History of Life Flashcards
What is the Haldane-Oparin hypothesis?
- hypothesis on how the creation of life came from inorganic origins, via abiotic synthesis of organic monomers
How does the Haldane-Oparin hypothesis propose life began?
- a ‘reducing’ atmosphere of methane, Co2, etc. in combination with higher UV radiation and lighting caused sudden synthesis of amino acids, sugars, lipids, and nucleotides
What is abiogenesis?
origin of life from non-living matter
What is the issue with the Haldane-Oparin hypothesis?
- there is no fossil record of abiogenesis
- can never recreate the exact conditions within a lab
- HOWEVER, there are chemical signatures than represent potential for life to occur
What is the major evidence for pre-cambrian life?
stromatolites, essentially fossil remains of bacteria within sedimentary rocks
What are the challenges in evidencing earliest life?
- while genetic relationships show that life occurred prior to the earliest fossils, we don’t have major evidence prior to the Cambrian as there is a large fossil record gap
Bacteria and Archaea emerged ….
in the first 2 billion years of the emergence of life
Eukaryotes emerged between ….
2.7 BYA (chemical evidence) to 1.8 BYA (fossil evidence)
The earliest eukaryotic fossils were….
Proterozoic unicellular eukaryotes, 1.8 billion years old
Eukaryote multicellularity evolved ….
many times from unicellular ancestors
What are some benefits to multicellularity?
- better competitors
- specialization of cells
- no reliance on a single cell to survive
- better defense against mutation
What are some cons to multicellularity
- way higher energy costs
- replication takes much longer
Multicellularity is not a _____ ______character. It has evolved ______ _____ times.
Multicellularity is not a SHARED DERIVED character. It has evolved INDEPENDENTLY MULTIPLE TIMES.
What are 2 hypothesis for why multicellularity may have arose?
- Large size is advantageous
- Left wall of minimum complexity
What is the issue with the “Large size is advantageous” hypothesis for the rise of multicellularity?
- Primary issue with this hypothesis is that larger size is good, but larger cells are disadvantageous
- diffusion in cells is only effective over short distances. If cells are large, resources will not be able to transport well.
What is the “Left wall of minimum complexity” hypothesis?
- hypothesis explaining why multicellularity may have evolved.
- The concept is that you have to have at least a single cell to be alive, you can’t evolve to have less cells if you are unicellular
- thus the only path of evolution was to evolve multicellularity
How might multicellularity have evolved?
- Symbiosis, two cells working together
- Internal division of multinucleate organisms
- coloniality, multiple cells working together eventually evolved through division of labor
What is the most likely hypothesis on how cells evolved to have multicellularity
via coloniality
Not all organisms evolve multicellularity. Why not?
- multicellularity is CHALLENGING to accomplish.
- Many traits to gain over time
What are some of the necessary traits of multicellular evolution?
- must have division of labor with specialized cell types,
- must evolve to have cell adhesion. Cells need to stick together
- Need to have intercellular bridges to move nutrients and signaling molecules for coordination and communication
Why do only clonal lineages evolve complex multicellularity?
- because all the cells have the same genetics, and come from a single cell.
When was the first multicellular animals?
575 million years ago (Ediacaran period)
What is “lagerstatten”?
- a certain set of conditions for exceptional fossil preservation
What are some conditions for lagerstatten?
- rapid burial
- anoxic conditions to prevent decay
- marine organisms with hard parts such as bones, scales
when did the Cambrian explosion begin?
542 million years ago
Why was there reduced fossilization prior to the cambrian explosion?
- lack of exo and endoskeletons
- mostly soft bodied animals prior to cambrian
what are the three major hypothesis for the rapid increase in diversity that caused the cambrian explosion?
- Geological
- Geochemical
- Genetic
How did geological means cause the cambrian explosion?
- Continental change, and continents splitting up, increasing the area of continental shelf
- caused a change in atmosphere and climate conditions, nutrient cycling
- in addition, continents splitting up lead to allopatric speciation when species were separated
How did geochemical means cause the cambrian explosion?
- continental changes lead to different atmosphere, and an increase in calcium, phosphate, and oxygen
- increasing oxygen lead to higher metabolism and growth
- Ca and Po4 lead to biomineralization and an increase in nutrients –> creation of skeletons, and protective structures
How did genetic means cause the cambrian explosion?
- the increase in biomineralization lead to endo and exoskeletons.
- body innovation lead to a ‘predator-prey arms race’, which lead to rapid diversification
What are the intrinsic causes that lead to the cambrian explosion?
- largely genetic changes
- rapid change in genes regulating caused: body plan organization, and exoskeletons/locomotion
- additionally, the evolution of the Hox gene complex lead to developmental flexibility
What are extrinsic causes that lead to the cambrian explosion?
- geological and geochemical changes
- the changes in the environment lead to changes in climate, and nutrient availability
- eventually leading to genetic diversity
Geological and geochemical changes in the cambrian explosions caused ________, while genetic changes caused _________
Geological and geochemical changes in the cambrian explosions caused OPPORTUNITY, while genetic changes caused INNOVATION.
What happened to the early ‘experimental’ body plans from the cambrian explosions?
- normal extinction could account for some of the loss. Competition, predation, failure to adapt to environments all could leas to natural selection and extinction.
- However, the end of the cambrian was also marked by a major extinction event, and when environmental conditions suddenly change, it may be random who survives and directed future evolution
What happened directly after the Cambrian?
- The Ordovician!
- things escaped water and invaded land
the first terrestrial plants arrived in
the late ordovician or early silurian
Tetrapod vertebrates originate in the ____ ______ and radiation significantly in the _______.
Tetrapod vertebrates originate in the LATE DEVONIAN and radiation significantly in the CARBONIFEROUS
Why was there a paleozoic ‘plateau’, and then sudden post-Paleozoic increase?
- Paleozoic diversity ‘plateau’ occurred because not much was changing environmentally
- The step increase in diversity in post-paloezoic is thought to have happened because there was fragmentation of the continents again, leading to another increase in opportunity
What are some possible explanations for major changes in dominant taxa
- competitive advantage of superior life forms
- extinction events opened new opportunities for ‘survivors’
- fragmentation of continents/ocean basins yield new opportunities
What is GOBE?
Great Ordovician Biodiversification Event
What was the Cambrian explosion?
- diverse and complex marine life suddenly ‘exploded’ over a relatively short span of geological time
What was the great ordovician biodiversification event? what was the event?
- an event that lead to great diversification of previous animals
- this was thought to be caused by multiple asteroid impacts, leading to changing environmental conditions, which lead to new opportunities and niches for organisms to fill
Paleontology provides evidence for
- gradual changes within lineages
- transitional fossils which test our hypothesis
- major transitions in succession and origins of new groups
