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Evolution:
Primordial Earth
Background information about Darwinian evolution.
Includes information about Darwin's original theory of evolution by means of natural selection.
What Daniel Dennett (philosopher) thinks of evolution.
Think Quest
Go to the Think Quest page.
The infant Earth that is pictured by scientists today basks in a sun that shines with 70% of its present power. A world with no free oxygen in the atmosphere and no sounds other than the wind, the hissing lava against water and meteorites hitting the Earth. No plants, no animals, no bacteria or viruses existed on Earth. From that point on, scientific opinion vastly diversifies. As of now, there are three possibilities for the start of life on Earth. Whatever the circumstances, once organic compounds organize themselves into something that is capable of self-replicating, Darwinian evolution is possible.
In 1952, Stanley Miller, the father of prebiotic chemistry, conducted an experiment that simulated conditions on Earth before life arose. He simulated his version of a primordial Earth by creating a network of glass flasks and tubing. One flask held an electric toothbrush that generates 100,000 volts. In the same flask as the electric toothbrush, Miller placed methane, hydrogen and ammonia to represent he alleged atmosphere. In a lower flask, a little pool of water represented the oceans of ancient Earth. When the electric toothbrush let out its volts, the result was a rich broth of amino acids, used by all known creatures as the building blocks for proteins. From this experiment, Miller deduced that life could be created with an ocean, an atmosphere and some lightening. However, many scientists now suspect that primordial Earth's atmosphere is different from what Miller had supposed. Scientists nowadays believe that the atmosphere consisted of carbon dioxide and nitrogen. When they tried to spark this atmosphere, they came up with the equivalent of a few drops of food coloring in a swimming pool of water. This problem, however, could be solved with asteroids, comets or meteorites that carry organic molecules.
It still remains a subject under debate, though, exactly in what condition the first stirrings of life arose. Life may have started in a ball of ice, a pond, a cauldron or even a completely different planet.
Although carbon dioxide in the atmosphere would have made the "green
house effect" effective on Earth, (considering the fact that the colder
the temperature the more stable the compound) many scientists today imagine
a global winter. Interplanetary debris, atmospheric reactions and hydrothermal
may have provided compounds such as cyanide, ammonia and formaldehyde. These
then collect and combine within a lattice of ice creating an amino acid
called glycine (amino acids are used by all known creatures as the building
blocks of proteins). A huge meteorite impact ultimately could have thawed
this frozen world.
Charles Darwin envisioned the first stirrings of life on a temperate world in a small body of water. Glaciers, volcanoes, geysers and interplanetary debris can supply compounds to water that collect in small bodies of water such as a pond or a basin. Further concentrated compounds in the water (internal surfaces of sheet-like minerals) attract certain molecules. Two aldehyde phosphate molecules would be able to unite forming a sugar phosphate, a possible predecessor of RNA.
In a steamy world after accretion, Earth may have been a ball of fiery magma. Volcanoes, geysers and hydrothermal vents would have leached out vital compounds where reactions can ensue. Pyrite, carbon monoxide and a methyl group combine and your one step in to the formation of activated acetic acid (a vital chemical for synthesizing other organic compounds).
As of now, the question is whether primordial Earth was freezing, temperate or steamy and what elements existed in the atmosphere. Scientists are coming closer to a conclusion, but no one has solved the mystery of what infant earth looked like.