Describing ages of rocks
Define Relative
Compared to
True or False
Scientists use multiple ways to determine relative age
What are the preserved traces or remains of living things called.
fossils
Define absolute age
The age something actually is or how long it has been since something first formed.
What percent of earths history is taken up by the precambrian time period
88%
Define relative age
The age of something compared to the age of something else.
when undisturbed, older rocks are on the bottom and younger rocks are on top.
This is the law of __________________
Superposition
Define index fossils
Fossils of animals that were all over the place but lived relatively short time in history.
What word means "The time is takes for half of an unstable element to decay"
Half life
Define refine
to make better
Define absolute age
The actual age of something or the age of something since it was first created
What is it called when molten/lava forms new rocks on the outside/on top of other rocks.
Igneous extrusion
Name the most likely reason that rocks that are the same age could be on top of each other
folding
What word/words means to determine the absolute age of a rock by using the half lives of its atoms.
Radioactive dating
Eras
Describe the difference between relative age and absolute age
Relative age is comparing the ages of multiple things and absolute age is how old something is
Describe the difference between an igneous intrusion and an igneous extrusion.
Igneous intrusions are when lava cuts through and forms new rock inside of other rocks. Igneous extrusions are when lava forms new rock outside/on top of other rocks.
What word means a gap in the geological record because rocks have eroded away
unconformity
Define radioactive decay
When an atom breaks down and form another element.
what are the subdivisions of eras on the geological time scale called.
periods
Why do geologists want to analyze and describe the ages of rocks?
Evidence of past events occurs in rocks.
Describe the age of a fault relative to the rocks around it.
The fault is younger than the rocks around it.
Describe how geologists use index fossils to determine the relative age of the things around them
They know that the things around index fossils are the same age and lived in the same time as the index fossils.
If a rocks isotope has a half life of 100 years, and the rock contains 25% of the isotope still, how old is the rock.
200 years old
Name the 3 eras on the geological time scale
Mesozoic, paleozoic, cenozoic