Geologic Time & Earth's History

are basically the same as they were in the geologic past

The geological processes that shape Earth's features today _____.

James Hutton

What scientist is credited with proposing the principle of uniformitarianism?

younger than the rocks into which it intrudes

According to the principle of cross-cutting relationships, an intrusive rock body is _____.

remains or traces of prehistoric life

Fossils are the _____.

sedimentary rocks

In what type of rocks are most fossils found?

altered remains

Petrified wood is an example of what type of fossil?

sedimentary rocks

In what type of rocks would geologists most likely find evidence of past life forms?

uniformitarianism

The physical, chemical, and biological laws that operate today have also operated in the geologic past. This statement relates to the principle of ____.

older than the one above it

In general, the law of superposition states that in an undeformed sequence of sedimentary rocks, each layer is ____.

the sandstone

If a layer of sandstone is in contact with a mass of granite that contains small pieces of the sandstone, which rock is older?

angular unconformity

What type of unconformity consists of tilted sedimentary rocks that are overlain by younger, more flat-lying sedimentary rocks?

the conditions under which the organism died and how it was buried

What determines the type of fossil that is formed?

rapidly buried by sediments

Organisms with hard parts stand a good chance of being fossilized if they are ____.

fish

Which of these organisms would have the best chance of becoming part of the fossil record?

4.6 billion years

What length of time does the geologic time scale cover?

eon

The largest expanse of time on the geologic time scale is the _____.

Phanerozoic

Which eon of the geologic time scale means "visible life"?

break apart

Radioactivity is produced when unstable nuclei ____.

the half-life

The time it takes for 50% of the nuclei in a radioactive sample to decay to its stable isotope is called ____.

a date for when the rock formed

The radiometric dating of an igneous rock provides ____.

carbon-14 and carbon-12

Which two substances do geologists use in radiocarbon dating?

geologic time scale

Based on interpretations of rock units and changes in fossil life forms, geologists have divided Earth's history into manageable units that are represented by the ____.

about 4.6 billion years old

What is the currently accepted age of Earth?

Paleozoic

The era of "ancient life" is known as the ____.

540 million years ago

When did abundant fossil evidence appear in the geologic record?

Gondwana

During the early Paleozoic era, South America, Africa, Australia, Antarctica, India, and perhaps China comprised the vast southern continent of _____.

They fused into Pangaea.

What happened to all the continents by the close of the Paleozoic?

seas

In the early Paleozoic, life was restricted to the _____.

Dinosaurs

What animals dominated the Mesozoic Era?

birds

One group of reptiles, characterized by the fossil Archaeopteryx, led to the evolution of _____.

a meteorite collision

What likely contributed to the extinction that marks the end of the Mesozoic Era?

Quaternary

Which period represents the last 2 million years of geologic time?

plate interactions

What caused many events of mountain building, volcanism, and earthquakes in western North America during the Cenozoic?

age of mammals

Which title best describes the current geologic age?