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A-Level Geology (1st Year) > Fossils And Time > Flashcards

Fossils And Time Flashcards

1
Q

What is a fossil?

A

Describe any trace of past life. May be parts of organisms, or whole body fossils. May be traces such as footprints or burrows

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2
Q

What is a body fossil?

A

The hard parts of an organism, such as the skeleton or shell

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3
Q

What is dissolution?

A

The process whereby minerals that make up the fossils are dissolved away and removed away and removed in solution by groundwater

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4
Q

What does articulated mean?

A

Organisms formed whole or connected, as they are in life

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5
Q

What is the littoral zone?

A

High-energy area between high and low tide

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6
Q

What is an anoxic environment?

A

Anaerobic. Conditions lacking oxygen and unsuitable for life

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7
Q

What are resting traces?

A

A type of trail as the whole body of the animal has stopped moving

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8
Q

What is bioturbation?

A

Refers to burrowing or working the sediment in a way that disrupts the bedding. This is caused by the activity of living organisms

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9
Q

What is a closure temperature?

A

The temperature at which a system has cooled, so there is no diffusion of isotopes in or out the system

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10
Q

What are the 9 factors affecting fossilisation?

A

Presence of hard parts
pH conditions
Energy levels
Rate of burial
Sediment type
Oxygen levels
Transport distance
Composition of hard parts
Amount of diagenesis

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11
Q

How does the presence of hard parts affect fossilisation?

A

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

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12
Q

How do pH conditions affect fossilisation?

A

Alkali (high pH) conditions more likely to fossilise. Acidic conditions can dissolve the hard parts before fossilisation

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13
Q

How do energy levels affect fossilisation?

A

Calm, low energy environments increase the chances of fossilisation.
Higher energy breaks down more

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14
Q

What environment do we get most of our fossils from?

A

Deep oceans

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15
Q

How does the rate of burial affect fossilisation?

A

The faster it is buried, the more likely it is to be fossilised. Burial protects it from scavengers and predators

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16
Q

How does the transport distance affect fossilisation?

A

The shorter the distance, the more likely to fossilise because transport = erosion

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17
Q

How does the sediment type affect fossilisation?

A

Fine, soft sediment makes fossilisation more likely. Hard, angular rocks more likely to break down rocks

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18
Q

How does the sediment type affect fossilisation?

A

Fine, soft sediment makes fossilisation more likely. Hard, angular rocks more likely to break down rocks

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19
Q

How do oxygen levels affect fosilisation?

A

Anaerobic conditions reduce decomposition. More likely to fossilise

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20
Q

How does the composition of hard parts affect fossilisation?

A

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

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21
Q

How does the amount of diagenesis affect fossilisation?

A

Higher pressure and temperature means it’s less likely to fossilise because they’re more likely to be destroyed

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22
Q

What are the 5 types of fossil preservation?

A

Replacement
Silicification
Carbonisation
Pyritisation
Mould and cast formation

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23
Q

What is replacement in terms of fossil preservation?

A

Original material is dissolved and substituted for another mineral. Can occur with other minerals present in groundwater

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24
Q

What is the most common type of replacement (preservation)?

A

Aragonite –> Calcite
Aragonite is a type of calcium carbonate. Mollusc shells and corals are made of aragonite

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25
Q

What is silicification in terms of fossil preservation?

A

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

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26
Q

What is carbonisation in terms of fossil preservation?

A

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)

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27
Q

What is usually preserved by carbonisation?

A

Vegetation

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28
Q

What is pyritisation in terms of fossil preservation?

A

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)

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29
Q

What are moulds and how are they formed?

A

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

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30
Q

What are casts, and how do they form?

A

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

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31
Q

What are the two main categories for marine organisms?

A

Benthonic and Pelagic

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32
Q

What does benthonic mean?

A

Live in the deep sea usually on the seafloor. Usually, it means it lives in or on the sediment

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33
Q

What categories are benthonic marine organisms split into?

A

Infaunal, epifaunal, vagrant, sessile

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34
Q

What is an infaunal marine organism?

A

An organism that lives within the sediment, probably in a burrow

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35
Q

What is an epifaunal marine organism?

A

An organism that lives on the sediment

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36
Q

What is a vagrant marine organism?

A

Moves around the sea floor. Usually, they are scavengers or predators

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37
Q

What is a sessile marine organism?

A

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

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38
Q

What are pelagic marine organisms?

A

Organisms that live in the water column. In the surface water <200m

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39
Q

What are pelagic marine organisms split into?

A

Planktonic, Nektonic

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40
Q

What is a planktonic marine organism?

A

Free-flowing organisms. They go wherever the current takes them. Likely to be filter feeders

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41
Q

What is a nektonic marine organism?

A

Organisms that are able to actively swim. Therefore they tend to be scavengers or predators

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42
Q

What is geomorphology?

A

Deciding if something is part of a specific species by looking at their similarities (what it looks like, size, shape, etc)

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43
Q

What is a filter feeder?

A

Organisms that are stationary and wait for food to come to them

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44
Q

What is an assemblage?

A

A group of fossils found together in a rock

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45
Q

What is a life assemblage?

A

When fossils are in their original positions and are more likely to be articulated

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46
Q

What is a death assemblage?

A

The remains are found in a different place to where they formed. More likely to be disarticulated. May be a number of fossils present

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47
Q

What does a thick shell say about an organisms paleo-environment?

A

Protect themselves in a high-energy environment, such as intertidal beaches. More likely to be preserved

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48
Q

What does a thin shell say about an organisms paleo-environment?

A

Likely to be found in low energy environments

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49
Q

What does the absence of eyes say about an organisms paleo-environment?

A

At the time we know eyes formed, this usually lived in areas with no light. Such as the deep sea

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50
Q

What does a compound eye say about an organisms paleo-environment?

A

Lived in an area that had light. If oceanic, they are pelagic

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51
Q

What are track fossils?

A

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

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52
Q

What are trail fossils?

A

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).

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53
Q

What are burrow fossils?

A

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.

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54
Q

What are borings?

A

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.

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55
Q

What are excrement fossils?

A

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.

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56
Q

What are root structure fossils?

A

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.

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57
Q

How are bivalves and brachiopods similar? (5)

A

Both have two valves (shells)
Both have bilateral symmetry
Both have umbo
Both have teeth and sockets
Both have muscles + muscle scars on shell

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58
Q

How are bivalves and brachiopods different? (3)

A

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

59
Q

What is a key feature cephalopods have involving their shells, and what do they do?

A

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

60
Q

Where are soft parts housed in cephalopods?

A

In the final chamber - newest and biggest.
Soft parts include tentacles which are used to swim and catch prey

61
Q

What cephalopod type is used as an index fossil?

A

Ammonites. Really common and really successful

62
Q

What are the chambers in a cephalopod?

A

Series of empty space within the shell which water and gas can enter and leave

63
Q

What is the siphuncle in a cephalopod?

A

The tube which connects chambers and controls gas for buoyancy

64
Q

What is the protoconch in a cephalopod?

A

The first chamber which is occupied by the juvenile. This is added to by subsequent chambers as the animal grows

65
Q

What are the septa in a cephalopod?

A

Or singular: Septum.
The walls closing off the body chamber as the cephalopod grows

66
Q

What is the aperture in a cephalopod?

A

The final chamber where the soft parts live. This is the newest and biggest chamber

67
Q

When was the earliest known coral recorded?

A

The cambrian era >500Ma

68
Q

What are coral polyps?

A

The soft bodies of a coral - rarely preserved

69
Q

How might corals be preserved?

A

They secrete a calcium carbonate skeleton. This may also form limestone

70
Q

What are the three types of coral we should be aware of?

A

Rugose (horn coral)
Tabular
Scleractinian (only one still around today)

71
Q

What is a coralite?

A

1 skeleton from 1 polyp

72
Q

What is the columnella in coral fossils?

A

The central rod which provides support to keep fossil upright

73
Q

What are the septa in a coral fossil?

A

Vertical plates radially dividing the skeleton of the coralite

74
Q

What are tabulae in coral fossils?

A

Horizontal plates separating the coralite skeleton (like floors in buildings)

75
Q

What are dissepiments in a coral fossil?

A

Curved plates connecting the septa to the tabulae

76
Q

What is the calice in coral fossils?

A

Circular depressed area (bowl) at the top of the coralite, where polyp would live

77
Q

What is the epitheca in a coral fossil?

A

The outer layer of the coralite

78
Q

What are the growth lines in a coral fossil?

A

Lines forming with growth?
Sometimes match up with tabulae, and are horizontal

79
Q

What is a bivalve?

A

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

80
Q

What does the siphon do in a bivalve?

A

They are filter feeders so the siphon draws water, nutrients and food. With a second one to exhale

81
Q

What is an example of a bivalve attached by a substrate?

A

Mussels

82
Q

What is a commissior in bivalves?

A

Where the two shells meet

83
Q

What are the cardinal teeth and sockets for in a bivalve?

A

They’re not real teeth, but they allow the valves to lock in place (allow it to close)

84
Q

What is the umbo in a bivalve?

A

The most curved/raised bit of shell

85
Q

What are adductor muscles in bivalves?

A

They contract and keep the shell closed

86
Q

What are ligaments in bivalves?

A

They hold the shells together

87
Q

What is the pallial sinus in a bivalve?

A

Not all bivalves have these. These are evidence of syphons being present

88
Q

What are trilobites?

A

They were arthropods with a chitin skeleton. They lived from the start of the Cambrian to the end of the permian era

89
Q

How are trilobites separated?

A

They are divided into 3 directions longitudinally and laterally

90
Q

What symmetry do trilobites have?

A

Bilateral symmetry

91
Q

What is the name of the ‘head’ section of a trilobite?

A

Cephalon

92
Q

What is the name of the ‘body’ section of a trilobite?

A

Thorax

93
Q

What is the name of the ‘tail’ section of a trilobite?

A

Pygidium

94
Q

What is the cephalon for in a trilobite?

A

The head of a trilobite. Made up of a series of fused segments

95
Q

What is the thorax for in a trilobite?

A

The body part of a trilobite. Made up of separated articulated segments. It protects and covers the gills and legs

96
Q

What is the pygidium for in a trilobite?

A

The tail part of the trilobite. Made of a number of segments fused together

97
Q

What are the genal spines in a trilobite?

A

the nerve-filled sensory organs. They detect threat

98
Q

What is the pleuron in a trilobite?

A

The lateral part of the thorax

99
Q

What is the compound eye made of in a trilobite?

A

Calcite

100
Q

What are the cheeks for in trilobites?

A

Fixed and free cheek.
They help with shedding

101
Q

What are brachiopods?

A

2 valves (shells) often uneven and vary in sizes. They are filter feeders. They have 3 sets of muscles. They can open and close.

102
Q

What are pedicles on brachiopods?

A

Brachiopods often have pedicles. These are fleshy stalks which attach to the ocean floor or rocks (substrate). They are filter feeders

103
Q

What symmetry do brachiopods have?

A

Bilateral symmetry across the shell face

104
Q

What is an umbo in a brachiopod?

A

The area marking the point of first growth

105
Q

What is the commissure in a brachiopod?

A

Where the valves meet

106
Q

What is the one Eon we study?

A

Phanerozoic Eon
Ranges from the cambrian to the quarternary

107
Q

What are the three Eras we study? (oldest first)

A

Paleozoic, Mesozoic, Cenozoic

108
Q

What are the twelve Periods we study? (oldest first)

A

Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Palaeogene, Neogene, Quarternary

109
Q

What are the five mass extinction events? (oldest first)

A

Ordovician-silurian
Late devonian extinction
Permian-triassic extinction
Triassic-jurassic extinction
Cretaceous-paleogene

110
Q

When was the Ordovician-Silurian extinction event?

A

440 Million years ago

111
Q

When was the Late devonian extinction event?

A

365 Million years ago

112
Q

When was the permian-triassic extinction event?

A

250 Million years ago

113
Q

When was the Triassic-jurassic extinction event?

A

210 Million years ago

114
Q

When was the Cretaceous-paleogene extinction event?

A

65 Million years ago

115
Q

When was the Palaeozoic era?

A

From the cambrian to the end permian.
541-252 million years ago

116
Q

When was the Mesozoic era?

A

From the triassic to the cretaceous period.
252-66 million years ago

117
Q

When was the Cenozoic era?

A

From the Paleogene to the quarternary.
66-0 million years ago

118
Q

When was the cambrian?

A

541-485 million years ago

119
Q

When was the ordovician?

A

485-444 million years ago

120
Q

When was the silurian?

A

444-419 million years ago

121
Q

When was the devonian?

A

419-359 million years ago

122
Q

When was the carboniferous?

A

359-299 million years ago

123
Q

When was the permian?

A

299-252 million years ago

124
Q

When was the triassic?

A

252-201 million years ago

125
Q

When was the jurassic?

A

201-145 million years ago

126
Q

When was the cretaceous?

A

145-66 million years ago

127
Q

When was the palaeogene?

A

66-23 million years ago

128
Q

When was the neogene?

A

23-2.6 million years ago

129
Q

When was the quarternary?

A

2.6-0 million years ago

130
Q

What is relative dating?

A

Putting rocks or events in order by age relatively (so x comes before y)

131
Q

How can we relatively date rocks using fossils?

A

Using index fossils. Fossils help if we know the period they lived for. E.g. trilobites are older than ammonites

132
Q

How can we relatively date using sedimentary structures?

A

By determining ‘way up’ we can decide whether one bed of rock is older than another bed

133
Q

How can we relatively date using igneous intrusions?

A

Intrusions cut across existing rocks

134
Q

What is the problem with relatively dating?

A

It doesn’t give us an exact date or time.

135
Q

What is absolute dating?

A

Provides us with the actual dates of rocks. Measured in Ma

136
Q

What is an isotope?

A

An atom of the same element with a different atomic mass due to a difference in neutrons

137
Q

How do we use isotopes to absolutely date?

A

Using their half lives. Some isotopes are radioactive and unstable

138
Q

What is half life?

A

The time taken for 50% of the parent isotope to decay into the stable daughter isotope

139
Q

Why can we not use carbon to absolute date rocks?

A

It only has a half life of a few thousand years. In geological time, this is too short

140
Q

How can we use Uranium-238 to absolutely date rock?

A

Daughter isotope = Lead-206
It is found in zircon.
Has a half life of 4500Ma.
Used to date igneous rocks over 10Ma

141
Q

How can we use Uranium-235 to absolutely date rock?

A

Daughter isotope = Lead-207.
Found in uranite.
Half life of 700Ma.
Used to date metamorphic rock over 10Ma

142
Q

How can we use Potassium-40 to absolutely date rock?

A

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

143
Q

How can we use Rubidium-87 to absolutely date rock?

A

Daughter isotope = Strontium-87
Found in both micas and orthoclase feldspar
Half life 49000Ma
Used to date the oldest rocks

144
Q

What are the x and y axis in a half life graph?

A

X-axis - Half life number
Y-axis - Parent isotope %

A-Level Geology (1st Year) (11 decks)

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