On Wednesday, we asked: how does science know all this stuff? The answer: rocks.
Rocks store old information. First, a rock holding such critical information must be found. Once found, then the rock that held that information must be dated. In the rock are elements that have a “nuclear decay” — they shoot off a little energy which basically creates a new element. Time is measured by the amount of the new element in the old rock. The equipment used is pretty sensitive.
Logic also gets involved. If the rock fossils are all single celled, then that rock existed before multicellular life appeared. The single cells are at the lower level; multi-cells one layer up. In a big, broken stone or a cliff with many layers, clearly each new layer appeared after the one below. By piecing all this information together, geologists can make reasonably accurate estimates for timing of ancient events.
When scientists asked, “What happened?” and “What are the steps that made it happen?” the response usually falls back on Charles Darwin’s natural selection interpretation. Most people have heard that term “evolution”; unfortunately, however, a large percentage do not really understand the details. All at once, first life was under attack. The next step (which saves the prokaryotes) in the story is an example of now Darwin’s approach works.
Those first little bacteria were flourishing, thriving on an oxygen-free environment. They were having a jolly time covering the earth. But then — the plot thickens — they came under attack.
What attacked them? Oxygen. Photosynthesis arrived near the middle of the Reign of the Prokaryotes. Bacteria capable of photosynthesis were ingesting carbon dioxide and spewing out oxygen. Soon the atmosphere had a lot of oxygen. To the existing prokaryotes, oxygen was poison; they were dying off in droves. If they all die, well, this story ends and there would be no you or me.
Why didn’t then all die? Darwinian interpretation involves a two-step process.
Those bacteria reproduce by splitting in two. After the split, both parts have exactly the same DNA structure. But random accidents happen; sometimes one of the cells does NOT have exactly the same DNA structure. That oddball cell is called a mutation. So start with the first step: random mutation.
The second step is called natural selection. Change is triggered by those reproductive mistakes. The mutation fights to survive – to find food, to reproduce. Most mutations die off; after all, they happened by chance. But along comes a mutation that CAN survive even if oxygen is in the air. That mutation flourishes, reproduces like crazy, and starts dominating. A change has occurred in that bacteria cell’s DNA. Children who come from this somewhat changed DNA are also better-able to handle oxygen. That new, DNA-altered bacteria thrived. The “random” part is the mutation. The “natural selection” here is that nature selected the bacteria that reproduced and thrived most successfully.
Another question: Did this change occur because of just one mutation in one cell? Many believe that other bacteria, under the same strained conditions, could also have created mutations that could thrive on oxygen and be successful. Perhaps there were hundreds of such mutations and, probably, they were not all exactly the same. They could all a little different BUT all can handle living in oxygen. Over time, they will converge to one big happy family, all of whom have a DNA structure altered in a manner allowing them to thrive on oxygen.
A lot of time had passed, but the Reign of the Prokaryote finally came to an end. In their nearly two billion year dominance, evidence shows that all over the Earth, where there was water, some form of bacteria was growing. Sometimes it made its way onto land.
Soon more complex life will join them on Earth. That more complex cell only formed because two groups of bacteria species joined together, merging permanently.
The beginning steps – life beginning, the new life form flourishing and then a more complex form appears – happened in an environment capable of making dramatic changes. Like it or not, each new life form had to be in harmony with the environment around it. Next week, we’ll look at a sort of short description of how these dramatic environmental shifts happen.
Next post: A look at the dramatic environmental shifts that allowed for a new form of life!
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