49 terms

Origins of Life

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Life on earth date of origin
between 3.5 and 4 billion years ago
Fist living creatures
Prokariotic-like; supported by the fossil record
Spontaneous generation (definition)
The origin hypothesis where organisms come to life directly from non-living matter
Spontaneous generation (origin)
Origin hypothesis created by Greek philosophers; Aristotle believed that life arose from "slime". Dis-proven by Louis Pasteur with meat in 1861.
Inorganic model of life origin (Definition)
Origin of life hypothesis where complex organic molecules arose slowly from pre-existing, non-organic and self-replicating silicate crystals in solution
Inorganic model of life origin (Experimental Evidence)
Able to produce polymers from dilute solutions of monomers by dripping the solution into hot sand, clay or rock.
-Evidence has largely been inconclusive so far.
Inorganic model of life origin (Key minerals)
Clay played an important role because monomers bind to the clay and concentrate. Pyrite (FeS2) also important because of its formation in sulfide-rich marine sediments and in high temperature anaerobic conditions where it could reduce CO2 to organic compounds.
Panspermia hypothesis
Origin hypothesis where the first organic compounds reached our planet from meteorites and comets that collided with Earth during the Precambrian period
Biochemical Model
Origin hypothesis where life is produced through a series of organic chemical reactions to form more complex biomolecules from simpler organic forms. First proposed in the 1920's by Oparin and Haldane.
Hydrothermal Vent Hypothesis
Life originated around the hydrothermal vents
last universal common ancestor (LUCA)
hyperthermophile single cell organism evolved in hydrothermal vents
Dificulties in proving the biochemical Hypothesis
around the origins of life there was:
-No or very little atmospheric oxygen
-Intense energy provided by UV radiation, meteorite collisions, volcanic activity and lighting.
-The first living organisms were the products of abiotic biochemical evolution.
stage 1 of biochemical evolution
Abiotic synthesis and accumulation of small organic molecules.
stage 2 of biochemical evolution
Joining of these building blocks into polymers (i.e. amino acids and proteins)
stage 3 of biochemical evolution
Formation of droplets (protobionts) from aggregates of abiotically produced molecules
stage 4 of biochemical evolution
Origin of heredity during or before the appearance of protobionts.
Oparin/Haldane hypothesis
postulated that the reducing atmosphere and greater UV radiation on the infant Earth favored chemical reactions that could produce complex organic molecules.
(Biochemical Model)
Stanley Miller and Harold Urey
tested the Oparin/Haldane hypothesis by simulating the early precambrian conditions of our planet. Experiment produced some amino acids and other organic molecules.
Miller-Urey experiments (Results)
do NOT explain how life originated! They

-indicate the chemical environment in which life originated.

-explain why the formation of complex organic molecules from simpler building-blocks molecules may have been common
Primordial soup
dilute solutions of simple organic molecules where the first chemical reactions probably occurred
RNA world
RNA is the precellular entity and the time between non-life and life. lasted for 100-400 million years between 4 and 3.5 billion years ago.
Properties of RNA that make it a likely candidate as the initial carrier of genetic information
1) RNA can behave as a catalyst and ribozyme.
2) RNA polymerization and replication can happen in vitro.
3) Genome of certain viruses is purely RNA-based.
4) Universal importance of RNA during protein synthesis in all living organism.
5) Single-stranded RNA can fold in different 3D configurations (providing different functions).
Steps of RNA evolution
-Production of a 'protocell' which combined an RNA replicase with a self-replicating vesicle
-production of a cell by the addition of a living function.
Precambrian
Hadean, archaean and proterozoic eons
Hadean
(4.6-4 bys) earth was initially a molten mass which later cooled, lots of asteroids
Oldest rock
4.28 billion years old from canada
Archaean
(4-2.5 bys) A cooler, anoxic world and rich in atmospheric methane gas. presence of cyanobacteria?
First sedimentary rock
Rock erosions by wind and water supplied the material during the Archaean (3.8 bys).
Proterozoic
(2.5bys-542 Mys): oxygen levels in the atmosphere begin to increase up to 0.1% of present oxygen levels (~21%) due to the "Great Oxygenation Event" (GOE)
"Great Oxygenation Event" (GOE)
May have been dues to abundant methane gas which, when decomposed releases free hydrogen molecules that contribute to the ozone layer.
Bacteria
these are the most diverse and widespread prokaryotes
Archaea
prokaryotic single cell organisms. Most live in extreme environments
Eukarya
these organisms range from single cell to multicellular
Oldest Fossils
single cell prokaryotic organism collected from stromatolites from 3.5 bya
Stromatolites
laminated domes of carbonate sediments constructed by colonies of bacteria and cyanobacteria living in salty environments.
Oldest fossil (Not stromatolite)
Single celled thread-like filaments that come from sulfide deposits similar to the ones currently found in hydrothermal vents
Eukaryotes
may have been descendants from symbiotic relationships between ancient prokaryotic cells
Grypania
photosynthetic alga; first eukaryote to appear in the fossil record about 2.1 bya
The serial endosymbiosis hypothesis
suggests that certain endosymbiotic prokaryotic species lived within larger prokaryotes and later evolved into eukaryotic organisms
Mitochondria
appear to be the descendants from prokaryotic aerobic heterotrophs
Chloroplasts
may be descendants from photosynthesizing prokaryotes such as cyanobacteria
Evidence for the serial endosymbiosis origin of mitochondria and chloroplast
-the appropriate size for prokaryotic cells
-Inner membranes and transport systems similar to prokaryotes
-Replicate similar to binary fission
-DNA is circular and not associated with histones
-Contain their own tRNA
-Ribosomes are more similar to prokaryotes
Problems with the serial endosymbiotic theory
-Neither the Archaea nor Bacteria domains appear to be clearly ancestral to the Eukarya;

-Biomarker steranes derived from sterols (synthesized only by eukaryotes) are found in sedimentary deposits dated to 2.7 bys.
'protoeukaryote host theory"
the ancestral eukaryote already had a nucleus before engulfing an energy-transferring aerobic prokaryote which later became the mitochondria.
Plants
thought to have evolved from green algae
Animals and fungi
believed to have evolved from groups of heterotrophic cells
Sexual Reproduction
evolved first before the appearance of multicellularity
Bangiomorpha pubescens
oldest fossils of multicellular organism from the shallow marine Carbonates of eastern Canada dating to 1.2 bys
Ediacaran invertebrates
The oldest multicellular animals; completely soft-bodies; from 580 mys