1copyright cmassengale modern ideas on the origin of life
TRANSCRIPT
1copyright cmassengale
Modern Ideas on the Origin of Life
Formation of the Earth
• 4.5 billion years ago• Cosmic debris
attracted to one another
• Collisions = heat = melting
• Atmosphere = hydrogen cyanide, CO2, CO, N2, H2S, H2O
Formation of the Earth
• 3.8 billion years ago
• Cooling = oceans
• Brown oceans due to dissolved iron
• Life Begins– Prokaryotic,
anaerobic, heterotrophs
First Organic Molecules
• 1920s – Oparin and Haldane
• Earth’s early atmosphere had all elements necessary to cause reactions producing organic molecules (amino acids)
• Gases, UV light, lightning
PRIMORDIAL SOUP HYPOTHESIS
First Organic Molecules
• 1950s – Miller and Urey
• Suggests how mixtures of organic compounds necessary for life could have come from simpler compounds present on primitive Earth
First Organic Molecules
Animation of Miller and Urey’s Experiment
• http://ircamera.as.arizona.edu/NatSci102/movies/anim_miller_urey_exp.gif
• Proved amino acids could be produced in primitive Earth’s conditions
Early Life
- the first cells were probably heterotrophs that simply absorbed nutrients and ATP from the environment.
- as these substances became rare, there was strong selection for cells that could manufacture their own energy storage molecules.
Early Life
- the second type of cells were probably like green-sulphur bacteria which in the presence of sunlight, are able to photosynthesize.
Early Life
- the evolution of oxygenic photosynthesis was MAJOR. It allowed life to exploit more habitats. These stromatolites, which date to > 3 bya are microbial communities.
Early Life
- about 2.3-1.8 bya, the concentration of oxygen began to increase in the ocean. Oxidized iron shows rust bands in sediment.
Endosymbiont Theory
• 1966- Lynn Margulis • Explains origins of
mitochondria and chloroplasts
• Mitochondria and chloroplasts were once free-living bacteria which had a mutualistic relationship with another bacterium
Endosymbiont Theory
• Mitochondria and chloroplasts are same size as bacteria and contain similar structures (DNA, ribosomes) and reproduce by binary fission
infolding of membrane
Endosymbiosis - mitochondria and chloroplasts (Margulis - 1970's)
Evolutionary Tree – shows evolutionary pathways of living organisms
So, reconstructing the patterns of relatedness among these ancient life forms is difficult.
Different genes give different patterns of relatedness among domains