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Put these big events in history in order: dinosaur extinction, first life, formation of oxygen atmosphere, Earth forms, first "man" hominids show up
1. Earth forms 2. first life 3. formation of oxygen atmosphere, dinosaur extinction, first "man" hominids show up
What are the 4 main divisions of geologic time?
Precambrian, Paleozoic, Mesozoic, Cenozoic
What was the dominant life in precambrian time?
cells
What was the most dominant life in paleozoic time?
fish, aquatic life
What was the most dominant life in the mesozoic time?
dinosaurs, reptiles
What was the most dominant life in cenozoic time?
mammals
How do we measure absolute age?
radiometric dating/radioactive decay
What is radiometric dating?
comparing number of unstable parent isotopes in a rock to the stable daughter isotopes
What ages of objects does Carbon-14 best date?
less than 70,000 years
Why do we use radioactive decay to determine the absolute age of rocks?
because decay happens at a fixed rate
What is a half-life?
the time it takes for half of a radioactive parent isotope to decay into a stable daughter isotope
How much parent isotope remains after one half-life? How much parent isotope remains after two half-lifes?
one half of the original amount, one fourth of the original amount
What is the difference between a parent isotope and a daughter isotope?
parent isotope is unstable/radioactive, daughter isotope is stable
What is relative age?
the age of rock layers compared to other rock layers - it can tell if the rock layers are older or younger, but not the exact age
What is the law of superposition?
the oldest layer of rock is on the bottom, the youngest layer of rock is on the top
What is the law of crosscutting relationships?
faults and igneous intrusions (rocks) are younger than the rocks they cut through
Rock Strata Example - List layers from oldest to youngest.
C, B, A, D, E
the igneous intrusion would be younger than the sedimentary rock
What geologic law applies when determining the relative age of rock that cuts through other rock?
law of crosscutting relationships
You have 50mg of a radioisotope with a half-life of 12 minutes. How much of the original sample is left after 24 minutes? How many half-lives have passed after 24 minutes?
12.5mg is left after 24 minutes, 2 half-lives have passed
Potassium-40 has a half life of 1.25 billion years. If you have 16 grams of Potassium-40, how much will you have after 5 billion years?
5 (billion years) / 1.25 (billion years) = 4, which means the Potassium-40 will go through 4 half-lives in 5 billion years - 16 > 8 > 4 > 2 > 1 = 1g
Uranium-238 has a half-life of 4.5 billion years. Its daughter isotope is Lead-206. If you find a rock that has 10g of Uranium-238 and 70g of Lead-206, how old is it?
10g+70g=80g, which means it used to be 80g of Uranium-238 total - reduce the 80 to 10 - 80 > 40 > 20 > 10 - this means the Uranium-238 went through 3 half-lives - 3 (half-lives) x 4.5 (billion years) = 13.5 billion years
Why is Carbon-14 not useful to age dinosaur fossils?
Because dinosaur fossils are too old
Uranium-235 has a half life of 704 million years. If you have 100g of Uranium-235, how long will it take to reach 12.5g?
Reduce 100g to 12.5g - 100 > 50 > 25 > 12.5 = 3 half-lives - 3 (half-lives) x 704 (million years) = 2.1 billion years [3 x 704,000,000 = 2,112,000,000]
Rock Strata Example - List layers from oldest to youngest
M, K, J, I, H, L, G, F, E, D, C, B, A