Important Theories about the Origin of Life Help (page 2)
Introduction to the Important Theories about the Origin of Life
Recall that life begins at the cell level. It is now appropriate for us to ask, “Okay, we know what life is. But where did it come from? And did life forms always look the way they do on present-day Earth?”
Before life, and even before the planet Earth, the Universe or Cosmos ( KAHZ -mohs) began as a “Big Bang.” About 15 billion years ago, one or more huge, noisy “Bangs” (explosions) of dying stars created giant clouds of dust and gas. Out of such swirling clouds came our “sun” (sol) and the solar ( SOH -lar) system of planets orbiting around it. The creation of our solar system was an important example of Cosmic ( KAHZ -mik) Order – a pattern of organization that occurs within the Universe.
The third planet from the sun – the Earth – appeared approximately 4.5 billion years ago. In the beginning, the Earth had a boiling-hot surface of liquid rock. But even at this early stage, carbon, hydrogen, and many other chemicals necessary for life, already existed.
As the planet cooled, a thin crust of hard rock formed upon the surface. Frequent eruptions of volcanoes forced gases out above this surface crust, thereby creating the atmosphere. The atmosphere is a 1-mile-thick blanket of gases surrounding the Earth. The early atmosphere contained water (H 2 O) molecules in the form of water vapor, which was belched out by the volcanoes. Eventually, the surface cooled, and the water fell as rain. The rain pooled and filled vast surface canyons, giving rise to the first oceans. In addition, the cooling triggered the creation of oxygen (O 2 ) molecules.
Somewhere between 4 billion and 3.5 billion years ago, life probably began within the oceans. Biologists sometimes poetically call this great event the Dawn of Life. Figure 3.1 diagrams A TIME-CLOCK FOR ORDER. Notice that the CLOCK starts things off at midnight, representing 5 bya (billion years ago). As the hand of the CLOCK turns, the number of years from the present-day Earth decreases step-by-step from 5 bya. Each mark on the clock face represents a time span of 0.25 bya or 250 mya (million years ago). The numbers 4, 3, 2, and 1, consequently, represent 1 billion years ago, each. The appearance of the Earth, for instance, is marked about half-way between 5 and 4 (or 4.5 billion years ago). The Time-Clock sounded an alarm, in a sense, and woke up the Earth, at approximately 4 bya. The alarm rang out loudly, because it announced the Dawn of Life. And ever since this dramatic time, Biological Order has been present. It has continuously been reflected within the living things of our world.
Spontaneous Generation and The Modern Theory Of Biogenesis
Spontaneous Generation: Life Coming Out Of Nowhere
One of the theories attempting to explain the appearance of living things (and their associated Biological Order) is spontaneous generation . According to this theory, life is “produced” (generated) “automatically” (spontaneously) from non-living things. For many centuries, it was commonly assumed that a living fish, for instance, could arise “spontaneously” from the mud in the bottom of a lake! And people naively thought that rotten meat was somehow “spontaneously” transformed into swarms of living flies!
A scientist named Francesco Redi ( REH -dee) threw doubt upon the Spontaneous Generation Theory in the 1600s. Redi demonstrated that when rotting meat is covered with a mesh, no flies come out of it. Yet, numerous people still believed that spontaneous generation produced the great variety of micro-organisms ( MY -kroh- or -gan-izms) – “tiny organisms,” such as bacteria.
Another scientist, Louis Pasteur (pas- STER ), finally showed (in the mid-1800s) that micro-organisms did not spontaneously generate. Pasteur boiled a rich broth and kept it in a glass flask with a curved neck for well over a year. The curved neck prevented any micro-organisms from reaching the broth, so the broth remained clear and free of micro-organisms. If any micro-organisms had spontaneously generated within the broth, they would have turned the broth cloudy.
The Modern Theory Of Biogenesis
After Pasteur’s experiment, the old idea of spontaneous generation gave way to the modern Theory of Biogenesis ( buy -oh- JEH -neh-sis). Biogenesis is the theory that “life” (bio) is “produced” (genesis) only from other things that are already alive. Two living male and female human beings, for instance, can mate and produce offspring that are also alive.
But our present-day observations about biogenesis still don’t answer the question, “How did the very first life come into being on our planet?” Most evidence seems to point to a primordial (pry- MORE -dee-al) soup on the surface of the early Earth. Primordial means “first in order”; that is, existing first before other things. The basic idea is that a primordial soup of complex organic compounds existed within the early oceans. Under the right conditions, such as the input of lots of energy from lightning striking the water and volcanoes spewing hot lava, these complex organic chemicals combined together and acquired a membrane around themselves. After this, they somehow became alive. Perhaps these first primitive micro-organisms were a species of ancient bacteria. According to the Theory of Biogenesis, these ancient bacteria eventually gave rise to all other living things on our planet.
Practice problems for these concepts can be found at: From Dawn To Darwin Evolution Test
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