Chapter 6 review

1. UNIFORMITARIANISM:

-The processes that shape the Earth today are the same processes that occurred in the geologic past

“The present is the key to the past”

2. ORIGINAL HORIZONTALITY

-Sedimentary rock layers are ALWAYS laid down in horizontal layers, until some other process alters them

-The bottom layer of horizontal sedimentary rock layers is always the oldest, UNLESS the layers have been overturned or have had older rock formed on top of it

*The lower layers must first be in place before the next layer can be deposited

3. SUPERPOSITION

OLDESTOLDEST

YOUNGESTYOUNGEST

Extrusion:When molten rock flows on the Earth’s surface forming an igneous rock

Intrusion:Occurs when magma squeezes

between layers of pre-existing rock beneath the Earth’s surface

-Causes surrounding layers to metamorphose (Contact metamorphism)

FOLDS AND FAULTS

Fold:

-bends in rock layers produced by movements of the earth’s crustFaults:-breaks in the rock where shifting of rock layers has occurred, often associated with earthquakes

Folds and Faults are always

younger than the original

rock layers

-Preserved remains or trace evidence of a plant or animal living in the past

Fossils reveal clues to ancient

environments

Mrs. Sharp

Index Fossils: Fossils that are found geographically widespread and lived fora short period of time

By comparing index fossils in various locations on Earth, it is possible to correlate (match) the relative ages of the rocks in which they appear

““GeographicallyGeographicallywidespread” widespread” means theindex fossils are foundin more than one rock column

Lived for a “short“shortperiod of time” period of time” meansthe index fossils are found in only one layer

What is Correlation?When geologists try to match rock outcrops in different locations to see if they formed at the same time.

How to correlate (match) rock layers: Similarity of rock types Matching index fossils Volcanic ash layers used as time markers

Relative Age of rocks: (sequence)The age of a rock layer in

comparison to its surrounding layer

Absolute Age of rocks: (true age)The age of a rock layer in years

-Uses rock similarity, fossilevidence, and volcanic time markersto determine its order of occurrence

-Uses radiometric dating to determine age--radioactive decay

Radioactive decay is the process bywhich the natural breakdown of unstable atoms of an element occurs, releasing particles and energy (heat), and changes that element’s atoms into anew element

Example: it takes 4.5 billion years for uranium 238 to change into lead 206

Radioactive decay is NOT AFFECTED by temperature (heat) or pressure!

Radioactive decayoccurs at a constantrate known as half-life.

HALF-LIFE:Half-life is the rate (time) it

takes for one-half of the amount of original material to decay

If we know the half-life of a radioactive material, the age of the material can be determined by measuring the amount of

decayed material in the sample.

ESRT pg. 1 Radioactive Decay Data chart

Some radioactive substances have a Short half-life: Carbon 14-Good for dating recent organicremains (between 1,000-50,0000 yrs.)

Uranium238

decays to Lead 206

-Good for dating much older rocks(a very long half-life) - it takes 4.6 billion years for uranium to decay to lead

Long half-life: Uranium238

Example:The amount of Carbon-14

remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount ofCarbon-14 was 2.0 grams.

(2.0g _____ _____) 1.How many half-lives did the sample undergo?

2.Multiply this by the half-life for Carbon-14 (ESRT)

Example:The amount of Carbon-14

remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount ofCarbon-14 was 2.0 grams.

(2.0g 1.0g 0.5g) 1.How many half-lives did the sample undergo?

2.Multiply this by the half-life for Carbon-14 (ESRT) Answer: 2 x 5,700 = 11,400 yrs.

Example:The amount of Carbon-14

remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount ofCarbon-14 was 2.0 grams.

(2.0g 1.0g 0.5g) 1.How many half-lives did the sample undergo? 2

2.Multiply this by the half-life for Carbon-14 (ESRT)

Example:The amount of Carbon-14

remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount ofCarbon-14 was 2.0 grams.

(2.0g 1.0g 0.5g) 1.How many half-lives did the sample undergo? 2

2.Multiply this by the half-life for Carbon-14 (ESRT)

Example:The amount of Carbon-14

remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount ofCarbon-14 was 2.0 grams.

(2.0g 1.0g 0.5g) 1.How many half-lives did the sample undergo? (how many times did it decay) 2 half-lives

2.Multiply this number by the half-life for Carbon-14 (ESRT) Answer: 2 x 5,700 yrs. = 11,400 yrs.