How do we know what happened millions of years ago? Geologic Time How do we know what happened millions of years ago?

never lived at the same time Why is this statement false: “The caveman had dinosaur for breakfast.”? man and dinosaurs never lived at the same time

Fossils can only be found in rocks. sedimentary

Relative Dating Determining the age of rocks or events in relation to the age of other rocks and rock forming events

Principal of Original Horizontality Rocks form in horizontal layers parallel to earth’s surface. These layers are known as STRATA

Deformed or Distorted Layers Rocks that no longer show original horizontality

Folded Strata

Faulted Strata

Tilted or Uplifted Strata

Relative Age If a sedimentary rock outcrop has not been overturned, which layer would be the oldest?

Principle of Superposition oldest rock layers are on bottom Rocks get younger as you move up towards the surface

Using this principle, label the strata below from oldest to youngest.

Law of cross cutting relationships Rocks are older than any fault, intrusion, or other feature that cuts across them

there first (it's older) Which is older: F or S How do you know? S= rocks F= fault F cuts through S S must have been there first (it's older)

Faults are always (older, younger) than the rocks they cut through.

Put these in order from oldest to youngest

When magma squeezes into pre-existing rocks and crystallizes Igneous intrusions & extrusions When magma squeezes into pre-existing rocks and crystallizes What happens when magma touches rocks??

Put these in order from oldest to youngest

Put these in order from oldest to youngest

Put these in order from oldest to youngest

If a geologist finds an igneous sill, how can she determine if the sill is an intrusion or an extrusion?

contact metamorphism on all sides Intrusions contact metamorphism on all sides

no contact metamorphism on top extrusions no contact metamorphism on top

Is “H” an intrusion or extrusion? How can you tell?

H is an intrusion. Contact metamorphism on top

a buried erosional surface What is an unconformity? a buried erosional surface How does it complicate the relative dating of rock layers? a part of the rock record is missing

weathering and erosion Animation!! What processes could lead to an unconformity? weathering and erosion Animation!!

Using the diagram to the left, identify where the unconformity is located by drawing an arrow and writing the word “unconformity” next to it.

Put these in order from oldest to youngest X Put these in order from oldest to youngest

Z X Y

What do fossils tell us about Earth’s History?

What characteristics must fossils have in order to be good index fossils? lived over a large geographic area (large horizontal distribution) lived for a short period of time (small vertical distribution)

In geology, this is referred to as CORRELATION In the diagram below, a geologist has matched up rock layers based on index fossils.

Evolution a developmental process in which an organ or organism becomes more and more complex by differentiation of its parts Natural selection- (Survival of the fittest) only the organisms best adapted to their environment tend to survive and transmit their genetic characters in increasing numbers to succeeding generations while those less adapted tend to be eliminated

Evolution can see that different organisms have changed over time Explain how the fossil record supports this theory can see that different organisms have changed over time

ESRT Page 8 & 9

Using pages 8 & 9 of the ESRT’s Answer the questions starting on page 6 in your notes

Absolute Age The actual age of a fossil or rock layer How is it determined? Radio-active dating

their half-lives are constant Absolute Age Why are radioactive isotopes useful in determining the absolute age of a rock? their half-lives are constant

NOTHING! it is reliable to calculate age Absolute Age What can be done to change the half-life of a radioactive isotope? Why is this important? NOTHING! it is reliable to calculate age

Half Life The amount of time needed for HALF of the radio-active element to decay The Half-life NEVER changes Page 1 of the ESRT’s

We use a ratio between parent to daughter will tell you how many half-lives have gone by.

One half-life. 50% parent 50% daughter 1 half life

Two half-lives. 25% parent 75% daughter 2 half lives

Three half-lives. 12.5% parent 87.5% daughter 3 half lives

Four half-lives. 6.25% parent 93.75% daughter 4 half lives

How many half lives does there will always be some trace amounts left Absolute Age How many half lives does it take to get to 0%? We will never get to 0% there will always be some trace amounts left

stable atoms unstable atoms Draw the generic graph for the half-life of a radioactive isotope. stable atoms unstable atoms

carbon-14 What radioactive isotope could be Absolute Age What radioactive isotope could be used to determine the absolute age of material that was recently living? carbon-14

Carbon 14 Decays into Nitrogen 14 Used to find the age of living organisms within the last 50,000 years 1 HL= 5,700 years 2HL= 11,400 years 3 HL= ?????

Potassium 40- Used for old rocks Known as K 40 Turns into Argon 40 Dates rocks 1 HL= 1.3 Billion years 2 HL = 2.6 Billion years 3HL = ???????

Uranium 238- used for REALLY old rocks U-238 turns into Lead 206 Used to find the age of the oldest rocks 1HL = 4.5 Billion Years 2 HL= 9.0 billion years Can we find a rock that has gone through 2 Half lives?????

3 half-lives x (5.7 x 103) =1.71 x 104 = 17,100 years If there is a 100g sample of C14, how many grams of C14 would remain after three half-lives? How long would this take? Show all work. 100g  50g  25g  12.5g 3 half-lives x (5.7 x 103) =1.71 x 104 = 17,100 years