determining ages of rocks

Question 1

age of rock compared with the ages of other rocks

Answer 1

relative age

Question 2

number of years since the rock formed

Answer 2

absolute age

Question 3

in horizontal sedimentary rock layers the oldest layer is a the bottom; each layer higher is younger that the layer below it

Answer 3

Law of Superposition

Question 4

magma that cools and hardens into a mass of igneous rocks beneath the surface

Answer 4

intrusions

Question 5

break in Earth’s crust which is always younger than the rock cuts it through

Answer 5

fault

Question 6

gap in the geological record where some rock layers have been lost because of erosion

Answer 6

unconformity

Question 7

all of the atoms of a particular type of matter are the same

Answer 7

element

Question 8

process by which one unstable element breaks down into another element that is stable

Answer 8

radioactive decay

Question 9

time required for half of the unstable element to decay

Answer 9

half-life

Question 10

represent a type of organism that existed only briefly in order to help geologists tell the relative ages of the rock layers in which they occur

Answer 10

index fossils

Question 11

used to determine the absolute age of rocks, by first determining the amount of a radioactive element in a rock

Answer 11

radioactive dating

Question 12

Why do geologists study index fossils?

Answer 12

It helps geologists tell the relative ages of the rock layers.