Fossils Flashcards
A fossil definition
A fossil is used to describe any trave of past life fossils maybe parts of organisms such as teeth or shells or whole organisms such as body fossils.Fossuls may also be traces of organisms such as footprints or burrows
factors affecting fossilisation
energy levels- low e levels increase chance of fossilisation as high e breaks and erodes deep ocean floor
The transport distance- shorter distance more likely fossilisation is
Rate of burial- fast burial less decay and scavenging so more likely to fossilise
Type of sediment- fine soft sediment= fossilisation more likely
degree of diagenesis- increased temp and pressure means fossilisation less likely
Ph- alkaline= more likely as acid can dissolve the hard parts before they can fossilise
Anerobic conditions- reduces decomp and preserves organisms= fossilisation likely
The presence if hard parts- bones, teeth, shells more likely to survive
The actual comp of the hard parts- some made of Cacium carbonate, Araganite, sillica, chitin and some are harder and less susceptible to acid so easier to fossilise
replacement
The og material is dissolved atom by atom and substituted with another mineral
most common type is replacement of aragonite—> calcite
e.g coral
it can also occur with other minerals present in ground water
silicification
When ground water is rich in sio2
The sio2 is dissolved in groundwater but comes out of solution to fill voids and pores present in og material
if the whole remains have dissolves it can fill the whole void
Carbonation
During diagenisis pressure and temp increases. lots of the volatiles are driven off and all that remains is the carbon, the carbon tends to form thin film fossils
Pyritisation
replacement of the of material by iron pyrites. happens in anaerobic conditiond. sulphur loving bacteria, covet sulphur to bisulphate this reacts with iron= iron pyrite which replaces of material
mould and cast formation
moulds- when fossils dissolve out of rock they are in leaving void, if broken open it would be a mould of fossil, of filled with sediment before complete burial the if broken open an internal mould may be revealed
A cast- formed when void is filled with another mineral, they can bee seen as counterparts to external moulds when rock broken open. Casts can be made in a lab by filling moulds
benothonic and types of benothonic organism
live in the deep sea on the sea floor or sometimes In deep waters
infaunal-live within the sediment
epifaunal- live on the sediment
Vagrant- moves around on the sea floor usually a scavengers/predator
Sessile- an organism that doesn’t move around sea floor they are filte feeders
pelgic and types of pelgic organism
They live In the water column mostly in surface waters top 200m
planktonic- free Floaty go whereever current takes them, filter feeders or photosynthesis
Nektonic- are able to swim/propell they are responsible for own movements usually predators or scavengers
definition of a species
rely on morphology studying the shape, what something looks like. We use morphological similarities to tell species
life and death assemblages
life- if fossils are in their og position this is what we call a life assemblage, more likely to be articulated
death- the remains are found in a diff place to where they would have lived and have been transported. More likely to be disarticulated, mixture of fossils species present
