B. Origins and Extinctions Flashcards
1
Q
What does the first fossil evidence we have imply?
A
It is already fairly complex, implying that much of early history of life is missing from the geological record.
2
Q
How long did life remain at the microbial level (what fraction of geological time)?
A
7/8
3
Q
How old is the Universe based on astronomical observations?
A
12-14 billion years old
4
Q
When did Earth and the Solar System form?
A
4.5-4.6billion years ago from a spinning nebula of gas and dust
5
Q
Describe the Big Bang event and why the Big Bang is relevant.
A
Big Bang event = the Universe expanded from a primodrial hot dense initial condition; expansion and cooling contrinues until today.
Relevant since all the matter that would eventually form the Sun, planets, and life ultimately trace their origins to the “Big Bang”
6
Q
The earliest fossils that have been discovered to date are those of fairly advanced microbes. This means one of two things: (which are…?)
A
- Life was brought to Earth from outer space at that particular time and at that specific stage of development. However, this is unlikely as the fossils we find appear to have been very well adapted to conditions on Earth, something that would have taken time.
or…
2Life arose on Earth but as we are missing much of the early history of life on our planet there is no evidence of this found to date. Much of this record has probably been removed by tectonic activity and erosion.
7
Q
Describe early life forms on Earth.
A
They were anaerobic (lived in environment with no free oxygen) and heterotrophic (do not synthesize their own food but ingest it from surrounding environment)
8
Q
Define prokaryote
A
an organism that lacks a cell nucleus or any great complexity of internal cell structure
9
Q
What is ATP?
A
adenosine triphosphate, an organic compound that gives energy to cells
10
Q
What are autotrophs?
A
Autotrophs are organisms that produce complex organic compounds from simple inorganic compounds and energy.
11
Q
Describe fermentation
A
the simplest autotrophic process that organisms could use
12
Q
Describe how the earliest life developed
A
Earliest life form probably anaerobic, probably heterotrophic.
Overall, a microbe that was a prokaryote, lived in early oceans, fed on organic compounds produced from inorganic constituents.
Eventually ATP supply in ocean would deplete so competition for it led to evolution of new strategies of nutrition and metabolism, like those by autotrophic bacteria. The next strategy probably the simplest is fermentation. (Photosynthesis more complicated so developed later)
13
Q
Describe the earliest fossil evidence.
A
The earliest fossil evidence is found in the Australian Apex Chert. Although somewhat controversial, these fossils are dated at 3.5 billion years and resemble modern day cyanobacteria, which are photosynthetic in nature.
There is the hint of photosynthesis at an earlier date in the Isua Formation in Greenland. Even though no fossils have been found there, the rocks at this location are enriched in isotopically light carbon isotopes (carbon-12), a signature of photosynthesis. Although an interesting possibility, this finding remains controversial; some have claimed that the isotopic signatures could be the result of later contamination.
14
Q
Describe stromatolites and how they form.
A
They are sedimentary structures formed when mats of cyanobacteria (blue-green algae) develop in shallow-water marine conditions. Over time, these mats then trap and bind the sedimentary (inorganic) grains. Cyanobacteria are photosynthetic, so they must then move up through the sediment and form another cyanobacterial mat on top in order to continue having good access to the sun. The process then repeats, so that over time, layers of sediment accumulate and are later preserved as rocks through diagenesis.
15
Q
How old are the oldest stromatolites discovered? Where were they found?
A
located in western Australia; these have been dated to be about 3.5 billion years old
16
Q
What was different about life in Archean vs. today for stromatolite structures?
A
During the Archean, stromatolites started to get larger and more complex. This change probably reflects the growth of the continents through this time period, which increased the area covered by shallow marine conditions where stromatolites flourish. Life in the Archean was also entirely microbial so stromatolites grew unharvested. Today, more complex (and larger) life forms continuously graze on stromatolite domes. This prevents stromatolites from growing unchecked.
17
Q
What are eukaryotes?
A
All life forms that are not some form of bacteria. They can be distinguished from prokaryotes in that they are larger and possess complex internal cell structures called organelles. These are responsible for various functions within the cell. In addition, DNA is contained within a distinct nucleus rather than distributed through the cell cytoplasm as it is in prokaryotes.
18
Q
Aside from eukaryotes, what other innovation was vital for increased diversification of life?
A
Sexual distinction.
Most prokaryotes (though not exclusively) reproduce by binary fission, where identical copies of the parent cells are produced. Sexual reproduction increases diversity much more efficiently by increasing the variation in offspring. Sexual reproduction increased the tempo of evolution.
19
Q
What are some of the oldest eukaryotic fossils found?
A
Some of the earliest potential fossil evidence we have of potential eukaryotes has been dated to be around 900 million years old. Found in the Bitter Springs Formation in Australia.
More recent studies suggest the oldest eukaryotic fossils may be between 1.8 - 1.4 Ga years old. The biological affinities of these fossils are uncertain, although they are believed to be acritarchs, some kind of spherical, organic-walled algal protists.
20
Q
What are Banded Iron Formations?
A
21
Q
When was the Great Oxygen Crisis? What was it?
A
The transition from a world with little to no oxygen to one that is oxygen-rich. We can say with some confidence that this occurred between 2.5 to 1.8 Ga (billion years ago)
22
Q
What was the source of the oxygen that changed Earth’s environment
A
Cyanobacteria. They produce oxygen as a byproduct of photosynthesis
23
Q
Why are stromatolites called “extremophiles”?
A
They live in extreme enviroments
24
Q
How do scientists remove possible contamination from the core samples pulled from the Earth?
A
Clear tje pitsode pf tje cpre and grind to fine powder
25
What mineral makes the rock beds in Australia red?
mineral hemotide, iron oxide, rust
26
How did this mineral accumulate on the sea floor?
Dissolved iron from ocean combined with oxygen and precipitated out as iron oxide and settled to sea floor and accumulated.
27
What is the source of this oxygen?
Living organisms excreting oxygen
28
Why are stromatolites dome shaped and not flat?
to get nearer to sunlight
29
Advantages to being a multicellular organism?
1. One can get larger and interact more effectively with the environment.
2. One has the possibility of living longer by replacing dead cells.
30
What are Ediacaran fossils?
The frist undisputed metazoans. The earliest large body fossils are the Ediacaran fossils, 570-543 million years old.
31
Describe rangiomorphs
A type of Ediacaran fauna, "spindle creatures" with a simple fractal body plan, lay on the ocean floor
32
Describe the Avalon Explosion
first time animals getting composite body plan instead of being simple sponges;
thin osmotrophs mostly fixed to ocean floor in darkness
33
What are Ediacarans
Perhaps proto animals,
or failed evolutionary experiments in the metazoans (before plants and Cambrian)
34
What period is the Ediacaran
Last period of the Precambrian
35
Describe the Avalon assemblage vs Ediacaran assemblage vs the Nama assemblage;
Temporal relationships of the assemblages?
Avalon assemblage was the stuff found in Newfoundland;
Ediacaran assemblage (in Australia): shallow sandy, within photic zone, temperate cnditions, arid to cool/temperate climate; fossils preserved when covered by storm sands;
Nama Assemblage: tropical distribution found mostly in Namibia, sandbars at front of delta distributaries;
The Avalon-type at the first pulse, rangeomorphs
Second wave of Ediacaran and Nama types, still has rangeomorphs but also other types
36
Innovations in the Ediacaran?
tri and radially arranged organisms (not widely accepted as them being ancestral to echinoderms);
interacting with Earth system, sensing, head and tail and gut and symmetries, biomineralization
by terminal Ediacaran: bioturbation= increased levels of ecosstem engineering, burrowing underneath microbial mats
37
Describe the Ediacaran fauna
organisms that were essentially soft-bodied with no internal skeletons or external shells
Dickinsonia: resemble a large segmented worm, earliest evidence of animals moving in biosphere (ocean floors were encrusted with microbial mats, and trace fossils show them absorbing the microbes on a mat)
They existed in Ediacaran "second wave"
Spriggina: Segments specialized perhaps into functional areas. May have had a head and a tail; similar areas on Parvancorina; both suggested as possible ancestors of arthropods
Kimberella: slug-like creature, interact with sediment via raking for microbes, biosphere is no longer passively interacting with Earth system, is bilaterally symmetrical
Ikaraia: small (grain sized), associated with trails and burrows (can sense), move like and Earthworm, probably fed on buried organic matter, probably had a mouth, anus, gut
Cloudina: evidence some creatures had started to biomineralize (secreted a calcite external skeleton)
38
What happened to majority of Ediacaran fauna?
Some fauna have been found in the Cambrian, i.e. they made it through; most extinct by Early Cambrian
Changing conditions of preservation: many Ediacarans found were preserved by microbial mantling
Increased predation: eat Ediacarans (who were mostly immobile and not skeletized)
39
Where and how did Fractofusus live?
How many genetic commands did it take for these animals to construct their bodies?
How common is Fractofusus in the Mistaken Point Assemblage?
How did Fractofusus grow?
Bottom of ocean
6-8 genetic commands (25k needed for mammals)
Fractofusus is the most common fossil in the Mistaken Point assemblage
It lay o nthe sea bottom, consists of elements (20 each side) and grow in a fractal pattern (each branch the same as its predecessor)
40
Define metazoans
multicellular, eukaryotic organisms
41
What evidence do we have of earlier metazoans existing?
Traces of larger creatures that were moving around in ocean sediments have been found and dated that are older than Ediacaran fossils.
Fossils older than the Ediacaran fauna have been recovered from the Ediacaran Doushantuo Formation (635 - 551 million years old) in South China. These extraordinary fossils of animal embryos are preserved in Doushantuo phosphorites and cherts.
42
Describe the Cambrian Explosion
Cambrian Explosion is a burst in innovation in creatures with hard parts
It is during this relatively short period of geological time that all the major body plans will develop and ultimately evolve into the diverse creatures we are familiar with and see on Earth today. Put another way - all the diversity we see in higher life at present will come from tinkering with the basic body plans developed in the Cambrian Explosion.
43
Hypothesis for how creatures first developed hard parts?
There is an interesting hypothesis that attempts to explain how hard parts first developed in these metazoans. It has been suggested that external shells might have developed as the by-product of evolving metabolic processes. The hypothesis proposes that as metazoans got larger they had to develop more efficient strategies for removing waste products generated by metabolic processes. This generally involved the evolution of ducts and tubes that would collect waste and move it outside of the organism. Some of the minerals in these waste products would then precipitate on the animal's external surface.
44
Over time, creatures that started to secrete this hard external mineral coating, and eventually shells and/or skeletons, would have a selective advantage for a number of reasons including:...?
A hard shell would give greater protection from ultraviolet radiation. During the Cambrian, more UV radiation penetrated into shallow water because the ozone layer was thinner.
A hard shell would help prevent desiccation in organisms caught in an inter-tidal environment.
Hard parts can support soft tissues and act as supports for muscles and therefore aid locomotion.
Hard parts protect organisms from predators.
45
How many phases to the Cambrian Explosion?
There are at least 3 phases to the Cambrian Explosion. The two earliest phases include more simple shelled forms and we won't be getting into detail on them for this course.
46
What are trilobites
Some of the most conspicuous and common arthopods of Early Cambrian
47
What other groups developed in Early Cambrian?
Several other groups also developed at this time including the first mollusks (for example, snails and clams), echinoderms (for example, sea stars and sea urchins), and a group of creatures called brachiopods that resemble clams but are not mollusks.
48
What are brachipods?
A group of creatures. resemble clams but are not mollusks
49
Describe the Burgess Shale and its fossil importance.
A Middle Cambrian biosphere.
Creatures with hard parts, such as trilobites (that had an external skeleton) are common by the time the Burgess Shale animals were preserved. Nevertheless, the Burgess Shale is actually a really important fossil find due to the preservation of creatures that lacked significant hard parts! This is because softer-bodied creatures very rarely survive the processes of fossilization, so this type of fossil location is really unusual! The Burgess Shale records a period just following Phase 3 of the Cambrian Explosion. This time would see the emergence of some new forms, but not to the same dramatic degree or rapidity of the Early Cambrian. In effect, life was starting to evolve within the body plan "rules."
The Burgess Shale organisms lived on top of an algal reef in shallow warm waters. Evidence indicates that this part of B.C. (and all the other areas where Burgess Shale fossils have been found) was close to the equator at this time.
50
Describe Pikaia, why is it significant?
Was found in the Burgess Shale.
It is from the chordates that vertebrates and ultimately humans will evolve. Pikaia was only a very minor component of the Burgess Shale fauna.
51
How did plants find a way to move onto land?
Developed plant cuticle, a waxy covering that helps prevent desiccation. Also stops films of water developing on the plant, which would otherwise reduce CO2 uptake from atmosphere. Also may have provided some rigidity
52
Advantages and disadvantages of plants having cuticle?
Good: prevent drying, stop water film development that reduce CO2 uptake, provide structure
Bad: inhibit nutrient absorption, prevent direct diffusion of gases into plant cells
53
How did the plants change according to the disadvantages of the cuticle?
Cuticle inhibits the absorption of nutrients --> roots had to develop to gather nutrients from the soil which could then be passed to the upper parts of the plant.
c=Cuticle would prevent direct diffusion of gases into the plant cells --> necessitating the development of stomata (specialized pores) that allow the passage of CO2 into the plant. The plant requires specialized guard cells that can open and close these stoma to protect the plant from excess water loss during warm conditions. These pores link to an intercellular gas transport system between cells… which solves another problem…. transporting material including food to the roots which, as they are buried, cannot produce it themselves.
Eventually a very efficient piping system, the xylem, would evolve which would improve the flow of water through the plant. Xylem is composed of dead cells placed end on end, forming a long tube along which water moves. Water moves up from the roots as a result of negative pressure developed by water evaporating from the upper surfaces of the plant – a process called transpiration. Any plants with a xylem are termed vascular plants. However, the pressures developed in the xylem by transpiration can be quite extreme and can cause the collapse of the xylem. Probably as a result of this problem, some plants started to develop a strengthening substance called lignin. Lignin allowed plants to start getting larger.
54
What is transpiration?
The evaporation of water from plant leaves
55
What are vascular plants?
Plants that have a xylem & phloem
56
What enables plants to get larger?
Lignin, a strengthening substance; probably developed due to extreme pressure collapsing the xylem during transpiration
57
What is the phloem?
Another transport system in plants. This is a cell to cell transport mechanism that moves the products of photosynthesis (such as sugars) all around the plant – this is particularly important for areas that may need more energy (like growing tips) or the roots that cannot photosynthesize.
(Seems to wrap around the xylem)
58
When did the earliest plants make their way onto land? When did leaves evolve after that? When did vascular plants evolve?
The earliest plants like liverworts and mosses made their way onto land by at least 470 million years ago, during the Ordovician, although leaves did not evolve for another 80 million years after that! It wasn't until about 433 Ma that vascular plants (those with xylem and phloem) had evolved.
59
What was the first land animal? When did it exist?
The first land animal, a millipede is known to have occurred on land in the Late Silurian, about 428 million years ago.
60
When did the first vertebrate emerge onto land?
They first emerged onto land during the Late Devonian, about 365 million years ago.
61
Compared to arthropods, what additional challenges did vertebrates have to overcome?
Land dwelling vertebrates would have to turn "fins into limbs" before they could make the move to land.
62
What kind of fish did land vertebrates likely evolve from?
lobe fin fish like Eusthenopteron via intermediate forms such as Tiktaalik
63
When did amphibian tetrapods evolve?
By the Late Devonian amphibian tetrapods (animals with 4 limbs) like Icthyostega had evolved. It is from animals like these that the vast diversity of land animals would radiate.
64
What morphological changes are required in order for animals to move out of the water and onto land?
trade gills for lungs, new way of breathing, get around on land (limb supports); develop new ways to see, hear, smell
65
What tool do paleontologists have to tell how these creatures moved around?
digital 3D model and ran tests
66
What does the tool in Question 2 suggest about how tetrapods were moving at this time?
either like mudskippers or moved limbs in parallel
67
What is the hypothesis around why 5 digits is the ideal number for animal's moving on land?
Maybe due to pressure placed on small bones of wrist and ankle joints when more than five fingers, but not enough evidence.
68
What was the "Age of Fishes"?
The Devonian period
69
Dollo's Law?
When complex features in body are lost, unlikely to regain because genetic features lost are highly unlikely to reoccur
70
What did Dr. Simon Braddy believe was the cause of the Cambrian Explosion?
71
What broad biological group do we (humans) belong to?
72
What strategies could Pikaia have used to escape predators?
73
What was Pikaia's descendent in the Soom shale? How did this creature "make a living"?
74
Who was the top predator in the Soom shale?
75
What catastrophe occurred 440 million years ago?
76
Which are more likely to survive such an event, generalists or specialists?
generalists
77
What animal group first left the seas and came onto land? What advantage(s) did they have and what important disadvantage?
78
What period's beginning is marked by the end-point of the end of Permian extinction?
end-point of the extinction at the end of the Permian marked the beginning of a new grouping of periods in the Mesozoic
79
What period's beginning is marked by the end-point of the end of Cretaceous extinction?
the end of the Cretaceous extinction is so distinct that it marks the beginning of the latest grouping of periods that make up the Cenozoic
80
What brackets the Mesozoic (non-avian dinosaur time)?
the Mesozoic (non-avian dinosaur time) is bracketed by extinction events
81
What is the most severe extinction event?
The End-Permian (Permian-Triassic or PT) Mass Extinction
82
Describe the PT Mass extinction
Sometimes referred to as "the Mother of all Extinctions", the PT saw the extinction of more than 50% of all families and around 96% of all species on the planet. It was the time that complex life almost died out on planet Earth, and it is the turnover of species in this event that defines the end of the Paleozoic. It is this event that allowed for the evolution of the Mesozoic Biosphere
83
What group would mammals later evolve from?
a very successful and diverse group of reptiles called the synapsids or mammal‐like reptiles
84
Describe the biosphere prior to the PT Extinction? What were the top land predators?
Prior to the PT extinction, Permian rocks contain evidence of a rich biosphere both on land and in the oceans. The Earth possessed extensive healthy reef systems and jungles full of a diverse reptile and amphibian fauna. In the Southern Hemisphere there was a prolific swamp fauna, which formed the coals that are mined extensively today in Australia.
The top predators on land were the Gorgonopsians, some of which reached the size of a large bear. Gorgonopsians were part of a very successful and diverse group of reptiles called the synapsids or mammal‐like reptiles.
85
Describe what happened following the PT extinction event with regards to the Earth environment/ geology.
Following the PT extinction event, there is evidence of profound changes in the style of sedimentary rocks.
In the shallow ocean environment, instead of limestone produced by corals and other reef creatures or sediments showing intense bioturbation, black fine-grained shales containing high concentrations of the mineral pyrite (FeS2 or "Fool's Gold") dominated.
On land, the rocks were often red like a desert landscape with evidence that soil horizons were stripped and washed away to the oceans.
The coal forming environment in the Southern Hemisphere (and the all the plants associated with them) dried up and disappeared.
Instead of the rich and diverse fossil faunas prior to the extinction, marine rocks (if they contained any fossils at all!) are dominated by a few species such as the "paper pecten" Claraia and the inarticulate brachiopod Lingula. These species were often present in very high numbers.
86
What do monospecific assemblages indicate?
They are often indicative of a stressed environment where only very few or just one species have the necessary adaptations to survive stressful conditions. This species then proliferates due to the lack of any other competition.
87
Describe the Lystrosaurus
one of the few remaining synapsid reptiles to survive the PT extinction event and will become one of the most common terrestrial vertebrate of the Early Triassic; very few reptiles or amphibians on land survived, but Lystrosaurus did
88
Describe the PT extinction phases timeline.
The fossil record provides a detailed account of the order of species that became extinct. The extinction appeared to consist of three distinct phases:
Phase 1: The extinction of land plants and animals lasting about 40,000 years.
Phase 2: At about 40,000 - 45,000 years after the start of the event, extinction of oceanic species begins. This event is shorter and sharper than the extinctions on land.
Phase 3: The extinction moves back onto land and continues to remove species until about 80,000 years after the initiation of the event.
89
Describe the geochemical signature associated with the PT extinction
a dramatic shift in oxygen isotope values with a decrease in the 18^O ratio of about 6 parts per thousand (ppt) at the extinction
90
Explain possible causes of the End-Permian (PT) mass Extinction.
1. Change in continental configuration - drop in biodiversity. As discussed earlier, the greater the landmass the greater the competition between species. At the end of the Permian the supercontinent Pangea or "all lands" would have brought many species into direct competition.
2. Sea level fall - less ocean ridge activity. Seafloor spreading slowed its pace during the Permian. As a result, the oceanic ridges were smaller in size and displaced less water. Consequently oceans retreated from shallow areas into the deeper basin causing problems for creatures that lived in any remaining shallow marine environments.
3. Oceanic stagnation. The end of the Permian saw the end of an Ice Age. Previously cold polar waters might have warmed, effectively slowing or stopping ocean circulation. This would have reduced ventilation of deep ocean waters, killing off many deeper marine species. In addition, occasional overturn of stagnant water could have brought oxygen poor waters to shallower marine communities. It has been proposed that there could also have been a release of large clouds of carbon dioxide from these stagnant waters, which would have suffocated many creatures living along the edge of the Panthalassic Ocean.
4. Climate change. Due to the formation of a large landmass, climate would have been much drier and subject to drought.
5. Siberian Traps - massive volcanic activity in Russia. Around 2-3 million km3 of basaltic lava were produced within a million years during the formation of the Siberian Traps. The Siberian Traps erupted about 250 Ma and are the largest known outpourings of lava that cover large areas of the Earth's surface. Carbon dioxide from the volcanic activity would have raised the average global temperatures by greenhouse warming.
A secondary effect would have been the melting of gas hydrates. Gas hydrates are substances that resemble ice but contain a lot of gas. They are found in ocean sediments along continental margins. If warmed, they destabilize and release methane, a gas that is an even more efficient greenhouse gas than carbon dioxide. It has been proposed that the initial warming of the oceans would have been sufficient to melt the gas hydrates, releasing methane and further driving the greenhouse effect and warming of the planet. In addition, gas emission from volcanoes would have also produced acid rain effects and helped destroy the ozone layer.
6. Possible impacts. Although still very controversial, it is possible that the Earth suffered impacts from space during this time as well. No impact crater has been found but in the South African Karoo, there is a very sudden change in the style of sedimentation from that deposited in a slow moving meandering river environment to a system dominated by braided rivers and streams. This kind of transition is common in an environment where there has been a sudden catastrophe like that which occurred following the eruption of Mount Saint Helens (see figure below). It has been suggested that similar depositions would be created following a large impact event.
91
Describe the Buckminster fullerenes or "buckyballs" and why are they significant?
They are particular organic molecules; a cage-like carbon compound consisting of 60 or more carbon atoms.
Found around the Permo-Triassic boundary. Buckyballs have the ability to trap atoms within their structures; it was found that gases in buckyballs from the Permo-Triassic boundaries are similar to those in extra-terrestrial buckyballs. Although the Permo-Triassic impact hypothesis appears to be supported by intriguing evidence from both the Karoo sediments and buckyballs, it still lacks the overwhelming evidence that exists for the Cretaceous-Paleogene impact.
Support the idea of potential extra-terrestrial impact: L. Becker and colleagues discovered these fullerenes at the boundary between the Permian and Triassic periods
92
Describe the End-Cretaceous Mass Extinction
Over 50% of all species on the planet became extinct during the Cretaceous-Paleogene (K/P) extinction event. In general, the extinction was more severe in the oceans where around 80 - 90% of marine species (including the ammonites and marine reptiles) became extinct. On land, few creatures over 25 kg in weight survived. Notable exceptions to this are crocodiles and alligators; these two groups probably survived as a result of their status as generalists in the ecosystem. They are not 'fussy' eaters and can survive for long periods of time on little or no food.
93
NOTE: Until recently, the time interval between the Mesozoic and the Quaternary was known as the Tertiary. The latter interval is now defunct, as it has been formally divided into two different periods, the Paleogene and the Neogene. This means the Tertiary is no longer recognized as a formal Period in the Geological Time Scale. This change means that you can expect to see reference to both the Cretaceous-Paleogene (K/P) boundary in more recent scientific literature and the Cretaceous-Tertiary (K/T) boundary in the older scientific literature. They mean the same thing.
ok
94
What were some things the K/P extinction known for?
Death of terrestrial dinos.
Also a major extra-terrestrial impact event.
95
Why crocs and alligators survive the K/P extinction?
They were generalists, i.e. not picky eaters and could withstand environments
96
Describe the findings of the Alvarez team- what did they suggest?
The Alvarez team was investigating a clay layer that occurs in a geological section that crosses the K/P boundary in Gubbio, Italy. The 1-cm clay layer lies directly on top of the latest Cretaceous rocks and was found to be enriched in the element iridium. Iridium is very rare at the Earth's surface this layer was enriched over 300X above background. This iridium anomaly has now been recorded in many other sections around the world that straddle the Cretaceous/Paleogene boundary.
Iridium is known to exist in higher concentrations in extra-terrestrial objects such as asteroids.
Alvarez suggested that the clay layer enriched in iridium had been produced by a meteor or comet over 10 km in diameter impacting the Earth. He also suggested that this impact may have also been responsible for the extinction at the end of the Cretaceous.
97
Describe the evidence in detail that support an impact in the K/P event. (at the end of the Cretaceous)
1. Iridium anomaly (rare on surface so must be from outer space)
2. Spike in fern spores in sedimentation suggest huge fire before. A fern spike is exactly the scenario that is recorded in earliest Paleogene sediments, suggesting that global forest fires may have raged at the end of the Cretaceous, leaving a landscape open for ferns to spread.
3. Soot- commonly associated with the clay layer that is very high in iridium at the K/P boundary: evidence of massive global fires.
4. Tektites: Many tektikes at K/P boundary at different locations, which suggest massive impact.
5. Shocked quartz: thought to be prdouced when rock is shattered during a high-energy impact; found across the K/P bounary between North and South America.
6. Tsunami Deposits: Found sedimentological evidence of a massive mega tsunami at the K/P boundary in Mexico, Texas, New Jersey, and the Carolinas, many times greater than the one that hit Indonesia in 2004. The size of this tsunami could not be explained by any of the tsunami generating phenomena operating on the Earth (earthquakes, volcanoes and landslides). Something had generated a tsunami so large that it had penetrated deep into continental interiors, deeper than would appear reasonable. Such a wave could have been generated if an impact had occurred in the ocean.
7. Found the Chicxulub Impact Crater in the Yucatan Peninsula
98
What's the relationship between fern spores and fires?
After the fire has passed certain plants are well adapted to colonize a fire devastated landscape. Commonly these plants are species of fern. Ferns release masses of spores into the environment, many of which get incorporated in sediments.
A good way to investigate local forest fire activity is to take a vertical core of sediments from nearby lakes and see where you get an increased abundance of fern spores relative to pollen…. this spore ‘spike’ acting as a proxy for a forest fire. A fern spike is exactly the scenario that is recorded in earliest Paleogene sediments, suggesting that global forest fires may have raged at the end of the Cretaceous, leaving a landscape open for ferns to spread.
99
What are tektites and why are they important?
Tektites are composed of natural glass and are thought to be produced during impact events. During impact, rock is melted and ejected from the crater. As it travels through the air and cools, it forms characteristic aerodynamic shapes. Many tektites are found at the K/P boundary in many different locations, suggesting a massive impact event.
100
What are shocked quartz? Why they important?
Fragments of mineral quartz that have multiple fractures. These fractures are thought to be produced when rock is shattered during a high-energy impact. The fragments are called shocked quartz. The shocked quartz had a particularly high concentration between North and South America across the K/P boundary.
101
Describe the Chicxulub Impact Crater and the object that caused it.
It is a large circular disturbance over 180 km in diameter found in the Yucatan Peninsula of Mexico.
The object responsible for this crater had a shallow angle of entry around 20 - 30° and is estimated to have been at least 10 km across.
(Think of Mt. Everest hitting the Earth)
The energy released by the impact was equivalent to 6.2 x 107 tons of TNT causing about 100 km3 of rock to be vaporized and released to the atmosphere. Material that wasn't instantly vaporized was thrown out of the crater (the ejecta) and was deposited to the northwest of the impact site.
102
Describe the short term effects of the impact that formed the Chicxulub Impact Crater.
Initial effects (seconds to days): If you were close enough to the Yucatan Penninsula you would probably have heard a sonic boom as the impacting body entered the atmosphere and then a detonation! A pulse of intense heat and light would move rapidly out from the impact site, vaporizing all that was close by and causing organic material, plants and animals to spontaneously combust farther away.
The impact itself would have caused the Earth to ring like a bell with seismic energy. A shockwave would move out from the impact site carrying with it superheated rock debris (including tektites) and molten material igniting fires (supported by the soot and subsequent fern and pollen data) and depositing a thick layer of ejecta in Mexico and the southern states.
It would have also generated the largest tsunami probably ever seen in the history of Earth’s Biosphere.
103
What is the 'Tanis'?
An area called 'Tanis' preserves a fantastic record of what happened in the minutes and hours proceeding the impact. This site is the remains of a river system that flowed south into an existing inland sea near the central-east side of the North American craton during the Late Cretaceous. Scientists believe that seismic waves from the impact may have triggered a 'seiche' (giant wave)* that rushed northward from the inland sea and up that river, only about 6 - 13 minutes following the impact. This wave would have thrown up and stranded many fish and marine creatures that were subsequently fossilized in the rock record from the area.
104
How far away is Tanis from the impact site?
more than 2,000 miles away
105
What is the evidence that the fossil fish at Tanis died within an hour of the impact and not due to the other effects that followed later?
"impact spherules" -- small bits of molten rock thrown up from the crater into space where they crystallized into a glass-like material -- were found lodged in the gills of the fish
106
How have some of the original spherules found at the Tanis site survived unaltered after so long?
What two kinds of rock fragments are found within the spherules?
some spherules that landed in tree resin on the surface of a log that fateful day and were preserved in amber; no water could get to them thus never turned to clay or anything
Most of these tiny rock fragments within the spherules were calcium-rich -- likely from the limestone under the Yucatan Peninsula
107
What part of a dinosaur was found at Tanis and what tissue did it have preserved?
Thescelosaurus limb, a leg specifically. The preservation of soft tissue such as skin suggests that its body did not have any time to decay before it was buried in sediment.
The only two supported scenarios here are that it died in the surge or that it died immediately before (the asteroid strike) but so close in time that it really did not have time to decay. This is not something that had died years before and then been reworked. That does not happen with soft tissue like that.
108
What kind of flying reptile egg was found at Tanis and what did it allow us to confirm about the morphology of the egg?
a fossilized pterosaur egg, the first found in North America
It shows that the eggs of the giant flying reptiles were soft like those of many reptiles today.
109
Describe the long term effects of the impact that formed the Chicxulub Impact Crater.
Nuclear winter / Cold House due to fine particles released into atmosphere following the impact, cooling Earth significantly and preventing photosynthesis in both oceans and land.
Once Cold House over, leavesa fine layer of iridium rich clay that marks the end of the Cretaceous, but due to death of plants, food chain severely collapsed. Herbivores starved, and then carnivores.
Once dust fully settles, water vapour remained in atmosphere, acting like a blanket, preventing heat from escaping the Earth. Created a greenhouse effect causing a rise in global temp.
Eventually excess water vapour removed by rainfall but temp rises still from greenhouse gasses ("Hot House") that lasts years to decades. CO2 liberated when large quantities of limestone/ calcium carbonate were vaporized during impact.
Also, acid rain. Affects organisms forming base of food chain/web, so very serious for all creatures at higher trophic levels.
110
What was poisoning the Cretaceous atmosphere?
111
What effect did volcanic gas have on the reproduction of Tyranosaurus rex?
112
What was the early warning of the approaching Chicxulub asteroid that the dinosaurs might have witnessed?
113
Why did Anatotitan have to travel so far to find food?
114
What effect does the changing atmosphere have on Torosaurus herds?
115
Why are creatures with specialist life styles at risk during times of environmental stress?
116
Why does Didelphodon (an early marsupial mammal) have an advantage over specialists?
117
How long ago was the K/P event?
65 million years ago
118
True or False: there were multiple impacts around the time of the K/P event.
True. A group of scientists recently discovered a new crator, the Nadir crator, off the west coast of Guinea and Guinea-Bissau in western Africa. This crator is 8.5km wide, meaning an asteroid of about 400 meters hit the African Coast sometime within a million years of the event in the Yucatan Peninsula.
119
1. How close in age are the Nadir and Chicxulub crators to one another?
2.How far from Chicxulub is the Nadir Crator?
3. What could finding the Nadir crator suggest about Earth's orbit during this time?
4. Is it possible that there could be other undiscovered crators near this age that are yet to be discovered?
1. Within 1 million years of age; the Nadir Crater object could have hit just moments after Chixulub, or hundreds of thousands of years later.
2. 5,500 kilometers away
3. It could suggest that around 66 million years ago, Earth’s orbit carried it into a cluster of asteroids, called an asteroid “family,” and at least two of them scored direct hits. That could mean that for days or weeks, Earth’s skies rained space rocks.
4. Possible yes.
120
What percent of large impact craters have been preserved?
15-25% estimated by geologists
121
What are Deccan Traps?
Formation of Deccan Traps in India, were highly active during that time (similar to Siberian Traps at end of Permian); produced lots of magma and gasses which affeced climate.
122
Why are generalist creatures more likely to survive extinction? What plants were best able to survive?
The creatures most likely to survive all the changes in environmental conditions would have been the generalists who did not require specific foodstuffs or particular environments to thrive.
It would also help if a creature were small enough to be able to hide or burrow away from the more severe environmental changes. On land, the plants that were best able to thrive after the mass extinction event were the angiosperms.
123
Describe the End-Cretaceous Mass Extinction's end
The Late Cretaceous biosphere was probably already stressed. The Chicxulub impact acted as the "final nail in the coffin", taking an already "sick" biosphere further than it might have gone into a mass extinction event.
The creatures most likely to survive all the changes in environmental conditions would have been the generalists who did not require specific foodstuffs or particular environments to thrive. It would also help if a creature were small enough to be able to hide or burrow away from the more severe environmental changes. On land, the plants that were best able to thrive after the mass extinction event were the angiosperms.
124
1. How important is the Amazon to the South American continent?
2. How diverse is the Amazon and what role do angiosperms play in this modern forest?
3. What did the community look like in the Amazon prior to the end-Cretaceous mass extinction?
4. Why did all major plant groups survive the end-Cretaceous mass extinction when many animal groups did not?
5. How did angiosperm diversity increase after the end-Cretaceous mass extinction when compared to the ferns and gymnosperm diversity?
6. What were the causes proposed for the turnover noted in Question 5?
7. What type of canopy forests exist today and what effect did that have on today's Amazon Rainforest?
1. Very. Lots of plants and animals, regulates the entire continent's climate.
2. Important for diversity, allow small trees and shrub to thrive too due to leaves blocking sun
3. Gymnosperms and ferms and lycophytes existed back then there. Angiosperms could not really compete.
4. Animals need lots of food. Plants had spores. Spores prevented extinct.
5. Pre-impact: about 50-50 diversity. Post-impact: 84% angiosperms
6. Most gymnosperms thrive in low nutrient environment (slow growth and water efficient), the impact was like a fertilizer bomb. Also legumes make their own fertilizers. Also: dinosaurs- no more dinos to trample around; angiosperms got enough shade and can flourish
7. Open vs closed. Depending on canopy closed or open, different carbon isotopes (more similar understory and canopy if open). Today Amazon is closed canopy.
