Transcript Prebiotic Evolution

Prebiotic Evolution
Chapter 18
Until about 300 years ago people believed in
the idea of spontaneous generation –
that life comes from non-living material.
1668 Francesco Redi proved that magots
did not come from rotting meat.
Could microorganisms arise spontaneously?
1864 Lois Pasteur finally disproved this idea.
How did life arise on Earth?
1. “panspermia” – life arrived here from
outer space
– Not a testable hypothesis
2. Prebiotic evolution – life arose from nonliving matter
For prebiotic evolution to take place,
conditions on the early Earth must
have been very different
1. The atmosphere contained virtually no
free oxygen
2. There was no life on Earth
3. Life had 300 million years to get its act
together
• The early Earth’s atmosphere probably
had hydrogen gas, ammonia, methane,
and traces of carbon dioxide and hydrogen
sulfide.
– No rust
– No ozone – UV radiation may have been a
driving force
– Heat from the earth and lightning also
provided energy to make chemical bonds
• Organic molecules could have come from
comets, asteroids or meteors.
• Either way, oceans may have been full of
organic molecules.
• More complex molecules needed more
help to form, probably on clay and metal
ions at the edges of oceans.
• Can make peptides of up to 50 amino
acids in length.
• Glucose, ribose, deoxyribose and other
sugars form from formaldehyde (CH2O)
when exposed to UV radiation.
• Adenine forms from hydrogen cyanide
(HCN) and was probably the first base to
form.
• Molecules had to come together in an
organized fashion.
• Polysaccharides form coacervates in
solution.
– Membrane-like boundary
– Act like cells
– Absorb molecules and release products
– Form new spheres by budding
First information carrying molecule
• Was probably RNA since it does not need
enzymes or a primer
– RNA can act as an enzyme
The first cells
• Were heterotrophs feeding off organic
molecules in the oceans
• Used fermentation – pathway common to
all cells.
• Cyanobacteria were the first to produce
free oxygen
• Mitochondria came after
• Endosymbiotic theory
– Endosymbiosis
– Mitochondria, chloroplasts, flagella, nucleus
– Spirochete
– Thermoplasma acidophilum
Cyanobacteria