Abiogenesis & the Histroy of Life (PP18) Flashcards
how old is the world? How old is cellular life?
Our world is 4.54 billion years old
It is estimated that cellular life originated sometime between 3.5 & 3.7 billion years ago
Some recent findings may push that as far back as 4.1 billion years ago
how was the early earth different than now
Earth’s atmosphere was likely thinner & had no ozone layer (so more UV radiation)
Composed primarily of H2O, H2, CH4, NH3
Planet was likely warmer (but perhaps not hot)
define abiogenesis
Genesis of biota from an abiotic system (i.e. getting life from of non-life)
how did we first synthesize organic compounds
Experiment conducted by S. Miller & H. Urey
- Took simple molecules (H2O, H2, CH4, NH3) & combined them in an airtight flask
- Exposed to an electrical spark (to mimic lightning)
- Resulted in formation of a large # different biomolecules (some similar to the amino acids found today)
- Formation of such biomolecules was an essential first step towards abiogenesis
what does Polymer formation require
a series of dehydration reactions
what helps polymer formation?
what makes polymer formation more difficult?
catalysts (e.g. polymerases, ribosomes)
Even more difficult to form polymers if biomolecules are free-floating
what is the hypothesis about the formation of polymers
Hypothesis:
Monomer attached to a solid surface (e.g. clay or rock)
Dehydration may then have occurred if this surface was in a hot environment → heat could facilitate the formation of a polymer
where are the two option for where life first arose?
Deep-sea hydrothermal vents
vs.
Shallow geothermal pools
cell membranes are due to what
cell membranes form due to the amphipathic nature of phospholipids
the bilayer structure in our cells is the result of what
the result of specific positioning of biomolecules - physical properties, not chemical interactions
what is the hypothesis about thee formation of membranes
Hypothesis:
If specific type of amphipathic biomolecule present in the correct environment, it could spontaneously close to form a cell membrane
Should membrane form around polymers, then primitive cell may have been produced!
what is a protobiont
aggregates of abiotically-produced molecules surrounded by membrane / membrane-like structure
do protobionts exhibit any characteristics of life? if yes, which
yes
Reproduction
Metabolism
Internal chemical environment different from the exterior surroundings
true or false: protobionts can form spontaneously from abiotically-produced organic compounds
true
give one xample of protobionts forming spontaneously
small membrane-bounded droplets (liposomes) can form when lipids or other organic molecules added to water
explain simple reproduction in protobionts
Simple reproduction.
Liposome is “giving birth” to smaller liposomes (LM).
explain simple metabolism in protobionts
Simple metabolism.
If enzyme are included in solution from which droplets self-assemble, some liposomes can carry out simple metabolic reactions & export the products.
what is the hypothesis of how a cell, a self replicating life form came about
If ribozyme-like biomolecule can form through polymerisation within a membrane, then a self-replicating organism could have formed
why would rna be a good candidate
Ribozymes = RNA molecules capable of performing different chemical reactions
Some ribozymes can form copies of themselves through polymerisation
have the ability to self splice
-Can make complementary copies of their own sequence or other short pieces of RNA
-Early protobionts with self-replicating, catalytic RNA would be more effective at using resources → increase in number via natural selection
can these hypothesis of life be proven
no, we were not there and cannot go back in time
why can abigenesis be possible even though seems impossible
Even if the process seems very unlikely, one must take into consideration the enormous timescales
Even with odds of one-to-a trillion, with enough time, the possibility of abiogenic events would eventually become plausible
what is the “evidence” that this could happen
The steps described previously have been mimicked in research labs (i.e. they are indeed possible)
what are stromatolites
earliest fossils
Stromatolites = rock-like structures composed of many layers of bacteria & sediment
earth as a clock
Life in 24h: If the planet was formed at 00:00, the first life appeared at ~04:00, the first multicellular life at ~17:00, and humans at ~23:59:30
LOOK AT SLIDES FOR CLOCK
what are the 4 eons
4 eons: Hadean Archaean Proterozoic Phanerozoic
which 3 eons are part of precambrian
Hadean
Archaean
Proterozoic
each eon marks what
Mark major changes in the composition of fossil species
Explain the hadean eons and its time period
Hadean (4.6 – 4.0 Gya)
Formation of the planet
No life
explain the archean eon and its time period
Archean (4.0 – 2.5 Gya)
Cooling allows continents to form
Life first appears
Atmosphere still lacks free oxygen
explain the proterozoic eon and its time period
Proterozoic (2.5 – 0.5 Gya)
Atmosphere becomes oxygenated (due to life)
Multiple glaciations (Slushball Earth)
Appearance of eukaryotic life & then multicellular life
explain the phanerozoic eon and its time period
Phanerozoic (500 Mya – present)
Hard bodied organisms appear (fossils)
Complex plants, insects, & tetrapods appear
Plants arrive on land, then animals
what are the 3 eras in the phanerozoic eon
Paleozoic Era (541 – 252 Mya)
Mesozoic Era (252 – 66 Mya)
Cenozoic Era (66 – 0 Mya)
explain the paleozoic era and its time frame
Paleozoic Era (541 – 252 Mya)
Includes Cambrian period (explosion of diversity)
Appearance of arthropods, molluscs, fish, amphibians, synapsids (e.g. reptiles), & diapsids (e.g. mammals)
explain the mesozoic era and its time frame
Mesozoic Era (252 – 66 Mya)
Dinosaurs! (Triassic, Jurassic, Cretaceous)
Appearance of flowering plants & coral reefs
Ended with Cretaceous-Paleogene (K-Pg) extinction
explain the cenozoic era and its time frame
Cenozoic Era (66 – 0 Mya)
“Age of Mammals”
Includes Quaternary Period (now)
fossil record shows several occasions when….
when global environmental changes were so rapid & disruptive that a majority of species went extinct
what are the two mass extinctions
Permian & Cretaceous
explain permian extinction
Permian extinction caused 96% of marine animal species & 8 of 27 orders of insects to go instinct
Thought to have been caused by enormous volcanic eruptions
did the Earliest types of photosynthesis produce oxygen
no
where did Oxygenic photosynthesis probably evolve
~3.5 billion years ago in cyanobacteria
why was oxygen bad?
why was it good?
Oxygen posed a challenge for life (toxic to obligate anaerobes)
Offered up new opportunities & provided selective pressure (eukaryotes may have had an advantage)
what is the theory of endosymbiosis (complex eukaryotic cells evolving from much simpler prokaryotic cells)
Theory of Endosymbiosis (Mereschkowsky 1905 & Margulis 1972):
- mitochondria & plastids were formerly small prokaryotes living in larger host cells
- Prokaryotic ancestors of mitochondria & plastids probably gained entry to the host cell as undigested prey or internal parasites
- In the process of becoming more interdependent, the host & endosymbionts became a single organism
what is the benefit of endosymbiosis
Benefit: extra energy!
what is key evidence for endosymbiosis
Key evidence for endosymbiotic origin of mitochondria & plastids
- Similarities in inner membrane structures and functions
- Both have their own circular DNA
- Both have ribosomes
