The Reign of the Prokaryotes

Here we pick up from Saturday, with the formation of the planets in our solar system and the continents on our planet, Earth. Most of the junk flying around in space had been gobbled up by the Sun, Jupiter, and the rest of the continents. The Earth finally was freed from a constant bombardment of comets and good-sized asteroids. Damaging asteroid strikes did not disappear; they just became much less frequent.

Volcanoes erupted regularly. Between those violent crashes and the volcanoes, the earth’s boiling hot surface included an atmosphere of methane, steam, hydrogen sulfide (the rotten egg smell), and carbon dioxide, in addition to nitrogen and carbon dioxide. No oxygen, though! The earth finally cooled a little, turning the steam into water. Rain poured down for a long time, filling the oceans.

Around four billion years ago, conditions were cruel. The atmosphere and the oceans were a chemical soup. The oceans were green and acidic, the skies orange with high levels of methane, ammonia and carbon dioxide. A complete list of all the ingredients of both the ocean and the atmosphere are not known for certain, but any living plant or animal of today would immediately die if placed in that environment.

Despite these horrific conditions, life appeared. Out of that fiery, dense Big Bang explosion comes the itty-bitty little particles out of which you, your parents, the ground you walk on, the Moon, the stars – everything! – is made. Little bits of that stuff got together just right and out came the first DNA.

Life begins. In the water. Life’s first DNA. That DNA, though, was NOT simple.

Well-preserved bacteria from the era 3.6 to 3.2 billion years ago was found in Western Australia. General agreement for life’s beginning is 3.7 to 3.8 billion years ago.

What arrived was the earth’s simplest form of life. But what is life?

  • A simple explanation: on one hand are living things, plants and animals; on the other hand, inorganic matter.
  • A more precise definition: Living things take in food, grow, and have wastes; they reproduce; and have DNA.

Those first living organisms were single celled. Biology calls them prokaryotic; “bacteria” is easier to remember.

Here is an introduction to that first life form, the prokaryotes. Each organism was surrounded by a thin membrane. Inside the membrane, nutrients moved around, messages were sent, and a variety of other complex tasks carried out. The instructions for all this action were in the DNA. The DNA directions included how to do those things—move, use food for energy, eliminate waste, and reproduce.

Those first living cells were tiny, tiny, tiny. A piece of paper is about one millimeter thick. Those first cells were 1/1000 of a millimeter! Two examples of prokaryotic organisms today are bacteria and green algae.

Those tiny organisms stored essential genetic information coiled up inside. To create this two-for-one step called reproduction, the cell first had to grow to twice its own size. Then it split into two, creating a matched copy of the original. The process was not really that simple but that is an outline.

Reproduction required no external help. The cell was on its own to grow-split-grow-split- … and on and on. Do not scoff at these prokaryotic cells. They are by far Earth’s most consistently successful organism. The reign of the prokaryotes begins and continues for more than two billion years.

Here is a timeline of the beginning of the story from Big Bang to you.

big bang to you

These little bacteria cells had a little tail; they could move about in the water. Today, they exist in plants and animals as well as in the atmosphere. In your body, they help digest food. They also cause you sickness.

The enquiring mind is saying, “How does science know all this stuff? Do they just make it up?” A complete answer would take a book. Next week, a brief explanation!

Next post: How does science know all this stuff?

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