Chapter 17-1 The Fossil Record

Era

One of several subdivisions of the time between the Precambrian and the present

Carbon-14

Only useful for dating fossils younger than about 60,000 years, because it has a short half-life

Relative dating

The age of a Fossil is determined by comparing its place with that of fossils in other layers of rock.

Index fossils

A distinctive fossil used to compare the relative ages of fossils.

After Precambrian time, the basic divisions of thr geologic time scale are eras and periods.

After Precambrian time, what happens on the geologic time scale?

Cenozoic era

Began about 65 million years ago and continues to the present. Mammals became common during this time

By comparing the amounts of carbon-14 and carbon-12 in a fossil. The more carbon 12 there is compared to carbon-14, the older it is.

How can researchers determine when an organism lived?

Relative dating and Radioactive dating

How do paleontologists determine the age of fossils?

Fossil record

Information about past life, including structure of organisms, their diets, what ate them, their environment and the order in which they lived. Provides evidence about the history of life on Earth. It so shows how different groups of organisms have changed over time.

Mesozoic era

Lasted about 180 million years; dinosaurs as. As other kinds of organisms lived during this era

Paleozoic era

Lasted about 300 million years and included many vertebrates and invertebrates (animals with and without backbones)

Geologic Time Scale

Scale used by paleontologists to represent evolutionary time

Paleontologists

Scientists who study fossils

Haf-life

The length of time required for half the radioactive atoms in a sample to decay

Isotopes with longer half-lives and potassium-40

Used to date rocks that are billions of years old

Radioactive Dating

The use of half-lives to determine the age of a sample. Scientists calculate the ad of a sample based on the remaining radioactive isotopes it contains.

Periods

Unit of time into which eras are subdivided

Fossils occur in a particular order and shows that life on Earth has changed over time.

What did the fossil record reveal?

A species must be easily recognized and mist have existed for a short period but have had a wide geographic range

What requirements must be met to be used as an index fossil?

Paleozoic, Mesozoic, and Cenozoic era

What three eras is the geologic time scale divided into?

Precambrian time

What time does the geologic time scale begin with?

Extinction

When a species dies out

Sedimentary rock, which is formed when exposure to rain, heat, wind, and cold breaks down existing rock into small particles of sand, silt, and clay

Where do most fossils form?