Once upon a time in a galaxy……well right here, we evolved. In fact there is evidence everywhere. So much so that I want to go over it. Not just the evidence for evolution, but a lot of how and why.
I often get the age-old question of how life began. Well I will give you a picture, a good hypothesis, and some examples. The rest is up to you, believe it if you will. Ignore it if you don’t, but every day science provides more evidence.
Primordial Earth was not like today. Not even close. Imagine a world that was void and dark…oh wait that is someone else’s story. The Earth was a mass of hot lava and pools of sulfur, hydrogen was plentiful, and there was some helium, and water. No water we would want to drink. Our solar system was still in turmoil, with meteors crashing into the planets. In fact there was no moon yet. Just a hot mass. The earth was cooling though, and stagnant pools of toxic sulfur water lay all around. Nothing was alive here, yet. For millions of years it was this way. Volcano’s erupted and the earth changed and reformed. Tons of meteors hit the planet. Carrying with them more water. The Earth was spinning fast through the universe on its orbit. At some point a meteor impacted the planet and the moon was split off. This was before we had our modern atmosphere. So the Earth aged and cooled, slowed down, and was mostly water. And then it happened,Life. Now scientists have found nucleotide bases in meteorites. Nucleotide bases are part of your DNA. They have also replicated in strict lab settings, what primordial earth would have been like. Out of that they created amino acids. The substance needed to make protein. In fact they were able to show how it could split easily. Life that would have come first here on earth was not complex. I would have to be simple, and we know that because of the fossil record. So the likely hood of DNA being present is small. What scientists believe existed was a form of RNA or TNA. Both are very basic compared to the complex structure of DNA. There was no Oxygen on Earth. Scientists believe, and the first life was anaerobic, and used sulfur. This type of bacteria does not need air, but produces it as a bi-product.
The fossil record, the makings of a living world came next. We begin finding simple life. Now any single celled organisms were soft and left no trace of being here, but what we do find is suddenly oxygen was here. The world went from being a lifeless blob, to having very simple life. Some of the first sea creatures found are very simple. One of the first plant/animal lives that has been found is Charnia. An odd non complex creature who used repeating as a method of growing. What this means is every part of it was a replica of the next. It had no variation in structure. Equally each of the specimens found looks like the next. Next we move to Arthropods called trilobites (we have found 50,000 species) and then it seems everyone wanted a shell. Monstrous fish begin to appear in the fossil record. Ones with big teeth, or pincer’s. Ones that had many legs and fins. Ones that had many many fins. Huge horrible looking things. Evolution seemed to take off like a shot, developing many new forms of life as it went. It was called the Cambrian explosion. During this period we find thousands of species. Variations so great the modern day world pales in comparison.
Soon we find fish like Megolodon. He made a great white shark look like a snack, along with other giant sea creatures. Plants became more varied, and so did the species living under the sea. The fossil record shows life was over abundant. By this time the Earth had a moon, and pretty much the orbit we do now, though the tilt was a bit different, and the polar caps were located in other areas. Everything was going along fine, and then, nothing. Something wiped out almost all life on earth, and life had to take off again. Whatever the catastrophe, it was cataclysmic, killing on a world wide basis, and scientists suspect it was a global freeze. The world went back to bacteria.
Evolution took off anew and tetra pods formed. This means four legged animals. The fossil record shows we went from amniotes, to vertebrates, to mammals. Scientists now believe that it was the velvet worm’s ancestor who first made its way onto land. The velvet worm has tiny holes in the side of its legs for breathing air. After vertebrates is where mammals split off from dinosaurs, Both existed during this era, but separate. Dinosaurs dominated the Mesozoic. Primitive plants lived on the surface of the land. Ferns, and small shrubs, and trees, nothing like today. This was to become food for animals on land for the next two hundred million years. Dinosaurs fed on these and the trees that were present in the Mesozoic. It was a hot period, and oxygen was plentiful. The earth was a warm biosphere. A virtual paradise for the evolution of dinosaurs, and the extreme evolution they underwent.
From fish to four legged creatures, we began the slow walk through time. After the extinction of dinosaurs, mammals took off. We became the dominating kingdom. Slowly primates evolved from simpler mammals. At some point a common ancestor to the chimp diverged and a few humanoid species were born. First Australopithecus Africana, then Homo Erectus, Then Neanderthals, and than Homo sapiens. On an island another species of hobbit like humanoids also evolved. They share a humanoid ancestor who evolved to the environment of the island. They were cannibals, due to the lack of food sources on the island. This is most likely the reason they died out.
Now evolution has always had a helping hand. That is mutation, speciation, and gene flow. Mutation means a small change has happened somewhere in the DNA. Now that mutation does not always benefit the species and it does not survive. That is a part of natural selection at play. If the environment does not suit the mutation then the variation will not live long enough to reproduce. This means it will die out before it can populate. Other times it is just what the species needs to thrive. This can mean a longer beak, longer legs, and in humans becoming erect, and growing bigger brains, loosing body hair, and eventually verbal communications.
Speciation means over time as two similar mammals begin moving in two directions, they often get more and more distant from each other due to environmental factors. Even while living in the same area. This can be due to high amounts of competition. As they get more distant it becomes harder and harder to interbreed, until finally, due to biological changes, the two can no longer interbreed, and are separate.
Gene flow is a species migrating from one place to the other, spreading out as it goes. As the genes flow from one place to the next, a new environment might mean some slight changes, and result in a new species. This has occurred in flowers, plants, trees, and numerous species that spread over the planet. Dust storms, hurricanes, and birds have helped to bring life to isolated islands. Over time the plants which adapted on islands became some of the most unique on earth.
It is through subtle changes that humans evolved. We currently have six thousand fossils of human evolution. Not to mention a complete fossil record of horse evolution. We have dinosaur fossils that lead us to modern birds including feathers. We have plants and microbes found in glaciers. The amount of evidence for evolution is astounding. We may not know what sparked the first life, but since then, there has been a long trail of fossils leading to modern-day. As we learn more we find how close and yet far we are from those creatures of the past. After all DNA holds the whole story. In four letters it spells out the code for a long line of change, and while we may lose a few genes off our switches, we still hold an entire history wound tight in a code that takes up ten books. One tiny strand that tells so much about the history of the whole planet.