p. 576 Earth’s Earliest History
The
Divisions of Precambrian Time
Visit this site by the Museum of Paleontology, University of California,
Berkeley to learn more about the Precambrian. There is a nice analogy
here that helps you understand how long humans have existed as compared
to the length of time Earth has existed. At the top of the page is a
timeline showing the divisions of Precambrian time. Click on Archaen
to find out more about life on Earth during the time period from 3.8
to 2.5 billion years ago. What are stromatolites?
The
Age of the Earth
At this United States Geological Survey (USGS) site you can learn
more about the oldest rocks on Earth. Although Earth is between 4.6
and 4.5 billion years old, the oldest rocks have an age of 3.8 to 3.7
billion years. Why haven’t geologists found rocks on Earth that are
as old as Earth itself?
The Earliest Atmospher e, Oceans, and
Continents
Go to this site by the Space Physics Research Laboratory at the University
of Michigan for an explanation of Earth’s early atmosphere, oceans,
and continents. What was the source of present-day oceans? Where did
this material come from originally?
Introduction
to the Cyanobacteria
Visit this Museum of Paleontology, University of California, Berkeley
site to learn more about cyanobacteria. Scientists agree that early
cyanobacteria probably produced oxygen during the Archaen and Proterozoic
eras to form our present-day atmosphere. What is the other great contribution
of cyanobacteria to life on Earth?
p. 588 Ozone in Earth’s Atmosphere
Ozone and the Atmosphere
Go to this National Aeronautics and Space Administration (NASA) site
to learn about the protective role of ozone in Earth’s stratosphere.
Scroll down and click on formation of the ozone layer. What is the origin
of the oxygen in the ozone layer?
Reports to
the Nation on Our Changing Planet: Our Ozone Shield
At this National Oceanic and Atmospheric Administration (NOAA) site
you can find out why the ozone layer is so important to life on Earth,
and how human activities have damaged it. This is a comprehensive look
at what ozone is and how it protects living things from harmful ultraviolet
light. The site also explains how scientists discovered that human activities
were harming the ozone layer. This is an excellent site.
The Ozone Depletion Process
Visit this Environmental Protection Agency (EPA) site to learn more
about ozone depletion in Earth’s atmosphere. This site explains how
chlorofluorocarbons (CFCs) contribute to ozone depletion. Scroll down
and click on ultraviolet (UV) light to see how UV light is affected
by ozone. Which type of UV light is absorbed by ozone?
Basic
Chemistry of Ozone Depletion
At this NASA site you can learn about the basic chemistry of ozone
depletion. Although this site does not have fancy graphics, it gives
you a relatively simple explanation of how ozone is destroyed in Earth’s
atmosphere.
p. 591 Life at Hydrothermal Vents
Ocean
Planet: Recently Revealed
Visit this Smithsonian Institution site for information on life
at hydrothermal vents. The site includes lots of links to additional
information on hydrothermal vents. Scroll down and click on Creatures
of the Thermal Vents to open an article from Popular Science magazine
on this subject. This article nicely sums up what is known about life
at hydrothermal vents. Water pouring out of vents is as hot as 400ºC
and contains hydrogen sulfide. Which of these factors supports life
around hydrothermal vents?
Hydrothermal
Vent Geochemistry
Go to this NOAA site to learn more about the geochemistry of hydrothermal
vents. Hydrothermal systems appear to have a major impact on local ocean
chemistry. What compounds do hydrothermal vents add to seawater?
The
Light at the Bottom of the Ocean
At this site by Science News Online you can find out about
a new discovery at hydrothermal vents deep on the ocean floor—faint,
but detectible, light. Scientists don’t yet understand the source of
this light, but it could be strong enough to allow some photosynthesis
deep in the ocean. This discovery is still being examined.
WHOI
in Motion
Go to this site by Woods Hole Oceanographic Institution to view
images of the organisms found at hydrothermal vents. Click on the slide
at the top left of the screen to see a short movie taken at a vent.
It takes several minutes to load the movie, so be patient. The movie
is very cool.
p. 593 Ediacara Fauna
Edicaran Fauna
Visit this site to read about ediacaran fauna. The article describes a controversy among scientists as to whether the ediacara were ancestral animals. Read the article to form an opinion of your own. Were the ediacara ancestors of today’s animals or were they a completely different form of life?
Learning
About the Vendian Animals
At this site by the Museum of Paleontology, University of California,
Berkeley you can see images of ten edicaran fossils. Click on any image
to see what is known about that fossil. Or you can scroll down and click
on Ediacara Hills to see the location in Australia where these fossils
were first identified. What does the word ediacara mean?
Ediacara
Biota
Go to this site by the Miller Museum of Geology, Queen’s University,
Canada to learn about the ediacaran fossils found in Canada. Since the
discovery of ediacaran fossils in Australia in 1946, such fossils have
been found on every continent except Antarctica. Scroll down to the
map of Canada and click on any of the images to learn more about the
fossils found at that site.
p. 596 Pseudofossils
False
Fossils
At this Geoscience Research Institute site you can read an article
about false fossils. Although this is a scientific article, it shows
how geologic formations can be mistaken for fossils. What is a pisolite?
Concretions
Visit this site to learn about concretions, compact masses of minerals
that at one time were thought to be fossils of plant or animal life.
Read about how concretions form. Why did fossil collectors break open
concretions?
