The Chemistry of Life

The universe is about 15 billion years old. Earth, like other planetary bodies of the solar system, is about 4.6 billion years old, but the fossil record shows that Earth was devoid of life for some hundreds of millions of years after it coalesced from the solar nebula. The earliest fossils are of very simple organisms, bacteria and blue-green algae, dated at 3.1 billion years old. How did they get there?

Some time before these first life forms arose, during the earth's first several hundred million years, the simple molecules present (nitrogen, oxygen, carbon dioxide gas, ammonia, and methane) somehow formed into the more complex amino acids that are the chemical building blocks of life. Most scientists believe that the turbulent youth of the earth provided the energy that caused the transformation of simple elements and compounds into the building blocks of life. Also remember that, in its infancy, the earth was orbited by a much closer moon, so that once liquid water was present on its surface, the tides would have been enormous— perhaps 1,000 feet up and down as the planet rotated once every 6 (not 24) hours! This vigorous mixing of the primordial soup (shaken, not stirred) may have had a profoundly creative effect.

Astro Byte

Volcanic activity on the early Earth sent many gases coursing into the atmosphere. Its early carbon dioxide atmosphere literally arose from within. The earth had sufficient mass to hold onto the heavier molecules in its atmosphere, but not the lighter hydrogen and helium.

Astro Byte

Volcanic activity on the early Earth sent many gases coursing into the atmosphere. Its early carbon dioxide atmosphere literally arose from within. The earth had sufficient mass to hold onto the heavier molecules in its atmosphere, but not the lighter hydrogen and helium.

Once amino acids and nucleotide bases were available, the next step up in complexity would have been the synthesis of proteins and genetic material. The DNA molecule is made up of what are called nucleotide bases, or genes. Strung together, the genes tell our cells what to do when they reproduce, and make us different from, say, earthworms. The DNA molecule is the most durable, portable, and compact information storage device we know of. We are just beginning to unravel its mysteries.

There may be plenty of planets similar to the earth—that is hard to deny. But it is extremely difficult to estimate the likelihood that the molecules on any given planet will combine to form amino acids and nucleotides, let alone proteins and DNA (which are made from amino acids and nucleotide bases, respectively). Here is where the questions, and the debates, begin.

All life on Earth is carbon-based. That is, its constituent chemical compounds are built on carbon combinations and, furthermore, developed in a liquid water environment. Even creatures such as ourselves, who do not live in water, consist mostly of water. If life on the earth developed first in the oceans, we, billions of years later, still carry those oceans within us.

Close Encounter

Close Encounter

In 1953, scientists Stanley Miller and Harold Urey decided to see if they could duplicate, experimentally, the chemical and atmospheric conditions that produced life on the earth. In a 5-liter flask, they replicated what is thought to be the earth's primordial atmosphere: methane, carbon dioxide, ammonia, and water. They wired the flask for an electric discharge, the spark intended to simulate a source of ultraviolet photons (lightning) or other form of energy (such as a meteor impact shock wave). The Miller-Urey Experiment didn't produce life—no Frankenstein's monster—but, remarkably, it did create a collection of amino acids, sugars, and other organic compounds. Thus the Miller-Urey Experiment implied an extension of the assumption of mediocrity. Not only could we reasonably conclude that there are other similar planets in the Galaxy, but also that they must have the chemical elements necessary for life, and energy alone could trigger the synthesis of the building blocks of life.

Telescopes Mastery

Telescopes Mastery

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