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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