What are Fossils?
Fossils are the prehistoric remains of a plant or animal.
Fossils are typically preserved when they are buried under many layers of sand
and mud. Under great pressure the sand and mud become sedimentary rock. Minerals
seep into the fossil replacing the organic matter and creating a replica in
stone.
  A
fossil can be a trace fossil or a body fossil. A body fossil is what was actual
organic material from a creature or plant (like a bone). Trace fossils are signs
of plant and animal activity that have been preserved in rock. For example,
dinosaur tracks, trails and dung are all trace fossils.
A body fossil is usually composed of the bones of an animal.
Preservation of the "soft" tissue of a body is rare especially over long periods
of time. Most body fossils are made when an animal dies and falls, or is washed
into a stream, and is covered with mud.
In a few cases, though, fossils have been preserved by freezing
( as with mammoths in Siberia
and Alaska) or when the animals have become mired in a tar pit (such as the
famous La Brea tar pit near Los Angeles, California).
Sometime a fossil is the result of a volcanic eruption. Ash and
mud from the volcano can cover animals and plants killing and preserving them at
the same time.
Fossils come in all sizes. The largest are
dinosaur bones (which may be
ten or more feet in length for a single bone) and the smallest are plant spores
only a few hundredths of an inch across. The study of fossils is called
Paleontology. The study of fossil plants is Paleobotany.
Fossils exist all over the world. As hills erode, fossils become
visible and a Paleontologist can find and remove them for study. Sometimes a
small area only a few hundred feet across will be jammed with skeletal remains.
This is called a "bone bed." A bone bed maybe the site of a sandbar on an
ancient river. During floods, the bodies of many animals floated downsteam,
grounded on the bar, and quickly got covered with silt and were preserved.
Removal of fossils from the rock is done very carefully to avoid
damage to the specimen. Photographs are taken to record the position of the
bones as they were found. These aid scientists as they attempt to reconstruct
fossil skeletons.
Fossils are laid down in the rock layers in order of age. The
oldest fossils are deeper and the new fossils farther up in another "strata" of
rock. Geologic action, though, jumbles this over a wide area so that fossils
from the Cretaceous Era (65 million years ago) might be on the surface only a
few miles from fossils of the Ice Age (10,000 years ago). A Paleontologist knows
where to go to find the right age rock for the type of fossils he is seeking.
The petrified lump of dinosaur
dung shown below is a "trace" fossil.
Here are some examples of other types of fossils:
 PLANT REMAINS
Hard seeds and woody structures are more commonly found than
flowers and leaves. The flowers and leaves themselves are not preserved,
but the carbon impression of them can leave most of the detail showing
their delicate structure.
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 ANIMAL REMAINS
Teeth, bones and shells are much more commonly
found than the rarer skin, flesh, fur, and hair and feather
parts. Usually only 1 or 2 bones and or teeth are found at a
time and you can count yourself extremely lucky if you come
across or unearth a whole skeleton.
There has been the odd rare occasion when an entire mammoth has been discovered in places such as Alaska or Siberia, frozen solid for millions of years. These ‘frozen fossils’ have preserved not only the bones and teeth but the entire animal.
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MOLLUSKS
Just like today when you can pick up sea shells along the
sea shore, during prehistoric times the shells of sea
animals also collected along the banks plains and coastline,
when the sea retreated the shells became covered in mud,
silt and sands and can be found today throughout many
geological periods. |
 AMBER
(Fossil Tree Resin) - Amber is fossil tree resin (tree sap),
sometimes fossil insects can be found trapped in the amber.
Amber is highly sought after and is usually made into
jewelry.
There are a number of locations along the UK
coast where amber is found, Southwold is one of the most
popular locations in East Anglia.Amber is orange, yellow,
green or red. |
COAL, GAS, OIL
More commonly known as 'Fossil Fuels'. The burning of fossil
fuel is said to be speeding up climate change by increasing
levels of Carbon Dioxide (Co2) in the atmosphere causing
heat to become trapped causing 'The Greenhouse effect'.
Coal is actually dead fossil plants and animals
carbonized and compressed over time which is why it is so highly flammable. Oil is also the remains of animals and plants but was formed during marine environments. Gas was formed from rotting vegetation. |
 MOULDS AND CASTS
(trace fossils) - Often fossils found are not the original
plant or animal material, but the mould or cast of it.
During fossilization the original material sometimes
dissolves away leaving a cavity, which, over time fills in
with other dissolved substances. This type of fossil is
known as a mould. Casts are another type of fossil found.
Casts are hollowed impressions of the original fossil or
mould. Types of casts that can be found are the foot prints
and animal trails. |
 RIPPLE MARKS AND MUD CRACKS
Occasionally, rocks that were formed in shallow seas, lakes
or rivers have been left with ancient ripple marks on them
caused when the soft mud dried. Mud cracks were formed in a
similar way, when the soft wet mud dried out quickly.Ripple marks and mud – cracks can tell us much about the
climate and environment when they were formed. For instance,
we know there must have been water, sun and warm
temperatures at the time they were made. |
 COPROLITES
Coprolites are the fossilized excrement of ancient animals. |
 FOOTPRINTS (trace fossils)
Fossilized footprints of dinosaurs and mammals can be found.
The photo shows a dinosaur footprint at Hastings, UK. These
are formed in certain conditions such as mud when the
dinosaur walked over muddy land, over time sediments laid on
top and the footprints can be found today. |
 BORINGS (trace fossils)
Borings are small channels
and tunnels made by worms and mollusks that lived millions
of years ago; these can sometimes be found in fossil wood
and shells. |
Portions of the above information are Copyright Lee Krystek, 1996.
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