What are Fossils
The word fossil literally means “dug up”
Fossils consist of prints or preserved remains of living
Such a definition includes our prehistoric human ancestry and
the ice age fauna such as mammoths for example; as well as
more ancient fossil groups such as the dinosaurs, ammonites
How do fossils form?
Fossilisation requires the following conditions, rapid and
permanent burial which protects the specimen from
environmental or biological disturbance including oxygen
deprivation which limits the extent of decay and also
biological activity such as scavenging; continued sediment
accumulation as opposed to an eroding surface - ensuring the
organism remains buried in the long-term; and the absence of
excessive heating or compression which might otherwise
Water plays a crucial role in fossilisation as it is almost always
involved in the process, even fossils found on land such as
those of dinosaurs, were ultimately preserved in sediments
deposited beneath water for example in wetlands, lakes,
rivers, estuaries or swept out to sea.
The fossilisation process will be further discussed, through the
use of an example of how a fish ends up being a fossil.
A fish that has just spawned dies and sinks to
the ocean floor.
After sometime the fish begins to decay and
is covered with a layer of sediment, rapidly
entombing the fish.
This may be caused by a landslide or earth
quakes experienced at the bottom of the
Once entombed, bacteria eat away that the
decomposing flesh, leaving behind only the
Over time the skeleton is gradually buried
deeper. Slowly the weight of the sediment
compacts, pressing the grains together,
driving excess water out, and depositing
minerals in the pores, and ultimately turning
the soft sediment to hard rock - a process
known as lithification.
As this process takes place, minerals contained
within the sediment replace the original
minerals in the skeleton and fill any voids
formed as parts of the skeleton dissolve. This
process of mineral replacement is known as
permineralisation and results in a
remineralised copy of the original skeleton.
Millions of years may pass and the rock
remains buried deep within the bedrock;
however the collision between
neighbouring continental plates buckle
and uplift the bedrock, raising it above sea
level and exposing it to erosion. Slowly,
rock is stripped away, until eventually the
top of the fish's skull is visible at the
If lucky palaeontologist may stumble
upon the remains of the fish in its
fossilised form, the extraction process is
painstakingly slow, and a generous
amount of rock is retained around the
fossil as to protect the specimen.
An example of what the palaeontologist may find when searching
Mold (imprint) fossils: When a leaf, feather, bone or even a body of an
organism leaves an imprint on sediment, which
hardens and becomes rock
Types of fossils
Cast fossils: When minerals fill in the
hollows of an animal track, a
mollusk shell, or another part of
Fossil fuels: Fuels formed by the remains of dead plants and animals,
such as oil, coal or gas for example
Actual remains: The body of an organism,
with all the parts intact.
Usually preserved in ice,
amber, or tar.
The fifth and final form of fossil is.
Petrified wood: When minerals replace wood or stone
to create either petrified wood or a