Life and Death Flashcards
What is a fossil
Naturally preserved remains/traces of animals/plants
Is actually quite rare but reasonable ampunt has been preserved
In what environment are you most likely to find fossils?
Low energy environments eg deep ocean, lake eg not mountain stream
Sedimentary rocks
3 ways to increase chances of fossilization
- Burial soon after death
- Environmental conditions with little exposure to O2, light and minimal bacterial decay
- Organism made of geoliogicall stable materilas
Sub 0 temps and low O2 also sometimes allow fossilization of soft bodied animals
Trace fossils vs Body fossils
Trace fossils are the REMAINS OF ACTIVITY, so anything made/produces by the animal: burrow, footprints, poop…
Body fossils are fossilized PARTS OF THE ORGANISM: teeth, leaves, bark, bone…
Mold vs cast
Mold: An imprint has been made into the sediment/rock and this imprint has been preserved
Cast: Stencil/mould has been filled up so the shape of the original organism is recreated and has been preserved
Lagerstätten
Rocks containing both soft and hard bodied animals
Impressions in carbon
Organism squashed by layers of sediment/rock so after its decay, all thats left is a thin layer of carbon imprints because the rest of the organis materila has decayed,
- Precambrian
4600 - 540 million years ago
Mostly simple organisms, disc shaped, but since they didnt have shells, preservation potential small
- Paleozoic
540 - 250 million years ago
Animals with shells
3.Mesozoic
250 - 66 million years ago
Evolution of reptiles/ complex forms of life
- Cenozoic
66 million years ago - present
Mammals
Earths early atmosphere
Composed of water, carbon dioxide, carbon monoxide, methane, nitrogen and sulphur
Building blocks of life
Stromatolites
Earliest fossils (though a bit controversial)
Stromatolites are rocks with a very fine layering of carbonate made by cyanobacteria (excreted O2) trapping and binding sediment particles.
Evidence of bacterial life 3500 million years ago
Presence of light isotope of carbon in minerals in rocks dated from 3500 million years ago
C12 is preferred by living organisms (>C13, C14) eg during photosynthesis, so presence of C12 is evdience for bacterila photosynthesis
The Great Oxidation Event
3500 - 2000 million years ago
(Precambrian)
1) Oxygen produced by cyanobacteria reacts with dissolved iron in water to produce iron oxide –> banded iron formations
2) around 2400 million years ago, tipping point is reached where oxygen is no longer just reacting with iron to produce iron oxide in oceans, it is gathering in the atmosphere–> concentrations remained low until about 580 million years ago, allowign complex life to develop
Ediacran fauna
(Precambrian)
-Disc shaped organisms with radial ridges
-Preserved as impressions (no shells, because no such thing as predators yet)
-Produce cholesterol so animal rather than plant
The Cambrain Explosion
-replace ediacran fauna –> much more diverse
-complex body parts (eyes, brain, shell, skeleton…)
Lagerstätten
Rocks that contain fossils of plants and animals that are rarely preserved, usually because they are soft bodied
What is the Burgess Shale
is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years old, it is one of the earliest fossil beds containing soft-part imprints.
How have the soft bodied animals in the Burgess Shale been preserved?
-Oxygen poor sea floor preventing bacterial decay and scavenging
-flattened and preserved as thin films of carbon
Why did the animals in the Burgess Shale develop spines and armored scales?
Some animals were predators (as can be seen in fossil remains in which gut and last meal have been preserved), so animals needed to evolve strategies to avoid being eaten
Significance of the Burgess Shale
Some animals in the burgess shale are unlike any others in the paleozoic era and even the modern day. Burgess shale almost like an evolutionary experiment–> animals experimenting with the types of forms they can take on and only the best adapted niches continued to develop
Conondont (Cambrian- mid triassic)
-Micro fossil
-Eel like predator
Brachiopod (Paleozoic- Cenozoic)
-particularly abundant prior to Permian/Great Dying)
-Mode of life: filter feeding–> water comes in, goes through LOPHOPHORE (feeding FILTER) where nutrients are absorbed and rest is shot out of organism. PEDICLE (stalk like structure) allows brachiopod to attach itself to rocks, corals and seafloor
Plane of symmetry: cuts through two shells rather than between shells
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Crinoids (Paleozoic- Cenozoic)
-comprised of arms (filter feeding) and stalk.
-commonly found in limestone
-Stalk made of calcite discs with central hole (like polo candy)
Stalk ossicles/discs:
Carboniferous –> like polo mints
Jurassic –> more star shaped
Graptolite (Paleozoic)
- Looks like pencil marking on rock
- Saw-like shape
- Form large colonies and every “tooth” is an organism
Colonial tabulate corals vs solitary rugose corals (Paleozoic)
Tabulate corals: Honeycomb morphology
-Polyp occupied each corralite
Rugose corals:
Ice cream cones
Why the change in number of growth lines in rugose corals during Paleozoic era?
Each line is a DAY of growth
Regular variations in the size and spacing of growth lines reflects lunar, seasonal and annual cycles. The number of growth lines/year can be measured
Trilobites (Paleozoic)
Anatomy and Morphology
- Cephalon (head): some with eyes on either side, some without
- Thorax (body): divided into many pleurae (segments) that enabled them to roll up
- Pygdium (butt/tail end): looks segemented but not flexible like thorax
Name comes from the three lobes (perpendicular to the cephalon, thorax and pygdium)
Trilobites (Paleozoic)
Defense mechnisms
Exoskeleton made of hard calcite making them hard to chew well rolled up into a ball
Some developed curvy/extravagent spines
Trilobites (Paleozoic)
Mode of life
-Float
-Swim
-Crawled or burrowed in the soft sea floor, leaving trace fossils
Trilobites (Paleozoic)
Morphology/ functioning of eyes/ lenses
2 Eyes made up of thousands of individual calcite lenses
-Eyes on stalks because crawled just below the sediment surface
-Those in deep ocean were blind
-eyes curving downwards –> ability to see straight ahead and below, probably a predator to see whats swimming below
Trilobites (Paleozoic)
Exoskeleton
The exoskeleton as well as the eyes moulted
-Temporarily blind creature
+abundant fossils because of exoskeleton fossils
Rhynie Chert (Devonian/Paleozoic)
Lagerstatten from 410 million years ago, Scotland
Appearance of first vascular plants (plants with vessels to transport water and nutrients)
Rhynie Chert (Devonian/Paleozoic):
Permineralisation
All the cells have been infilled with silica/plant matter replaced at the cellular level by silica
Rhynie Chert (Devonian/Paleozoic):
How have they been preserved
Plants and insects lived near a hot spring, so very soon after death, organisms inundated by silica rich hot water and fossilised
Fossilisation so rapid that eve most delicate features preserved
Fossil Grove (Carboniferous/ Mesozoic)
Scotland, while it was near the equator (tropical climate)
Lepidodendron (tree-like plants) have been preserved in sedimnet filled casts, its like an internal mould of the plant
Fossil Grove (Carboniferous/ Mesozoic): environment and impact on Earths atmosphere
Lepidodendron grew in a subtropical setting like a swamp forest.
The plant reamins in the swamp is what accumulated to make large coal deposits to fuel industrial revolution
Burial of plant material removed a lot of CO2 from the atmosphere + Plant growth adds O2 to atmosphere = Carboniferous atmosphere had 35% O2 (current day has 21%) which allowed insects to grow huge
Solnhofen limestone (Jurassic/Mesozoic)
Lagerstatten from 150 million years ago, Germany
Development of birds
Bones and impressions left are very detailed because deposited in very fine grained limestone
Solnhofen limestone (Jurassic/Mesozoic):
Depositional environment and preservation
Depositional environement: lagoons near shallow tropical sea
+not much current to disturb remains at bottom
+Bottom fairly stagnant, salt and anoxic, good for preservation
+ toxic floor environment means predators and scavengers absent
Solnhofen limestone (Jurassic/Mesozoic):
Archaeopteryx
Has beak, feathers, claws, teeth and solid bones: bird or dino?
“Dino-bird” that evolved from small carnivorous dinosaurs
Could probably fly/glide short distances
Solnhofen limestone (Jurassic/Mesozoic):
Archaeopteryx relevance
The first skeeton was found 2 years after Darwin published “The Origin of Species” thus supporting his ideas
Close relative of the true ancestor of birds
Ammonites (Jurassic- Cretaceous)
Looking like an underwater snail x squid
Ammonites (Jurassic- Cretaceous): Shells, fossilisation and mode of life
Siphuncle penetrates all septa and connects all chambers. It allows water or gas to pass in chambers allowing pressure to be regulated–> gives ammonite ability to move
Shells are made of aragonite, which is often not preserved. Most fossils are molds, or casts made from sediment or minerals (e.g., pyrite).
Ammonites (Jurassic- Cretaceous): morphology
Shell is divided into chambers by septa, with animal living in outermost chamber
Ammonites (Jurassic- Cretaceous): Suture lines
Ammonite species can be distinguished is from their ‘sutures’ - curved or intricate lines on the outer surface of the shell. Sutures occur where septa meet the shell surface
Bryozoans
Ordovician - present
Mode of life:
Immobile, cemented to sea floor
Sclereactinian Corals
Triassic - present
Aragonite skeleton
Bivalves (Cambrian - present)
Two shells made of calcite and /or aragonite
Filter feeders
Living at lowest levels if body of water (benthic) within or on sediment
Line of symmetry is between two shells, two valves of bivalve are usually mirror images of each other
Foraminifera
Cambrian - present
Microfossils
Good indicators of temperature and salinity
Single celled with shell made of calcite, aragonite or silica
Planktonic or benthic
Radiolarians
Cambrian- present
Microfossils
Single celled with mineralized skeleotn of silica
Planktonic aka floating in ocean
Relative vs absolute stratigraphy
Relative: eg you see rocks and can say that the oldest is at the bottom so the upper layer is younger relative to the bottom
Absolute: measuring exact age by dating rocks
Biostratigraphy
uses fossils to correlate rocks and determine their relative age
Biozone
The upper and lower limits of a rock based on the presence and/or abundancethe of one or more species of fossils
Zone fossils are used to define biozones
Characteristics of a good zone fossil
+Worldwide geographical distribution
+Evolves quickly, so any one species has a short lifespan
+abundant
+easy to identify (through patterns, specific characteristic)
+Readily fossilised
Good zone fossils
AMMONITE
Swam in the oceans so are found on many different types of marine rock
Easy to recognize because of suture patterns
Types of Biozone
Total Biozone:
organisms first appearance - extinction
Acme Biozone:
biozone defined by where this organism is especially abundant
Partial Range Biozone:
Like total biozone but you’re taking into account the appearance/ disappearance of other species to define the biozone
Assemblage Biozone:
Biozone is the area where a variety of organisms are living at the same time
Types of Biozone
Total Biozone:
organisms first appearance - extinction
Acme Biozone:
biozone defined by where this organism is especially abundant
Partial Range Biozone:
Like total biozone but you’re taking into account the appearance/ disappearance of other species to define the biozone
Assemblage Biozone:
Biozone is the area where a variety of organisms are living at the same time
A biozone may not represent the same time interval everywhere that it occurs, because:
-A species may not have appeared and gone extinct at exactly the same time everywhere
-A species may originate in a small area, then some time later expand
-A species may go extinct in most areas, but hang on in one place
-The lack of fossils of a given species may just be because it has not been preserved, or just not yet been found
- End Ordovician 443 million years ago
(Mass Extinction)
Extinct species:
80% of all species, mainly marine invertebrates
Causes:
1) Global Cooling –> Burial of animals removes CO2 from atmosphere.Glaciation and lowering of sea levels affect warm shallow animals mostly
2) Global Warming–> Melting of glaciers
- Late Devonian 370 million years ago
(Mass Extinction)
Extinct species:
75% of marine species
Causes:
Land surface colonised by plants, greater rates of rock weathering, CO2 levels drop
GLOBAL COOLING, glaciation in Southern hemisphere
- Great Dying/ Permian 251 million years ago
(Mass Extinction)
Boundary between Paleozoic and Mesozoic
Extinct species:
96% of marine animals including trilobites
70% of terrestrial animals
Causes:
Volcanism –> rise in CO2 levels –> global warming –> acidification and stagnation on sea floors
+ammonia and methane in atmosphere
4.End Triassic 201 million years ago
(Mass Extinction)
Extinct species:
80% of marine species including conondonts and loss of mammals that allow diversification of dinosaurs to take up left over niches
Causes:
Intense volcanic activity leading to greenhouse warming and ocean acidifcation
5.Cretaceous- Paleogene 66 million years ago
(Mass Extinction)
Extinct species:
75% of species, allowing mammals and birds to diversify/ take over the niches
Causes:
Asteroid impact
Cretaceous- Paleogene 66 million years ago
(Mass Extinction): Evidence
All around the world, a thin layer can be found that contains a chemical element that is more rare to Earths crust and more common in meteorites
Consists of:
-an ejecta layer: containing glass droplets thrown out by the impact
-fireball layer that contians mineral grains that have experienced high pressure eg diamonds
180km crater found buried beneath limestone in Mexico
Cretaceous- Paleogene 66 million years ago
(Mass Extinction): Effect on global climate
Immediate effects:
-Sunlight blocked by rock dust and soot (from wildfires) ejected into the atmosphere. A ‘nuclear winter’.
-Photosynthesis fails
-Global cooling to sub zero temps for many years
Long term effects:
-Global warming due to the burning of vegetation releasing CO2 and CaCO3 vaporizing
Cretaceous- Paleogene 66 million years ago
(Mass Extinction): Implications
Would mammals have evolved if this asteroid hadn’t hit? Because the took over the niches the dinosaurs etc left behind and evolved and diversified
