Chapter 21 Science Vocabulary

Front 1

Which type of fossil can be used for relative dating?

Back 1

Index fossils

Front 2

What is a varve?

Back 2

Bands of alternating light-and dark-colored sediments of sand, clay, and silt.

Front 3

Contrast relative-age dating and absolute-age dating.

Back 3

Relative-age dating compares past geologic events based on order of strata in the rock record.

Front 4

Define evolution.

Back 4

The change in species over time.

Front 5

What are altered hard parts?

Back 5

The soft organic material decays quickly. The remaining hard parts can become fossils with altered hard parts.

Front 6

What is original preservation?

Back 6

The remains are altered very little. They require extreme circumstances, such as freezing, arid, or oxygen-free environments.

Front 7

Describe recrystallization.

Back 7

A buried hard part is subject to changes in temperature and pressure over time. (similar to mineral replacement.)

Front 8

Compare and contrast a mold and a cast.

Back 8

A mold is a fossil that forms when a shelled organism decays in sedimentary rock and is removed by erosion or weathering, leaving a hollowed-out impression. A cast is formed when an earlier fossil of a plant or animal leaves a cavity that becomes filled with minerals or sediment. They are the same because neither of them contain any original or altered material of the original organism.

Front 9

Describe how the fossil record helps scientists understand Earth's history.

Back 9

They provide evidence of the past existence of a wide variety of life forms; most of which are now extinct. It provides evidence that species have evolved.

Front 10

What are trace fossils?

Back 10

Trace fossils are fossils that can provide information about how an organism lived, moved, and obtained food.

Front 11

Compare and contrast the use of U-238 and C-14 in absolute-age dating.

Back 11

You use U-238 to date inorganic materials, and C-14 with organic materials. You would use U-238 to date a rock that's hundreds of millions of years old. (Because it has a longer half-life.) C-14 has a much shorter half-life than other isotopes. You would use C-14 for younger artifacts.

Front 12

Explain how radioactive decay can provide more accurate measurements of age compared to relative-age dating.

Back 12

The rate of radioactive decay is constant regardless of pressure, temperature, or any other physical changes, scientists use it to determine the absolute-age of the rock or object in which it occurs.

Front 13

What is the link between uniformitarianism and absolute-age dating.

Back 13

elements decay today at the same rate that they always have.

Front 14

Describe the usefulness of varves to geologists who study lake deposits.

Back 14

The alternating bands of sediment in varves help scientists date the cycles of deposition in glacial lakes.

Front 15

What is dendrochronology?

Back 15

The science of using tree rings to determine absolute age.

Front 16

What is radiocarbon dating?

Back 16

In radiocarbon dating, scientists use C-14 to determine the age of organic materials, which contain abundant carbon.

Front 17

What is a half-life?

Back 17

The length of time it takes for one-half of the original isotope to decay.

Front 18

Describe radiometric dating?

Back 18

When scientists date an object using radioactive isotopes, they are using radiometric dating.

Front 19

What is radioactive decay?

Back 19

The emission of radioactive particles and the resulting change into other isotopes over time.

Front 20

What was James Hutton known for?

Back 20

He was a scottish scientist who thought that the Earth was much older than 4,000 years.

Front 21

How do geologists determine the relative ages of rock sequences?

Back 21

With original horizontality, superposition, cross-cutting relationships, and inclusions.

Front 22

What are disconformities?

Back 22

They form when a horizontal layer of sedimentary rock overlies another horizontal layer of sedimentary rock, the eroded layer is a disconformity.

Front 23

What is a nonconformity?

Back 23

They form when a layer of sedimentary rock overlies a layer of igneous or metamorphic rock, such as granite or marble, the eroded surface uneven. It indicates a gap in the rock record, during which the rocks are uplifted, eroded at Earth's surface, and new layers formed on top.

Front 24

Angular unconformity

Back 24

Layers of sedimentary rock are deformed during mountain building.

Front 25

Explain how geologists use fossils to understand the geologic history of a large region.

Back 25

The fossils indicate similar times of decomposition even though the layers might be made of entirely different material.

Front 26

Describe original horizontality.

Back 26

The principle that sedimentary rocks are deposited in horizontal or nearly horizontal layers.

Front 27

Describe superposition.

Back 27

As layers are layed upon Earth, the older ones will be on the bottom, with the youngest on the top, unless something happens to change it.

Front 28

What are cross-cutting relationships?

Back 28

States that an intrusion is younger than the rock it cuts across.

Front 29

What is the principle of inclusions?

Back 29

The fragments (inclusions), in a rock layer must be older than the rock layer that contains them.

Front 30

Explain how fossil correlation can be used in geographically distant locations.

Back 30

Fossils can indicate similar times of deposition even though the layers might be made of entirely different material.

Front 31

What is a key bed?

Back 31

A rock or sediment layer used as a marker.

Front 32

What is a correlation?

Back 32

The matching of unique rock outcrops or fossils exposed in one geographic region to similar outcrops exposed in other regions.

Front 33

What is relative-age dating?

Back 33

A way to study the order in which geologic events occurred

Front 34

Explain why the geologic time scale is divided into eras and smaller divisions.

Back 34

They depend on the rock and species present at a certain time period.

Front 35

Name the geologic time divisions from largest to smallest.

Back 35

Eon, era, period, epoch.

Front 36

Why do scientists know more about the Cenozoic than they do about any other era?

Back 36

There has been less erosion, because it is the most recent era.

Front 37

Why do scientists know so little about Precambrian Earth?

Back 37

The organisms were soft-bodied, and therefore difficult to preserve-they wore away. The periods of the Precambrian were long.

Front 38

What is the oldest era of the Phanerozoic eon?

Back 38

Paleozoic. The order from oldest to youngest-- Paleozoic, Mesozoic, then the Cenozoic.

Front 39

What is the importance of extinction events to geologists.

Back 39

When something extincts, something else appears.

Front 40

How long do periods generally last?

Back 40

10,000,000 years or so.

Front 41

How long do epochs generally last?

Back 41

100,000 to 1,000,000s of years

Front 42

How long do eras generally last?

Back 42

10,000,000 to 100,000,000s of years

Front 43

What is mass extinction?

Back 43

When many groups of organisms disappear from the rock record at the same time.

Front 44

what is the purpose of the geologic time scale?

Back 44

The geologic time scale enables scientists to find relationships among the geologic.

Front 45

Geologic time scale

Back 45

A record of Earth's history from its origin (4.6 billion years ago.) to the present.

Front 46

Precambrian

Back 46

The 3 earliest eons make up 90% of geologic time... known together as Precambrian.