The Origin of Life
The Earth’s Beginnings
- Scientists believe that the Earth was first formed
as a molten mass about 4.5 billion years ago.
- As the Earth’s crust cooled, water vapor in the
atmosphere condensed into oceans.
- Minerals from the Earth’s crust started to dissolve
in the water. This formed the Primordial Soup.
- The atmosphere contained H2, H2O, CH4, and
NH3. NO FREE OXYGEN! The atmosphere was
reducing.
How Life Got “Started”
- Lightning, heat, and UV radiation supplied energy for
random bonding to make inorganic molecules into
organic molecules.
- Organic molecules began to slowly build up over time.
- Since the atmosphere was reducing, these molecules
were very stable and they did not break down easily.
- After a while, several macromolecules had been
formed and covered by protective spheres.
- Think about phospholipids and hydrophobic/philic
interactions, polar molecules…
Stanley Miller’s Experiment
- In 1953, he set up an experiment that used the gases
from Earth’s early atmosphere (H2, H2O, CH4, and NH3)
to model early conditions on Earth.
- Miller zapped the gases with electricity to see how the
energy would affect the bonds of the molecules, like
lightning used to on early Earth.
- He ended up with some amino acids, lactic acid, and
adenine.
The Development of Life
- The first prokaryotic cells emerged about a billion years after the
formation of the Earth.
- These cells were anaerobic heterotrophs (remember, no Oxygen in
the atmosphere…)
- Eventually, cyclic photosynthesis evolved, allowing non-cyclic
photosynthesis to evolve after that.
- This released Oxygen gas (O2) into the atmosphere, where it reacted
to form the Ozone (O3) layer, providing protection from UV rays.
- Now that the atmosphere contained Oxygen, aerobic respiration
could evolve.