals seeps into

the tree…– …minerals end up producing a

“cast” of the tree• Carbon films-

– Sometimes the Carbon from an organism is left behind as a visible layer

• Trace fossils-– Not parts or an impression of an

animal, but some other evidence• Ex: footprints

How do we know what the environment was like in the past?

• Tree rings-– Width of the tree ring

depends on how much the tree grew that year

– Thin ring = dry year– Thick ring = wet year

• Lot’s of growth during wet years

• Ice cores-– Analyze air trapped within

the ice to see how the atmosphere has changed

– Can test ice from as far back as 530,000 yrs ago