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WHAT IS A FOSSIL?
Fossils are the remains of prehistoric life or some other direct evidence that such
life existed. The word "fossil" means "dug up", but usually refers to plants or
animals that have become petrified, or "turned to stone". We usually think of fossils
as impressions of ancient life encased in rock, but this explanation is too simple -
not all fossils turn to stone. There are many different types of fossils and processes
of fossilization.
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TYPES OF FOSSILIZATION
Fossils are created in many different ways, under many different conditions. Some
processes are unique and extremely specialized. The most common types of fossilization
are mold and cast fossilization, mineral replacement (petrification), amberization,
mummification, and trace fossilization.
Molds and Casts - Most fossils are formed by the process of mold and cast replacement.
When an animal dies, it becomes buried in the ground, covered by sediment. The remains
of the animal eventually dissolves away so that only a cavity is left behind - a
natural mold. Later, dissolved substances may fill in the cavity, forming a natural
cast of the original animal. This type of fossilization is easily the most common type
of fossilization, found all over the world. There are literally billions of mold and
cast fossils preserved in the Earth's crust.
Mineral Replacement (Petrification) - This takes place when water dissolves the
original hard parts of plants or animals and replaces them with mineral matter. It may
happen so slowly that the new mineral matter duplicates microscopic structures in the
shell, coral, wood, bone, etc. This type of fossilization produces some of the most
complete and detailed fossils ever found. Some petrified wood is so well preserved
that bark patterns, growth rings, and internal cellular structures are all still
intact.
Amberization - Amber, simply put, is ancient tree sap that has turned to stone over
time. Scientifically, amber is the resin of certain trees that has fossilized over
millions of years. It is a light, organic substance that is usually yellow or orange
in color and often transparent. It is formed by trees exuding resin, usually through
breaks or cuts in the bark. Once the resin is expelled, it hardens and drops to the
ground. It is eventually buried in the dirt at the base of the tree and hardens
further. Over the next few thousand years, this resin is called COPAL, which is still
soft and essentially unfossilized. Copal is usually much younger in age than true
amber, and is much less desirable to jewelry makers and collectors. Copal that is
preserved in sandstone will eventially become amber over time - Copal that is preserved
in clay will take much longer to fossilize. This transformation is called
"amberization", and is an ongoing process that takes millions of years. At this point,
this inert resin is considered to be true fossilized amber.
Mummification - Occasionally, plants and animals die under extreme conditions for perfect
preservation - in dry, undisturbed caves or frozen in glaciers, for example. In
these rare circumstances, hair, skin, blood, etc. can be preserved with a minimum of
cellular change. The most well known examples of this type of fossilization are the
frozen Mammoths of Alaska and Siberia. Complete animals have been discovered fully
intact, with internal organs preserved. Mammoth meat is still consumed by the locals
tens of thousands of years after the last Mammoth walked the Earth!
Trace Fossils - Trace fossils are not fossils of actual animals, but fossils of their
"traces". Some examples of trace fossils are footprints, trails, burrows, borings,
coprolites (fossil poop), etc. These are not actual fossil animals, but simply residual
evidence that these animals once existed. Dinosaur tracks are some of the most famous
types of trace fossils.
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FOSSIL TYPES AND LOCALITIES
Many types of plants and animals have been extensively preserved in the fossil record.
The distribution of these fossils encompasses the entire Earth's surface, including
areas on all seven continents. Here are some of the more well known fossil localities
from around the world:
Plants - The Eastern United States and Europe have extensive coal fields where ferns
and related plant fossils are found in abundance. Individual deciduous leaves are
common finds in Colorado and Utah. British Columbia also has a wide variety of fossil
leaves. Large sections of petrified wood are found in Arizona, and Patagonia is famous
for its fossilized pinecones.
Invertebrates - The Burgess Shale locality in British Columbia is probably the most
famous invertebrate fossil site in the world. Trilobites, extinct three-lobed
arthropods, are found in many localities around the world, such as Europe, Australia,
China, Canada, and Utah. Some of the best preserved examples come from Morocco,
Russia, and Oklahoma. Ammonites, related to the modern-day Nautilus, are famous from
Europe and Madagascar, and are also found in Russia, South America, and even the
United States. Insects in amber are commonly found along the Baltic Coastline and the
Dominican Republic. Crinoids are unusual animals related to starfish and sea urchins.
One of the most prolific areas for these fossil "sea lillies" is Crawfordsville,
Indiana, although crinoids have been discovered in China and Australia.
Vertebrates - Dinosaurs are the world's most popular fossil vertebrates, and their
fossils are most commonly found in the Western United States and Canada. Dino remains
are also known from Europe, Africa, Argentina, and China. Aquatic reptiles, such as
Mosasaurs and Plesiosaurs have been found in England, Morocco, Kansas, and Texas.
Mammals, both large and small, are commonly exposed in the Badlands area of South
Dakota and Nebraska. Alaska and Siberia are famous for beautifully preserved Mammoth
fossils, ranging from teeth and tusks to complete animals. Fossil fish are relatively
common in the fossil record. The Green River Formation of Southern Wyoming is world
famous for both its variety of species and its sheer number of specimens. Complete
fossil fish are also known from Europe, Lebanon, Brazil, and China. Shark fossils,
especially teeth, are found all around the world. Some of the more well known fossil
shark localities are the Eastern Seaboard of the United States, Chile, and Morocco.
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FACTOIDS
Crude oil reserves and coal deposits are probably the most abundant fossils on the
planet. These "fossil fuels" are the most consumed energy resources in the world.
Fossiliferous limestones and slates have been used for building stones and roofing
shingles for hundreds of years. Fossils have also been used extensively in jewelry.
Amber and jet, fossilized tree sap and wood repectively, are famous semi-precious
gemstones used in jewelry and trinkets for centuries. Also, many fossil outcrops in
the United States have been converted to National Parks - the Petrified Forest,
Dinosaur National Monument, and Fossil Butte (Fish) National Park are just a few
examples.
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