Geologic Time

SOME REVIEW FIRST

Fossils can only be found in rocks. sedimentary

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

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

Which is older: F or S How do you know?

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

Intrusions contact metamorphism on all sides

extrusions no contact metamorphism on top

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

H is an intrusion. Contact metamorphism on top

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

A Record of Uplift, Erosion, and Deposition

What processes could lead to an unconformity? weathering and erosion

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

Evolution Explain the theory of evolution. organisms adapt to their environment in order to survive organisms adapt to their environment in order to survive

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

1Approximately how many million years ago did the earliest amphibians appear? Approximately how many million years ago was the initial opening of the Atlantic Ocean? During which era did the earliest fish appear?Paleozoic 4During which epoch did large carnivores appear?Pliocene 5Of the following rocks which would be most likely to contain fossils? a. rhyoliteb. basaltc. metaconglomerated. limestone limestone (it’s sedimentary) 6At Binghamton, NY what is age of the bedrock?Devonian ( million years) 7How does the age of the bedrock at Old Forge compare with that at Jamestown?Jamestown is younger 8Name a location in NY State where you may be able to find bedrock which was formed at the peak of the eurypterid’s development. Silurian age bedrock: Niagara Falls, Syracuse 9Why would fossils be unlikely to be found in quartzite?it’s metamorphic 10For each of the following locations in NY State below, identify whether fossils would be likely or unlikely: Old Forge; Binghamton; Albany Old Forge: unlikely Binghamton: likely Albany: likely

Basic Atomic Structures Dating with Radioactivity  Orbiting the nucleus are electrons, which are negative electrical charges.  Atomic number is the number of protons in the atom’s nucleus.  Mass number is the number of protons plus the number of neutrons in an atom’s nucleus.

Radioactivity Dating with Radioactivity  Radioactivity is the spontaneous decay of certain unstable atomic nuclei.

Half-Life Dating with Radioactivity  A half-life is the amount of time necessary for one-half of the nuclei in a sample to decay to a stable isotope.

Radioactive Isotopes Frequently Used in Radiometric Dating

Example Radioactive isotope = Uranium, Stable Isotope= Lead

Half-life Tips Radioactive IsotopeCircumstance to Use Carbon-14Anything organic or of relatively recent origin PotassiumFor rocks more than 70,000 years in age Uranium-238Relatively middle-aged rocks Rubidium-87A rock of ancient origin

Dating with Carbon-14  Radiocarbon dating is the method for determining age by comparing the amount of carbon-14 to the amount of carbon-12 in a sample. Dating with Radioactivity  When an organism dies, the amount of carbon-14 it contains gradually decreases as it decays. By comparing the ratio of carbon-14 to carbon-12 in a sample, radiocarbon dates can be determined.

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

If there is a 100g sample of C 14, how many grams of C 14 would remain after three half-lives? How long would this take? Show all work. 100g50g25g12.5g    3 half-lives x (5.7 x 10 3 ) =1.71 x 10 4 = 17,100 years