Eviden ce of Ev o lu tio n
Fossils
How are they formed
Fossilisation happens rarely, when a plant or animal dies in the right conditions
To become a fossil - die in a location where the skeleton is protected from scavengers
and natural elements.
eg: Burried in sand, soil or mud
Best place: seabed or riverbed
Sediments (sand/mud) become compressed when on its way to becoming a rock
Chemicals and minerals trickle through sediment & original bone or shell gradually
recrystallises.
In extreme cases the entire skeleton can dissolve away, leaving a hollow
In other cases, Minerals from rocks gradually soak the bone, shell or wood - changing
its chemical composition + making it capable of surviving for as long as the rock
enclosing it.
In cases the original has dissolved away, minerals fill the hollow to create a natural cast
Sometimes a fossil doesn’t contain anything of original creature except shape.
Rocks also have a finite lifespan. Rock enclosing fossil can be eroded away, fossil is
revealed on surface of ground.
If luck it’ll be excavated but if not elements will batter it until reduced to sand or
mud.
Main types of Fossils
Body Fossils Bones, Teeth, Shells
Formed when hard parts of animals = trapped under layers of sediment
and turn into rock
Most common type of fossil
Moulds & Casts Forms when hard parts of organism = buried in sediment
Hard parts = completely dissolved over time
Leaving hollow area with organisms shape.
Cast forms as a result of a mold.
Water + Dissolved minerals + Sediment = fills molds empty spaces
Minerals + Sediment - left in mold = makes a cast
Cast = Opposite of mold
, Trace Fossils Show activities of organisms
eg: Footprint
Overtime, footprint = buried in layers of sediment
Sediment becomes solid rock.
Preserved Fossils Fossils that are completely preserved in natural preservative
eg: Ice, Resin, Lava
Microfossils Fossils of organisms that need to be viewed under microscope
Famous Fossils
Otzi the Iceman A naturally mummified fossil
Found between Austria and Italy
Believed to have been murdered due to an arrow head found in his
shoulder.
Body was covered in ice shortly after his death - which is why there is
so little deterioration.
Preserved in ice - with his clothes and weapons
Preserved fossils like this = very valuable
as there is a lot of info = extracted
Berezovka Mammoth Well preserved “wooly mammoth”
Found in Siberia on banks of Berezovka River
Mammoth was flash frozen, buried in frozen mud
with preserved food still in its mouth
Only head and neck exposed
Died suddenly due to landslide of frozen mud
Petrified Forest in Arizona American national park in Arizona
named after abundance of petrified wood
Trees date back to 225 mya (mill years ago)
During floods, water forced trees to be pulled up from
ground and were permineralized
Volcanic eruptions nearby entombed some of the trees
Fossils
How are they formed
Fossilisation happens rarely, when a plant or animal dies in the right conditions
To become a fossil - die in a location where the skeleton is protected from scavengers
and natural elements.
eg: Burried in sand, soil or mud
Best place: seabed or riverbed
Sediments (sand/mud) become compressed when on its way to becoming a rock
Chemicals and minerals trickle through sediment & original bone or shell gradually
recrystallises.
In extreme cases the entire skeleton can dissolve away, leaving a hollow
In other cases, Minerals from rocks gradually soak the bone, shell or wood - changing
its chemical composition + making it capable of surviving for as long as the rock
enclosing it.
In cases the original has dissolved away, minerals fill the hollow to create a natural cast
Sometimes a fossil doesn’t contain anything of original creature except shape.
Rocks also have a finite lifespan. Rock enclosing fossil can be eroded away, fossil is
revealed on surface of ground.
If luck it’ll be excavated but if not elements will batter it until reduced to sand or
mud.
Main types of Fossils
Body Fossils Bones, Teeth, Shells
Formed when hard parts of animals = trapped under layers of sediment
and turn into rock
Most common type of fossil
Moulds & Casts Forms when hard parts of organism = buried in sediment
Hard parts = completely dissolved over time
Leaving hollow area with organisms shape.
Cast forms as a result of a mold.
Water + Dissolved minerals + Sediment = fills molds empty spaces
Minerals + Sediment - left in mold = makes a cast
Cast = Opposite of mold
, Trace Fossils Show activities of organisms
eg: Footprint
Overtime, footprint = buried in layers of sediment
Sediment becomes solid rock.
Preserved Fossils Fossils that are completely preserved in natural preservative
eg: Ice, Resin, Lava
Microfossils Fossils of organisms that need to be viewed under microscope
Famous Fossils
Otzi the Iceman A naturally mummified fossil
Found between Austria and Italy
Believed to have been murdered due to an arrow head found in his
shoulder.
Body was covered in ice shortly after his death - which is why there is
so little deterioration.
Preserved in ice - with his clothes and weapons
Preserved fossils like this = very valuable
as there is a lot of info = extracted
Berezovka Mammoth Well preserved “wooly mammoth”
Found in Siberia on banks of Berezovka River
Mammoth was flash frozen, buried in frozen mud
with preserved food still in its mouth
Only head and neck exposed
Died suddenly due to landslide of frozen mud
Petrified Forest in Arizona American national park in Arizona
named after abundance of petrified wood
Trees date back to 225 mya (mill years ago)
During floods, water forced trees to be pulled up from
ground and were permineralized
Volcanic eruptions nearby entombed some of the trees
