A
fossil
is the remains or trace of an ancient living thing.
[1]
Fossils of
animals
,
plants
, or
protists
occur in
sedimentary rock
.
In a typical fossil, the body form is retained, but the original
molecules
that made up the body have been replaced by some
inorganic
material, such as
calcium carbonate
(CaCO
3
) or
silica
(SiO
2
). The fossil feels like, and is, made of
rock
. It has been
mineralised
or
petrified
(literally, turned into rock).
A fossil may also be an
imprint
or
impression
of a living thing remaining in the fossilised
mud
of a long-gone age.
Some
organisms
fossilise well, others do not. The most common fossils are those left behind by organisms that produce hard materials. The hard,
calcitic
shells of
molluscs
(such as
clams
and
snails
) and of now-rare
brachiopods
(also known as lampshells) are examples. These sea-dwelling
shellfish
have produced many fossiliferous (that is, fossil-bearing)
chalky
layers
of
limestone
in the earth.
Soft-bodied organisms can fossilise in special circumstances: the
Ediacaran biota
is a good example.
[2]
The best-known fossils for the general public are those of the giant,
prehistoric
dinosaurs
. The fossilized
bones
and fossilized
tracks
of these huge,
ancient
reptiles
can be seen in many
museums
of
natural history
and
earth science
.
The study of fossils by
geologists
and
biologists
is known as
paleontology
. If the study puts living things in their
ecological
context it is called
paleobiology
.
Examples of fossils include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants.
People have found many uses for fossils. Some fossils are found and sold. Other fossils like those in the
Tamiami formation
are used in the construction of roads. In some places fossils are used as a mulch- material used to cover soil. Some fossils are used as a marker to determine formation .
Some fossils are used as a source of fuel, these fossils are referred to as a
fossil fuel
.
There are some sites where fossils have been found with remarkable details, or in large numbers. Palaeontologists call these sites by the German term
Lagerstatten
. The
La Brea tar pits
in
Los Angeles
, California, is such a place. So are the
Solnhofen limestone
quarries
in
Bavaria
.
In the Earth’s structure a very important place for fossils is the
Burgess Shale
. It is known for its many important fossil discoveries.
Microscopic
, or
very tiny’', fossils are called “microfossils”. Larger,
macroscopic
fossils ? such as those of
seashells
and
mammals
? are called "macrofossils". Sometimes
natural
stones
look like fossilized
organisms
, but they are not fossils at all. Rather, they are called "pseudofossils".
Although most fossils are formed from the hard parts of organisms, there are also
indirect
signs
of prehistoric life. Examples such as a
worm
's
trail
or an animal's footprint are quite common. These are known as
trace fossils
. Fossilized
excrement
,
faeces
or dung is known as a
coprolite
. A
chemical
trace of prehistoric organisms is called a
chemofossil
. Objects made by prehistoric people are called
artifacts
but these are not fossils.
Even when the remains of soft-bodied animals are gone, there may be impressions, molds or
carbon
traces which remain permanently. So, in special cases, we can see fossils of even small, soft invertebrate animals.
Sometimes a fossil is produced because of dryness (
desiccation
),
freezing
, or
pine
resin
.
Mummified animals
,
ice
-covered wooly
mammoths
, and
insect
-filled
amber
are examples of such fossils.
Living fossils
, however, are
not
fossils at all. Instead, they are modern-day organisms which look like their prehistoric
ancestors
of many millions of years ago. The
ginkgo
tree
, the
coelacanth
and the
horseshoe crab
are good examples.
Many pre-scientific peoples noticed fossils, but not all thought they were the remains of living things. Perhaps the first to leave a record of his thought was the
Ancient Greek
philosopher
Xenophanes
(about 570
BC
?470
BC
).
[3]
p. 387
His ideas were reported by later writers:
- "Shells [are] found in the midst of the land, and on mountains. In the
quarries
of
Syracuse
the impressions of a fish and seaweed have been found; on
Paros
the impression of a bay-leaf in the depth of a stone, and on
Malta
the flattened shape of sea-creatures [have been found]. These, he says, were formed when everything, long ago, was covered in mud, and the impression dried out in the mud". Guthrie p. 387
These ideas were rediscovered in the 17th century in Europe.
Nicolas Steno
in the
Netherlands
and
Robert Hooke
at the
Royal Society
in
London
both wrote and gave lectures about fossils. In the 18th century fossil-collecting began, and serious thinking on
geology
began to make progress. In the 19th century geology became a modern science, and fossils played a part in the theory of
evolution
.
Wikimedia Commons has media related to
Fossils
.
- ↑
Fossil: the remains or impression of a prehistoric plant or animal, usually petrified (turned into stone) while embedded in rock".
Concise Oxford Dictionary
, 9th ed.
- ↑
Levin, Harold. 2006.
The Earth though time
. 8th ed, Wiley N.Y. Chapter 6, p117.
- ↑
Guthrie W.K.C. 1962.
A history of Greek philosophy
. vol 1: The earlier
presocratics
and the
pythagoreans
. Cambridge.
- Iggulden, Hal; Iggulden, Conn (2007). "Fossils".
The Dangerous Book for Boys
. New York: HarperCollins. pp. 19?20.
ISBN
978-0061243585
.
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