. . . about 4 to 3.8 billion years ago, a dry, rocky planet began to undergo what scientists refer to as the "Great Bombardment." During this time, the presiding theory is that a gravitational surge caused by the orbital interaction of Jupiter and Saturn sent Neptune careening into the ring of comets in the outer Solar System. The disrupted comets were sent in all directions and collided with the planets. These water-rich objects may have provided much of the water in the Earth's oceans today.
It is speculated that about this time, a great deal of the water in the earth's atmosphere existed in the form of steam. Due to all of the volcanic activity, a great deal of soot also wafted amongst the convection currents, and as these molecules provided the seeds for clouds to form, torrential downpours began to fill the great basins we now know as oceans.
This led to the first life on earth, the ancestors of modern bacteria. Evidence suggests this occurred roughly 3.5 billion years ago. This bacteria's novel innovation was the ability to take energy from the sun and use it to fuel the processes necessary to support life! Suddenly, the planet's water supply was being used to power these cyanobacteria - living, "breathing" power stations - releasing an important byproduct into the atmosphere: oxygen.
This oxygen bonded with the iron dissolved in the oceans creating iron oxide, imbuing the waters with a deep reddish hue. This iron oxide settled on the oceanic crust, and over time various layers of sedimentary rock called iron formations piled up one over the other. About 2.4 billion years ago, all the iron (the limiting reactant) in the oceans had been used up for this reaction, and the cyanobacteria-released oxygen was able to saturate the atmosphere.
Our best understanding of the following timeline points to a global glaciation event which stifled much of life's progress. What energy made it through the earth's magnetic field could only help sustain life in areas that had no ice, or where the freeze was thin enough to permit light rays through.
While we are not quite shure what exactly brought about the end to snowball earth, scientists speculate that increased volcanic activity played a crucial role. About 545 million years ago, the Cambrian explosion introduced exponential growth in biodiversity. The fossil evidence shows a boom in single-celled lifeforms as well as soft-bodied multicellular orgnanisms, but perhaps the most familiar form of life with its roots buried here would be trilobytes and similar shelled sea-life.
Because certain types of organisms were more likely than others to become fossilized, and the conditons for fossilization to occur were not stable, the fossil record is not quiet complete from this time period. However, the ensuing eras documented a great deal of biological evolution, with branches and branches spurred off of the evolutionary tree.
Over this time various mass extinction events occurred, razing the evolutionary playing field and creating openings for new life forms to sprout. Of these events, the first was the Ordovician-Silurian event about 450-440 million years ago. The causes of these events are debated by scientists, but the leading theories claim climate change, volcanic activity, and meterological bombardment.
While life was running through its own performance on planet earth, the stage was undergoing its own renovations. The continents as we know them were dynamic playgrounds for plate tectonics, a phenomenon which is constituted by seafloor spreading and subduction, the two forces acting on the oceanic and continental crusts. Because of this, parts of land now were underwater millions of years ago, and vice verse. The continents moved - on average a few centimeters per year - and as they did, they would divide and collide with each other. At their boundaries mountain ranges formed as one plate slid underneath the other, lifting it higher.
The contents went through this process of conglomeration and division numerous times, but the most recent instance of their complete conjoining is the supercontinent Pangaea which formed roughly 270 million years ago, losing for 70 million years before it broke apart. At this time the oceans were all one, large ocean - named Panthalassa - which covered about two thirds of the planet’s surface. This all occurred during the Permian and Triassic periods, which saw the Permian mass extinction wipe out over 95% of the species on the planet 248 million years ago.
When the Pleistocene epoch began 2.6 million years ago, several-mile thick ice sheets sprouted in the northern hemisphere, advancing during glacial periods and retreating during the warmer interglacial periods - such as the one we find ourselves in now. Our current interglacial period is called the Holocene, and it started about 11,500 years ago. The recurrent ice ages help explain the process of global warming as a sinusoidal wave function, a process where the planet heats up and cools down cyclically. Enter: humans.
As a species, we have surpassed all other forms of life in our ability to change the environment. No other species has been able to alter the planet’s atmosphere as much as we have in such a short period of time. The preservation of our ecosystems is a matter that we must address, because though the planet may reset itself under certain conditions, this would take place on a timeline that we, as a species, may not be around to see.
As you can see, the planet has a rich history - one that set the stage for humanity's great performance - but will we be the great showmen who appreciate their theater and respect its integrity, or will we leave it a mess for the theater crew to fix.
By joining the Tangency Foundation on restoration projects, you can help preserve local ecosystems and take the time to appreciate the billions of years that brought them here.