p. 552 Fossils and the Rock Record
Relative
Time Scale
Visit this United States Geological Survey (USGS) site for a
brief history of the development of the concept of geologic time. You
can read about the activities of William Smith. Scroll down and click
on index fossils, forms of life that existed during limited periods
of geologic time. Name one organism that is an index fossil of the Jurassic
period.
Follow
a Vertebrate Fossil
At this Denver Museum of Nature & Science site you can follow
along to find out what happens to a fossil after its discovery. You
can choose among a plant, an invertebrate, or a vertebrate fossil. Click
on the type of fossil you want to learn more about. Read the first page,
then click next to continue reading about that fossil. This is a great
site if you always wanted to know what paleontologists do!
The
Major Fossil Groups
Go to this USGS site to learn about typical types of fossils.
Fossils are grouped here by primary habitat, either terrestrial (land)
or aquatic (water). Under the terrestrial group, click on Spores and
Pollen. Why are spores and pollen important fossils?
Frequently Asked Questions about Paleontology
You can find answers to many questions about fossils and paleontology
at this site by the University of California Museum of Paleontology.
If you would like to look for fossils yourself, you can find out how
to locate fossils by scrolling down to find the answer to this question.
Are there any accessible sites for fossil hunting in your area?
p. 555 The Geologic Time Scale
Geologic
Time
At this USGS site you can learn more about the age of Earth
and the history of human thought about Earth’s age. Read the page then
click on Next to continue the story. Who was the first person in recorded
history to suggest that changes occur on Earth over time?
Global Earth History
This is a good site for those who are interested in how plate tectonics
affected the geologic time scale. The site by Northern Arizona University
contains a series of plate tectonics reconstructions to show the broad
patterns of Phanerozoic Earth history. You can see vertical or horizontal
slices through geologic time periods. Scroll down and click on Permian,
then on paleogeographic globes at 270 mya (millions of years ago) to
see what the continents looked like at that time.
Radiometric
Time Scale
Go to this USGS site to learn how radioactivity is used to date
rocks and their associated fossils. The most common isotopes used to
date ancient rocks are uranium-235, uranium-238, thorium-232, rubidium-87,
potassium-40, and samarium-147. These isotopes are used for dates into
the billions of years. What isotopes can be used for measuring thousands
of years?
How
Carbon-14 Dating Works
Although this is a commercial site, it has good information
on how carbon-14 is used to date relatively young (less than 50,000
years old) fossils and artifacts. Read the text then click on Next Page
to find out how carbon-14 is made. What is the half-life of carbon-14?
How does this help date a fossil?
The
Geologic Time Scale
Visit this USGS site for a good chart showing the eras, periods,
and epochs of the geologic time scale. Scroll down to read descriptions
of each time period. Dinosaurs lived during the Cretaceous period. Where
did this time period get its name?
Geologic
Time Scale
At this Geological Society of America site you can see a much
more complex geologic time scale. This time scale includes further divisions
(ages) that paleontologists use for identifying fossils.
Natural History Highlight: Geologic
Time Scale
Visit the Smithsonian Institution’s National Museum of Natural History
site for another version of the geologic time scale. During which epoch
did modern types of flowering plants appear?
p. 564 The Oldest Rocks
Park
Geology Tour of the Oldest Rocks
At this National Park Service site you can take a tour of the
oldest rocks found in the national parks of the United States. Precambrian
rocks can be found in both the eastern and the western national parks
and monuments. Click on Grand Teton National Park, then on park geology,
to find out more about the rocks found in this park. How old are the
oldest rocks in Grand Teton National Park?
Fossils
and Rocks
This is an online book from the USGS. This site tells the history
of using fossils to identify rocks of the same age found in different
places on Earth. Click on Next at the bottom of the page to go on. What
three concepts are important in the study and use of fossils?
Dendrochronology
At this site you can find a more detailed description of dendrochronology,
the dating of past climatic events through the study of tree rings.
Dendrochronology began early in the 20th century. Scroll
down and read about the age of bristlecone pine trees in the White Mountains
of California. How old are these trees?
The
Laboratory of Tree-Ring Research
Visit this University of Arizona site to learn more about dendrochronology.
Click on the bar with tree rings at the top of the page to learn about
tree rings. Why is counting the number of tree rings not enough to identify
a tree’s age?
p. 572 Members of Proboscidea
The Mammoth Site
Visit this site to learn more about mammoths and their relatives. Take the virtual tour of the museum. What are some of the other animals that lived during the time of the mammoth?
Proboscidea
Through Time
Go to this site by the Illinois State Academy of Science to
see a simple table that lists the species of Proboscidea that have lived
on Earth. Animals are listed here by era. What species of Proboscidea
still exist today?
Mastodons
Visit this site by the Illinois State Museum to learn more about
American mastodons, Mammut americanum. Mastodons roamed North
America from 3.75 million years ago to just 10,000 years ago. Click
on why to find out why scientists think mastodons became extinct.
