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Life

© 1985 by Andrew J. Morris

The land that was eventually to become Larimer County probably came into existence some four billion years ago, as part of the lighter continental crust of our plante cooled and solidified. Because the continents do move, the location of this particular piece of earth could have been anywhere on the globe. It would have been a harsh and alien place at that time, characterized by lifeless rock, a thin oxygen deficient atmosphere and intense heat. Volcanic activity was much more intense than anything we have on Earth today. Not only did life not exist on the land, but life as we know it could not survive in that hostile environment, primarily because of intense ultraviolet solar radiation.

Elsewhere on the planet, in the cool depths of the ocean where the water blocked out the harmful ultraviolet light, life came to be. Complex molecules capable of self reproduction began to multiply, and having no competition from other life forms, flourished. Occasionally the replication was imperfect, so that the new molecular structure differed slightly from the old, giving rise to diversity.

Being different from one another, in however minor a way, meant that some of these simple creatures had an advantage or disadvantage under particular circumstances. Since those dircumstances, or environments, differed from place to place and time to time, different life forms tended to prosper in different places and times. Increasingly complex life forms tended to be more successful than their simpler antecedants, and so supplanted them. Over time life grew in complexity and diversity.

Just how the earliest self replicating molecules came to be is the subject of much speculation and debate. All life as we know it is based on complex carbon molecules, so it is fairly safe to say that the first living molecules were carbon based. The recent discovery of surprisingly complex carbon molecules in space has given rise to the theory that the most basic and simple life forms may exist in space, the product of super-novas perhaps. These simple life forms would be absorbed (eaten) by more complex life forms if they were to fall into todays Earth, but on the lifeless planet some three and a half or four billion years ago, they could thrive. Even if there are no self replicating molecules in space, the complex carbon molecules that have been identified would make the perfect building blocks from which life could form here on Earth.

At some early stage in the history of life on the planet, life forms diverged into two major forms. One group evolved the capacity for photosynthesis -- these were ancestral algae, the precursors to all plant life. The other group derived its energy from the simple trick of consuming the first group, and evolved into animal life.

The greatest diversity and richness of life forms developed where conditions were most favorable, such as the shallow waters of continental shelves. When the Earth's land masses coalesced into a single great continent, the rate of evolutionary change slowed, since there was less total shoreline area. When the land mass split up again into many smaller continents, the pace of evolutionary diversification increased.

Plant life had an important effect on the planet wide environment. In the process of photosynthesis, plants absorb carbon dioxide and release oxygen. As the seas became green with early plant life, much of the oxygen being released escaped into the atmosphere. Not only did this give rise to the oxygen rich atmosphere necessary for animal life on the surface, but complex chemical reactions in the atmosphere formed ozone, an oxygen compound. Ozone has the fortunate property of absorbing ultraviolet radiation. As more ozone formed in the atmosphere, it collected into a high layer in the upper atmosphere. This ozone layer screens out most of the suns's ultraviolet rays, making the surface of the Earth habitable. Thus as life continued to evolve and diverge, some forms moved out of the oceans to conquer a new environment -- the land.

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