Fossils
What are they?
Fossils are our window into the past.
The word ‘fossil’ comes from the Latin word fossus, which
means ‘dug up’. This refers to the fact that fossils are the
remains of past life preserved in rock, soil or amber.
Generally, the remains were once the hard parts of an organism,
such as bones and shell although, under exceptional
circumstances, soft tissues have also fossilised. There are
different types of fossils because remains can be preserved in a
variety of ways.
How are fossils formed?
Four types of fossils??
Trace Fossils
Trace fossils are the preserved evidence
of an animal’s activity or behaviour,
rather than the remains of the animal
itself. Examples of trace fossils that have
been found include:
● trilobite tracks
● marine invertebrate burrows
● ichthyosaur coprolites (fossilised poo)
Fossils with some organic material preserved
Animal and plant remains can undergo a variety of
physical and chemical changes during
fossilisation.
This results in fossils showing varying styles and
degrees of organic preservation:
● minimal decay with only some loss of soft
tissue
● preservation of a skeleton with minimal
change
● removal of all organic material except carbon,
which remains as a film in the rock
Mineralised Fossils
These fossils are formed when organic matter in remains is
gradually replaced with minerals, ultimately turning the
remains to ‘rock’. Types of replacement include:
● Replacement of organic material in bone with minerals
● Replacement of shell with pyrite
● Replacement of shell with opal
● Replacement of wood with silica – petrified wood
True form fossils
When the animal has been trapped inside a fast cooling liquid
DATING - no not that kind ...
So, how do we know how old a fossil is?
There are two main methods determining a fossils age, relative
dating and absolute dating.
Relative dating is used to determine a fossils approximate age
by comparing it to similar rocks and fossils of known ages.
Absolute dating is used to determine a precise age of a fossil
by using radiometric dating to measure the decay of isotopes,
either within the fossil or more often the rocks associated with it.
Index fossils
Are widely spread around the world / can be found in lots of places.
The rock they exist in has been dated using absolute dating (radiometric) so we
can compare fossils above and below them to get an approximate age.
Dating information and question sheet
https://www.fossilera.com/pages/dating-fossils
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Read the info on the link and answer the following questions