SHS Geologic Time

an erosional surface between horizontal sedimentary rocks

A disconformity is ___________ .

older --- younger

An undeformed sedimentary layer is __________ than the layer above and _______ than the layer below.

300,000 years

Atoms of AA decay to atoms of BB with a half-life of 100,000 years. If there are 20,000 atoms of AA to begin with (and 0 atoms of BB), how long will it take for there to be 2,500 atoms of AA?

sedimentary

Fossils are most common in which rock types

more

In the past there were (more or less) atoms of radioactive Uranium?

Paleozoic

Land plants appeared during the

Mesozoic

Large reptiles became abundant during the ________Era?

Cenozoic

Mammals became abundant during the ________Era?

sedimentary

Radiometric dating is least useful for ___________ rocks.

Jurassic

The Paleozoic does not include the

Mesozoic

The _________ was an era dominated by the dinosaurs

eras

The boundaries between _______ seem to coincide with major changes in the life forms present on Earth.

sediments are deposited as essentially horizontal layers

The principal of original horizontality states that ________ .

uranium-238

The radon environmental hazard is associated with the radioactive decay of ______ .

matching of similarly-aged rocks from different outcrops

The study of faunal succession allows ___________

the Paleozoic

What era of geologic time ended with the largest extinction event in Earth history?

an eon

What is the longest division of time in the geologic time scale?

angular unconformity

What is the name for an erosion surface that separates two sets of sedimentary layers with non-parallel bedding planes?

an epoch

What is the shortest division of time in the geologic time scale?

radiometric dating

What scientific avenue of investigation gave scientists the best estimate of the age of the Earth?

all of these

Which of the following is used by geologists to determine the relative ages in a rock sequence?

carbon-14

Which of the following radioactive isotopes is most useful for dating a very young sample (<20,000 years) of wood?

Precambrian

Which of the following represents the longest time period

decomposed organic material

Which of the following will not make a fossil?

nonconformity

a gap in the geologic record bounded below by metamorphic or igneous rocks and bounded above by sedimentary rocks