Fossils And Time Flashcards
What is a fossil?
Describe any trace of past life. May be parts of organisms, or whole body fossils. May be traces such as footprints or burrows
What is a body fossil?
The hard parts of an organism, such as the skeleton or shell
What is dissolution?
The process whereby minerals that make up the fossils are dissolved away and removed away and removed in solution by groundwater
What does articulated mean?
Organisms formed whole or connected, as they are in life
What is the littoral zone?
High-energy area between high and low tide
What is an anoxic environment?
Anaerobic. Conditions lacking oxygen and unsuitable for life
What are resting traces?
A type of trail as the whole body of the animal has stopped moving
What is bioturbation?
Refers to burrowing or working the sediment in a way that disrupts the bedding. This is caused by the activity of living organisms
What is a closure temperature?
The temperature at which a system has cooled, so there is no diffusion of isotopes in or out the system
What are the 9 factors affecting fossilisation?
Presence of hard parts
pH conditions
Energy levels
Rate of burial
Sediment type
Oxygen levels
Transport distance
Composition of hard parts
Amount of diagenesis
How does the presence of hard parts affect fossilisation?
Includes teeth, shells and bones.
More likely to survive diagenesis. Organisms with 100% soft parts are less likely to be fossilised. The fossil record is biased towards organisms with hard parts
How do pH conditions affect fossilisation?
Alkali (high pH) conditions more likely to fossilise. Acidic conditions can dissolve the hard parts before fossilisation
How do energy levels affect fossilisation?
Calm, low energy environments increase the chances of fossilisation.
Higher energy breaks down more
What environment do we get most of our fossils from?
Deep oceans
How does the rate of burial affect fossilisation?
The faster it is buried, the more likely it is to be fossilised. Burial protects it from scavengers and predators
How does the transport distance affect fossilisation?
The shorter the distance, the more likely to fossilise because transport = erosion
How does the sediment type affect fossilisation?
Fine, soft sediment makes fossilisation more likely. Hard, angular rocks more likely to break down rocks
How does the sediment type affect fossilisation?
Fine, soft sediment makes fossilisation more likely. Hard, angular rocks more likely to break down rocks
How do oxygen levels affect fosilisation?
Anaerobic conditions reduce decomposition. More likely to fossilise
How does the composition of hard parts affect fossilisation?
Lots are made of calcium carbonate (CaCO3) which dissolve in acid. May also be made of silica, aragonite or chitin. Some will be harder than others
How does the amount of diagenesis affect fossilisation?
Higher pressure and temperature means it’s less likely to fossilise because they’re more likely to be destroyed
What are the 5 types of fossil preservation?
Replacement
Silicification
Carbonisation
Pyritisation
Mould and cast formation
What is replacement in terms of fossil preservation?
Original material is dissolved and substituted for another mineral. Can occur with other minerals present in groundwater
What is the most common type of replacement (preservation)?
Aragonite –> Calcite
Aragonite is a type of calcium carbonate. Mollusc shells and corals are made of aragonite
What is silicification in terms of fossil preservation?
Occurs when groundwater is rich in silica dioxide (SiO2). The silica dioxide is dissolved in groundwater but comes out of solution to fill voids. If the whole fossil has been dissolved, it can fill the whole void
What is carbonisation in terms of fossil preservation?
During diagenesis, pressure and temperature increases and lots of volatiles are driven off (unstable under new conditions). All that remains is carbon, which tends to form a film fossil (very thin)
What is usually preserved by carbonisation?
Vegetation
What is pyritisation in terms of fossil preservation?
Replacement by iron pyrite. It happens in anaerobic conditions. Sulphur-loving bacteria live in these conditions and convert Sulphur into bisulphates which then react with iron to make iron pyrite (replaces it)
What are moulds and how are they formed?
Formed when fossils are dissolved out of the rock they’re in. This leaves a void in rock. Breaking rock open will reveal external mould of fossil. If fossil filled with sediment before burial may reveal internal mould and structures of fossils
What are casts, and how do they form?
Formed when the void is filled with another mineral, such as iron pyrite or silica. Casts can be made in the lab by filling moulds with latex or modelling clay
What are the two main categories for marine organisms?
Benthonic and Pelagic
What does benthonic mean?
Live in the deep sea usually on the seafloor. Usually, it means it lives in or on the sediment
What categories are benthonic marine organisms split into?
Infaunal, epifaunal, vagrant, sessile
What is an infaunal marine organism?
An organism that lives within the sediment, probably in a burrow
What is an epifaunal marine organism?
An organism that lives on the sediment
What is a vagrant marine organism?
Moves around the sea floor. Usually, they are scavengers or predators
What is a sessile marine organism?
Organisms that don’t move on the sea floor. Some are even attached to a substrate on the seafloor. These are likely to be filter feeders
What are pelagic marine organisms?
Organisms that live in the water column. In the surface water <200m
What are pelagic marine organisms split into?
Planktonic, Nektonic
What is a planktonic marine organism?
Free-flowing organisms. They go wherever the current takes them. Likely to be filter feeders
What is a nektonic marine organism?
Organisms that are able to actively swim. Therefore they tend to be scavengers or predators
What is geomorphology?
Deciding if something is part of a specific species by looking at their similarities (what it looks like, size, shape, etc)
What is a filter feeder?
Organisms that are stationary and wait for food to come to them
What is an assemblage?
A group of fossils found together in a rock
What is a life assemblage?
When fossils are in their original positions and are more likely to be articulated
What is a death assemblage?
The remains are found in a different place to where they formed. More likely to be disarticulated. May be a number of fossils present
What does a thick shell say about an organisms paleo-environment?
Protect themselves in a high-energy environment, such as intertidal beaches. More likely to be preserved
What does a thin shell say about an organisms paleo-environment?
Likely to be found in low energy environments
What does the absence of eyes say about an organisms paleo-environment?
At the time we know eyes formed, this usually lived in areas with no light. Such as the deep sea
What does a compound eye say about an organisms paleo-environment?
Lived in an area that had light. If oceanic, they are pelagic
What are track fossils?
Form when an organism moves on wet sediment, leaving an imprint. The tides cover the tracks with sand, grit, and gravel, protecting them from the effects of sun, wind, and water. The tracks are buried deeper due to sediment accumulation and hardened into rock through lithification. When loose sediments become rock, the footprints within them become fossilised
What are trail fossils?
Impressions of animals which were travelling. This could have formed due to part of all of the animal dragging along the surface of the substrate. For example a trilobite tail. Trail fossils can also be footprints (like track fossils).
What are burrow fossils?
By invertebrate and vertebrate animals mixes and brings rock and soil particles to the surface. This facilitates weathering at greater depth, by providing access for atmospheric gases and water. They are created when animals dig holes or tunnels into the ground or seafloor.
What are borings?
Animal borings in rocks or fossils are formed when organisms, such as marine worms or molluscs, burrow into sediment or hard substrates like wood or shells. These burrows can leave behind distinct patterns or tunnels.
What are excrement fossils?
The waste material of ancient organisms can become preserved in sediment or rock layers. Through this preservation process, the excrement can leave clues about the diet, behaviour and even the environment of the organism that produced it.
What are root structure fossils?
formed through a process called petrification. When plants or trees die and their remains are buried in sediment, minerals in the surrounding water can replace the original material in the roots, turning them into stone over time.
How are bivalves and brachiopods similar? (5)
Both have two valves (shells)
Both have bilateral symmetry
Both have umbo
Both have teeth and sockets
Both have muscles + muscle scars on shell
How are bivalves and brachiopods different? (3)
Brachiopods have central symmetry, and bivalves have hinge line symmetry.
At rest, bivalves are open. Brachiopods are closed at rest
Linked to this, bivalves have one set of muscles to close, brachiopods have two sets of muscles
What is a key feature cephalopods have involving their shells, and what do they do?
Recognised by their chambered shells.
They can adjust the gas and liquid within these chambers. This allows it to control movement within the water column (depth) and their buoyancy
Where are soft parts housed in cephalopods?
In the final chamber - newest and biggest.
Soft parts include tentacles which are used to swim and catch prey
What cephalopod type is used as an index fossil?
Ammonites. Really common and really successful
What are the chambers in a cephalopod?
Series of empty space within the shell which water and gas can enter and leave
What is the siphuncle in a cephalopod?
The tube which connects chambers and controls gas for buoyancy
What is the protoconch in a cephalopod?
The first chamber which is occupied by the juvenile. This is added to by subsequent chambers as the animal grows
What are the septa in a cephalopod?
Or singular: Septum.
The walls closing off the body chamber as the cephalopod grows
What is the aperture in a cephalopod?
The final chamber where the soft parts live. This is the newest and biggest chamber
When was the earliest known coral recorded?
The cambrian era >500Ma
What are coral polyps?
The soft bodies of a coral - rarely preserved
How might corals be preserved?
They secrete a calcium carbonate skeleton. This may also form limestone
What are the three types of coral we should be aware of?
Rugose (horn coral)
Tabular
Scleractinian (only one still around today)
What is a coralite?
1 skeleton from 1 polyp
What is the columnella in coral fossils?
The central rod which provides support to keep fossil upright
What are the septa in a coral fossil?
Vertical plates radially dividing the skeleton of the coralite
What are tabulae in coral fossils?
Horizontal plates separating the coralite skeleton (like floors in buildings)
What are dissepiments in a coral fossil?
Curved plates connecting the septa to the tabulae
What is the calice in coral fossils?
Circular depressed area (bowl) at the top of the coralite, where polyp would live
What is the epitheca in a coral fossil?
The outer layer of the coralite
What are the growth lines in a coral fossil?
Lines forming with growth?
Sometimes match up with tabulae, and are horizontal
What is a bivalve?
They have two valves.
Hinge symmetry.
Shells are same size and shape.
But the face of the shells aren’t symmetrical.
Rest position is open.
Filter feeders. Sometimes attached by a substrate
What does the siphon do in a bivalve?
They are filter feeders so the siphon draws water, nutrients and food. With a second one to exhale
What is an example of a bivalve attached by a substrate?
Mussels
What is a commissior in bivalves?
Where the two shells meet
What are the cardinal teeth and sockets for in a bivalve?
They’re not real teeth, but they allow the valves to lock in place (allow it to close)
What is the umbo in a bivalve?
The most curved/raised bit of shell
What are adductor muscles in bivalves?
They contract and keep the shell closed
What are ligaments in bivalves?
They hold the shells together
What is the pallial sinus in a bivalve?
Not all bivalves have these. These are evidence of syphons being present
What are trilobites?
They were arthropods with a chitin skeleton. They lived from the start of the Cambrian to the end of the permian era
How are trilobites separated?
They are divided into 3 directions longitudinally and laterally
What symmetry do trilobites have?
Bilateral symmetry
What is the name of the ‘head’ section of a trilobite?
Cephalon
What is the name of the ‘body’ section of a trilobite?
Thorax
What is the name of the ‘tail’ section of a trilobite?
Pygidium
What is the cephalon for in a trilobite?
The head of a trilobite. Made up of a series of fused segments
What is the thorax for in a trilobite?
The body part of a trilobite. Made up of separated articulated segments. It protects and covers the gills and legs
What is the pygidium for in a trilobite?
The tail part of the trilobite. Made of a number of segments fused together
What are the genal spines in a trilobite?
the nerve-filled sensory organs. They detect threat
What is the pleuron in a trilobite?
The lateral part of the thorax
What is the compound eye made of in a trilobite?
Calcite
What are the cheeks for in trilobites?
Fixed and free cheek.
They help with shedding
What are brachiopods?
2 valves (shells) often uneven and vary in sizes. They are filter feeders. They have 3 sets of muscles. They can open and close.
What are pedicles on brachiopods?
Brachiopods often have pedicles. These are fleshy stalks which attach to the ocean floor or rocks (substrate). They are filter feeders
What symmetry do brachiopods have?
Bilateral symmetry across the shell face
What is an umbo in a brachiopod?
The area marking the point of first growth
What is the commissure in a brachiopod?
Where the valves meet
What is the one Eon we study?
Phanerozoic Eon
Ranges from the cambrian to the quarternary
What are the three Eras we study? (oldest first)
Paleozoic, Mesozoic, Cenozoic
What are the twelve Periods we study? (oldest first)
Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Palaeogene, Neogene, Quarternary
What are the five mass extinction events? (oldest first)
Ordovician-silurian
Late devonian extinction
Permian-triassic extinction
Triassic-jurassic extinction
Cretaceous-paleogene
When was the Ordovician-Silurian extinction event?
440 Million years ago
When was the Late devonian extinction event?
365 Million years ago
When was the permian-triassic extinction event?
250 Million years ago
When was the Triassic-jurassic extinction event?
210 Million years ago
When was the Cretaceous-paleogene extinction event?
65 Million years ago
When was the Palaeozoic era?
From the cambrian to the end permian.
541-252 million years ago
When was the Mesozoic era?
From the triassic to the cretaceous period.
252-66 million years ago
When was the Cenozoic era?
From the Paleogene to the quarternary.
66-0 million years ago
When was the cambrian?
541-485 million years ago
When was the ordovician?
485-444 million years ago
When was the silurian?
444-419 million years ago
When was the devonian?
419-359 million years ago
When was the carboniferous?
359-299 million years ago
When was the permian?
299-252 million years ago
When was the triassic?
252-201 million years ago
When was the jurassic?
201-145 million years ago
When was the cretaceous?
145-66 million years ago
When was the palaeogene?
66-23 million years ago
When was the neogene?
23-2.6 million years ago
When was the quarternary?
2.6-0 million years ago
What is relative dating?
Putting rocks or events in order by age relatively (so x comes before y)
How can we relatively date rocks using fossils?
Using index fossils. Fossils help if we know the period they lived for. E.g. trilobites are older than ammonites
How can we relatively date using sedimentary structures?
By determining ‘way up’ we can decide whether one bed of rock is older than another bed
How can we relatively date using igneous intrusions?
Intrusions cut across existing rocks
What is the problem with relatively dating?
It doesn’t give us an exact date or time.
What is absolute dating?
Provides us with the actual dates of rocks. Measured in Ma
What is an isotope?
An atom of the same element with a different atomic mass due to a difference in neutrons
How do we use isotopes to absolutely date?
Using their half lives. Some isotopes are radioactive and unstable
What is half life?
The time taken for 50% of the parent isotope to decay into the stable daughter isotope
Why can we not use carbon to absolute date rocks?
It only has a half life of a few thousand years. In geological time, this is too short
How can we use Uranium-238 to absolutely date rock?
Daughter isotope = Lead-206
It is found in zircon.
Has a half life of 4500Ma.
Used to date igneous rocks over 10Ma
How can we use Uranium-235 to absolutely date rock?
Daughter isotope = Lead-207.
Found in uranite.
Half life of 700Ma.
Used to date metamorphic rock over 10Ma
How can we use Potassium-40 to absolutely date rock?
Daughter isotope = Argon-40
Found in both micas and hornblende
Half life of 1280Ma
Used to date metamorphic and igneous rocks over 10,000 years old
How can we use Rubidium-87 to absolutely date rock?
Daughter isotope = Strontium-87
Found in both micas and orthoclase feldspar
Half life 49000Ma
Used to date the oldest rocks
What are the x and y axis in a half life graph?
X-axis - Half life number
Y-axis - Parent isotope %
What mnemonic is used to remember for the geological periods?
Can Our Silly Dogs Carry Perfect Toys Just Carefully Past New Quarters
What mnemonic is used for mass extinction events?
Ordinary Dinos Preffered The Chickens
