B. Origins and Extinctions Flashcards
What does the first fossil evidence we have imply?
It is already fairly complex, implying that much of early history of life is missing from the geological record.
How long did life remain at the microbial level (what fraction of geological time)?
7/8
How old is the Universe based on astronomical observations?
12-14 billion years old
When did Earth and the Solar System form?
4.5-4.6billion years ago from a spinning nebula of gas and dust
Describe the Big Bang event and why the Big Bang is relevant.
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”
The earliest fossils that have been discovered to date are those of fairly advanced microbes. This means one of two things: (which are…?)
- 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.
Describe early life forms on Earth.
They were anaerobic (lived in environment with no free oxygen) and heterotrophic (do not synthesize their own food but ingest it from surrounding environment)
Define prokaryote
an organism that lacks a cell nucleus or any great complexity of internal cell structure
What is ATP?
adenosine triphosphate, an organic compound that gives energy to cells
What are autotrophs?
Autotrophs are organisms that produce complex organic compounds from simple inorganic compounds and energy.
Describe fermentation
the simplest autotrophic process that organisms could use
Describe how the earliest life developed
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)
Describe the earliest fossil evidence.
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.
Describe stromatolites and how they form.
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.
How old are the oldest stromatolites discovered? Where were they found?
located in western Australia; these have been dated to be about 3.5 billion years old
What was different about life in Archean vs. today for stromatolite structures?
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.
What are eukaryotes?
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.
Aside from eukaryotes, what other innovation was vital for increased diversification of life?
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.
What are some of the oldest eukaryotic fossils found?
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.
What are Banded Iron Formations?
When was the Great Oxygen Crisis? What was it?
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)
What was the source of the oxygen that changed Earth’s environment
Cyanobacteria. They produce oxygen as a byproduct of photosynthesis
Why are stromatolites called “extremophiles”?
They live in extreme enviroments
How do scientists remove possible contamination from the core samples pulled from the Earth?
Clear tje pitsode pf tje cpre and grind to fine powder
What mineral makes the rock beds in Australia red?
mineral hemotide, iron oxide, rust
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.
What is the source of this oxygen?
Living organisms excreting oxygen
Why are stromatolites dome shaped and not flat?
to get nearer to sunlight
Advantages to being a multicellular organism?
- One can get larger and interact more effectively with the environment.
- One has the possibility of living longer by replacing dead cells.
What are Ediacaran fossils?
The frist undisputed metazoans. The earliest large body fossils are the Ediacaran fossils, 570-543 million years old.
Describe rangiomorphs
A type of Ediacaran fauna, “spindle creatures” with a simple fractal body plan, lay on the ocean floor
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
What are Ediacarans
Perhaps proto animals,
or failed evolutionary experiments in the metazoans (before plants and Cambrian)
What period is the Ediacaran
Last period of the Precambrian
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
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
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)
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)
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)
Define metazoans
multicellular, eukaryotic organisms
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.
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.
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.
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.
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.
What are trilobites
Some of the most conspicuous and common arthopods of Early Cambrian
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.
What are brachipods?
A group of creatures. resemble clams but are not mollusks
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.
