Fossils Flashcards
Where are fossils most commonly found?
In sedimentary rocks
When are sedimentary rocks found?
When clay and sand particles are carried from one place to another by water and wind
What are examples of sedimentary rocks?
Shale
Sandstone
Limestone
What are other places that fossils can be found?
Amber Tar pits Ice Volcanic lava Anaerobic swamps
What is amber?
Tree resin that has hardened
What is fossilisation?
The set of inorganic processes by which dead organisms or their parts are transformed into fossils
What are the ideal conditions for fossilisation to occur?
Organism should be covered immediately after death
Harder tissues are better suited to fossilisation
Underwater conditions assist in fossilisation as well
Why should the organism be buried right after death?
It creates anaerobic conditions
This prevents decay
Preserves the organism
Give examples of harder tissues which are often fossilised
Bone Shell Exoskeleton Hair Teeth Woody stems
Why is soft tissue rarely preserved?
It is easier to decay
When can soft tissues be preserved?
Insects in amber (even the hairs on the legs remained) In ice (skin and muscles remained intact)
What are the ten steps of fossilisation?
Death of organism
Rapidly covered by sediment
Soft tissues decay
Hard body parts are hardened or replaced by minerals
More sediment covers it
The sediment is cemented and compressed in layers
Sediment solidifies and forms sedimentary rocks
Fossils remain encased in rock for millions of years
They are pushed up due to the movement of the earth
They are exposed to the surface by the erosion of rock layers or human mining
They are then discovered and carefully removed by palaeontologists
What is petrification?
The process by which organic material, is replaced by minerals
Why is a river or ocean a good place for fossils to form?
Not as many aerobic bacteria (less O2), so less decay
Moving water covers the animal with sediment very quickly
How are fossils dug up?
Through a painstaking process
What are the five types of fossils?
Body fossil Mould fossil Cast fossil Trace fossil Resin fossil
What is a body fossil?
The preserved remains of an organism
What are the two types of body fossils?
Complete
Partial
Which type of body fossil is more common?
Partial
Where are complete organism body fossils normally found?
Ice
Tar
Anaerobic swamps
What are complete body fossils?
Even the soft tissue such as skin and muscle
What is an example of a partial body fossil?
The shells of ammonites
What is permineralistion?
The process whereby the pores of an organism are filled with minerals that petrify it
What is a resin fossil?
A fossil that is preserved in amber
What is a mould fossil?
The imprint of an organism that is preserved in rock
How are mould fossils made?
The hard parts of an organism are trapped in sediment
It then decomposes, but leaves an imprint
What is a cast fossil?
A mould fossil that has been filled with minerals
What are trace fossils?
Signs or marks of organisms that were once living
How are trace fossils made?
An imprint that hardens and is filled with sand or clay
What are examples of trace fossils?
Footprints
Burrows
How many species are present in the fossil records?
An estimated 1/10 000
Why are only 1 in 10 000 species in fossil records?
Most land animals do not die in sediment and are therefore decomposed
Fossils are not formed because of unfavourable conditions
Many organisms consist only of soft tissue and so never fossilise
What kinds of organisms are most commonly fossilised?
Aquatic organisms
