Geology and Earth's History...

The Age of Enlightenment: End of the 18th century (1700’s) People began to look to science for answers: How old is the Earth? How was it formed? New ideas were wearing down traditional ideas

The Age of Enlightenment: Beliefs of that time: Earth was several thousand years old Earth’s features (mountains, canyons, etc) were caused by rare but quick impacting catastrophes

James Hutton (1726-1797) Scottish Lawyer Became a doctor Successful farmer Interested and studied Earth’s processes

James Hutton Found areas of granite in sedimentary rocks of Scotland Viewed as evidence of heat beneath the surface Decided that Earth’s core made new rock

Hutton’s drawing and the rock that inspired it at Siccar point James Hutton Found unconformities Areas where layers are not in neat rows lower layers must have been there long ago, then later moved or pushed up Evidence of long periods of time in earth's history. Hutton’s drawing and the rock that inspired it at Siccar point Photo obtained at: http://honolulu.hawaii.edu/distance/gg101/Programs/program12%20Geologic%20Time/program12.html

James Hutton Uniformitarianism What we see changing the Earth today must be the same as what changed the Earth in the past "Theory of the Earth; or an Investigation of the laws observable in the composition, dissolution, and restoration of land upon the globe." Transactions of the Royal Society of Edinburgh, 1788, 1:209-304

Earth’s Geological Processes Uniformitarianism: Processes shaping the earth (erosion, deposition, mountain building etc.) do not change over time but remain uniform Catastrophism: All geologic processes (locally and globally) occur suddenly due to violent changes in the Earth vs. Today we see that both cause changes to the earth.

Words to know… Fossils: remnants of past life/living things; mostly remnants of hard things Paleontology: the study of fossils teaches us about changes to life on Earth integrates Biology and Geology

How do geologists know how old rock is? Law of Superposition: in undisturbed areas, younger rocks lie above older rocks Relative Dating: comparing layers of rock to determine the order of formation Relative Time: time based upon relationships in rock layers; relative order of events

Given the colored “rock” layers: * Which layer is oldest? Relative Dating Given the colored “rock” layers: * Which layer is oldest? * Is the green rock older or younger than the pink rock?

But............... Sometimes things don’t happen uniformly Geologic Column can help identify the relative age of rock layers. Diagram from: http://www.nwcreation.net/geologycolumn.html

What’s the order?

Stratigraphy Complete the Stratigraphy document find the relative age of the layers in the rock sequences!

Absolute Dating: A Measure of Time...

Establishing the age of an object in numbers of years Absolute Dating... Establishing the age of an object in numbers of years Uses radioactive or radiometric dating

T. W. Richards, 1913: found two atomic masses for lead. F. W. Aston, In 1919: separated neon atoms into two different isotopes Invented the mass spectrograph Today: many isotopes of the elements have been discovered.

Radioactive elements are unstable and change to become stable Radiometric Dating Radioactive elements are unstable and change to become stable Measuring the amount of breakdown of radioactive atoms in rocks to determine age Unstable Isotope Aka “Parent” Stable Isotope Aka “Daughter”

In this compound, are all the atoms of a given element exactly the same? Isotopes of an element have the same chemical properties but different atomic weights.

Isotopes Isotopes - Different forms of an element having the same number of protons but different numbers of neutrons (and therefore different atomic weights).

Naturally occurring chemical elements are usually mixtures of isotopes, and so their atomic masses are weighted averages of the masses of the isotopes in the mixture.

Radioametric Dating Half-Life- time it takes for 1/2 of the radioactive atoms to decay into a stable isotope Rate of breakdown is constant Unstable isotope is Parent Material; Stable material produced after decay is Daughter Material

Radioametric Dating Living things have a constant ratio of C-14 to C-12 Dead things have their C-14 begin to decay Half-life for C-14 is 5,730 years Carbon-14 is mainly used for things up to 50,000 years old

Radioametric Dating Half-life for C-14 is 5,730 years If you have 12 grams of C-14, how long will it take for the parent material to decay into 6 grams? If you have 24 grams of C-14, how much parent material will be left after 5,730 years?

Half Life Ratios 1 half life = ½ radioactive 2 half lives = ¼ radioactive 3 half lives = 1/8 radioactive 4 half lives = 1/16 radioactive

DIRECTIONS Set up a table for the problems that includes Time, Unstable Amount, and Stable Amount Example: Scientist found a sample of bone and found that 6.25% of the total carbon 14 was left. Determine the age of the bone.

Example: Scientist found a sample of bone and found that 6 Example: Scientist found a sample of bone and found that 6.25% of the total carbon 14 was left. Determine the age of the bone. (C-14 Half-life is 5,730 years) # of Half-lives Time (yrs.) Unstable Stable