It was on a planet not very far from a very calm star. The planet had an orbiting body. At first it seemed to be a very boring world. There were barely any events. Aside from the greater amounts of uranium at its core and being more dense than the average planet it did not seem very intriguing to this cosmic giant. But then he saw it for the first time. He came upon a shallow pond and there was movement. It was small but he was very careful not to disturb it. It was as if something had spoken life into this always motionless system that he had gotten so used to. At first there was one. And later it would become two. It was taking some of the loose molecules around it and making it part of itself. When it became two the other was like itself. This small lukewarm pool of ambrosia was very carefully documented by the observer. As he watched the two become many. They started having changes in the ways they are built, some would be faster and some longer, all seemingly trying to find a better way to consume and make part of themselves. They would start only using certain parts and expel the rest as waste. Others even formed and started specializing to start eating the waste.
It this continued and given enough time the lifeforms had found their way into all the major bodies of water on the planet. They kept becoming more and more , consuming all of the carbon dioxide and expelling the oxygen into the atmosphere. This continued as they even started changing the hues of the world. More and more. Trillions of them. Until some day there was a tipping point.
They had filled the atmosphere with so much oxygen that they could not survived. And billions started dying off at a rapid pace. The observer had a suspicion that this might be their end. But one day when the observer would look back at this moment it would serve as a reminder, that life will always strive to survive. Their numbers had dwindled and their vast population was but a fraction of its original glory.
In this bleak moment a new form of life had formed. one that would consume oxygen as its primary source and expel carbon dioxide into the atmosphere. This early atmosphere was now extremely oxygen rich, allowing the new life form to thrive. Their numbers would grow quickly and they would restore the necessary balance that would allow the two types of cellular life forms to co exist.
This balance was maintained for the better part of a few million years. In it the resources for many new forms of life would become the dead lifeforms, and even other still living lifeforms. Some cells would later find that it would be very beneficial to for clumps and survive in that manner. This would be the start of a new phenomena known as multi-cellular life. The cells optimize their survival by having different cells in the same body perform different purposes. It would start off small like the outer layer of cells becoming more durable so the inner cells could focus on metabolism. Then there would be other cells that would move inside the walls of the larger cellular cluster and eat what was not part of the cluster . Becoming the earliest forms of immune systems. Larger and larger lifeforms formed and they started branching in different directions. There were still two main branches, oxygen consuming and carbon dioxide consuming life.
The sea floor which was previously lava and was very porous. The sea would in the coming 200 million years sypher through the floor and waterlog a lot of the landmass. This resulted in a lower sea floor. And would give rise to some islands, which would later as the sea floor lowered become the first continents. The life on the shallow waters would be exposed to more air and would thrive there. And as the water level kept lowering there remained some life on the rocks. These were some of the first species of fungi. They had the ability to degrade the rock and slowly feed off of it.
As the continents became larger and larger fungi would fill them making all a lot of the surface into a finer grain , becoming the ground that would serve as foundation for the first plant-life. The observer saw that the multicellular plant-life that was in the ocean had found a way to sink roots deep into the ground that the fungi had created, they would live off of the carbon dioxide in the atmosphere and rely on nutrients such as phosphorus, nitrogen and other metals that it would bind to the carbon to form fractal like structures. They were also using the stars radiation as a supplementary energy source. This new form of land plant-life quickly became one of the fastest growing species. And they remained that way for millions of years.
This lifeform did have one slight problem. The carbon structures that they formed as their bodies would begin to fill the planet as they died. They merely continued growing on the dead . Seemingly nothing able to consume their strong protective hides. Their dead would pile up in valleys and in some places they would stack up hundreds of meters high. Barely leaving any space for the large fungi to grow. Their sheer weight compacting all others . This continued for far too long, it was only after millions of years that some micro organisms evolved to be able to break down these dead trees. With these new organisms the forest floor changed into something new entirely.
Whilst all this was happening life in the ocean had taken a very different turn. There were many species using the water as a medium of movement. And using the oxygen and other life forms as forms of sustenance . Three main interesting lifeforms started thriving, Molluscs, Chordates and Arthropods. Molluscs were using the excess calcium in the ocean floor to form hard shells round their bodies for protection . Chordates were using it inside of their bodies to for bone like structures. This would serve as a frame on which their muscles would be fixed. And Arthropods used the calcium on the outside to serve as a best of both worlds solution, still having different joints and muscles fixed to these exoskeletons, but they had less range of motion than the Chordates had.
All of the major lifeforms that became very successful had a central nervous system. They developed this to be able to give commands for the large cellular clusters. Using an array of chemicals to pulse chemical signals. This would be used for movement in order to obtain food, and also to escape. Many of the lifeforms would also form sensory organs that would serve as input of information for their central nervous system. These being things like touch sensors, light sensors and chemical sensors. All of this input would be processed and an appropriate output would be formulated. The place where they were processed would become more advanced as the life forms evolved. Being able to retain information about the inputs they received and formulating responses, the more a response was formed with success the better they became at responding to the needed situations, as the inputs became more, the outputs became more and this core became bigger and bigger.
by the time trees had finally formed on land there had long since been fish in the sea. And when the trees finally occupied a large part of the land the Arthropods were the first to reside on land. Because there were so many trees and the atmosphere was warm and humid, they who had no lungs and were breathing in through their exoskeleton were very much successful on land. They quickly multiplied and became plenty forming their very own ecosystem on land.
The Arthropods were thriving on land, and the Chordates inn shallower waters were taking notice. Note that the sea had now long been in the world and many Molluscs had died in the waters, their shells were eroded and the same was true for small rocks. this formed many beaches. The Chordates, seeing the plentiful food would start to venture on land in short doses. Some starting to lay their eggs there in the higher oxygen environment, and because it seemed safer. Their ventures with time became longer and longer. Their gills later evolving into lungs to take full advantage of the rich oxygen environment. Many would begin to move inland and completely abandon the waters.
This would become the beginning of terrestrial life on this world. The observes was enjoying all of the new things that were shown to him. He was struggling to keep up with the intricacies of the ever evolving ever diversifying beings in front of him. He had come to love this planet. Wondering what it would be like to live like these beings. Even learning from their way of retaining and responding to information. Ways he might begin to implement upon himself. He had seen that being under threat of malnourishment and predators had served as inspiration for many divine evolutions.