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?