Origin of Life

Life on Earth has evolved around the chemical versatility of a few atoms, especially carbon. Carbon, hydrogen, oxygen, nitrogen, phosphorus, and calcium form the major chemical scaffolding of biological molecules. Hydrogen, nitrogen, oxygen, phosphorus, and sulfur combined with carbon generated the first group of compounds that eventually formed the chemical basis of life. Other elements, such as iron, magnesium, sodium, potassium, chlorine, and iodine also play specific and vital roles. Some special features of chemistry are used by living systems. These features are:

1. the ability of carbon to combine in so many different ways;
2. the unique properties of water; and
3. the ability of organic molecules to use small amounts of energy efficiently.

A live organism is an open system, continuously exchanging energy and matter with the environment. It is "self-organizing," meaning it takes raw material and reassembles it into complex vital molecules. During this process, life increases internal order (decreases entropy). Thus life builds up information (order) which is then duplicated.

In the Beginning

The early environment on Earth is a matter of conjecture. Piecing together evidence, it is believed now that the environment consisted of high energy events such as volcanic eruptions, continuous torrents of rain, and large amounts of lightning. It is believed that there was little if any oxygen in the atmosphere, and certainly no ozone layer. Therefore, ultraviolet from the sun could reach all the way to the Earth's surface.

<INSERT figure on early environment from Microcosmos?>

Some of our models for the early environment of Earth come from the observation of the atmospheres of Mars and Venus, made by NASA.

Table X shows the major gases in the atmosphere of Venus, Mars and the Earth. Note the difference between the estimate of the composition with and without life on earth.

It has been shown in laboratory experiments that simple carbon-based (organic) molecules are formed under early conditions. In 1953, Stewart Miller, a graduate student of the famous chemist, Harold Urey, simulated the early (prebiotic) atmosphere on Earth--a mixture of ammonia (NH₃), water vapor (H₂O), hydrogen, and methane (CH₄). He bombarded the mixture with electrical discharges to simulate lightning. In a week, he saw some spectacular results: alanine and glycine, two amino acids that form proteins in life forms today (including humans) were formed in the resulting mixture. Under the conditions provided, more complex molecules such as formaldehyde (HCHO), formic acid (HCOOH), and hydrogen cyanide (HCN) had formed. In a water solution these molecules had then reacted with each other to form more complex organic molecules such as acetic acid (CH₃COOH), glycine (NH₂CONH₂), alanine (NH₂CHOHCOOH).

The richness of carbon chemistry and the plethora of carbon compounds form the basis of life on Earth. Carbon chemistry (called organic chemistry) and the function of biomolecules are explained in detail in the section on carbon compounds.

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