Chapter 7 Science: Investigating Rock Strata
A 3 million-year-old igneous layer lies below a sedimentary layer that lies below a 2 million-year-old index fossil. How old is the sedimentary layer?
between 2 and 3 million years old
Radioactive atoms ___________ and form a different kind of atom.
decay
Igneous rocks contain radioactive atoms, so as the rock gets older __________.
fewer radioactive atoms remain
The law of ___________ says that the sequence of changes in organisms as recorded by fossils is the same everywhere on Earth.
fossil succession
What kind of rock does absolute dating work for?
igneous
Which of the following is a feature that is applicable to the law of cross-cutting relationships?
igneous intrusion
Fossils of organisms that lived in a widespread area over a short period of geologic time are called ___________.
index fossils
It is reasonable to guess that rock layers on either side of a gap are the same age because of the principle of ___________.
lateral continuity
What is the name of the law that states that a rock feature cutting across another rock feature is the younger of the two rocks?
law of cross-cutting relationships
Rock layers below are __________ rock layers above.
older than
According to the principle of ____________, rock layers form in ________ layers due to gravity.
original horizontality; horizontal
What is it called when scientists use radioactive atoms to absolutely date igneous rocks?
radiometric dating
If an igneous rock cuts a sedimentary rock in half vertically, which rock is older?
sedimentary
law of superposition
states that in undisturbed rock layers, the oldest rock is at the bottom and the youngest rock is at the top
principle of original horizontality
states that rock layers form when sediments are deposited in horizontal layers due to gravity
principle of lateral continuity
states that sediments are deposited in layers that extend horizontally in all directions until they reach an obstacle
law of cross-cutting relationships
states that the rock feature that cuts across another rock feature is the younger of the two features
law of fossil succession
states that the sequence of changes in organisms as recorded by fossils is the same everywhere the fossils are found on Earth
What can cause rock layers to fold?
tectonic forces
A fault line runs through an igneous intrusion in a sedimentary rock layer. The youngest feature is ___________
the fault line
What are fossils?
the preserved remains of organisms
absolute dating
the process of determining the approximate age of a rock, fossil, or event
relative dating
the process of determining the order in which events in Earth's history occurred
For the law of superposition to hold true, the layers of rock must be _____________.
undisturbed
Why is the Grand Canyon a good place to study rock layers?
Lots of layers have been uncovered by river erosion.
______________ determines the age of a rock by comparing it to the rocks around it.
Relative dating
Rock A has 50% of its uranium atoms remaining, and Rock B has 20% of its uranium atoms remaining. Which rock is older?
Rock B
Why are index fossils important?
They are useful for relative dating of rock strata.
