If an alien had accidentally visited Earth only 600 million years ago, without a microscope, it would have been difficult to conclude that there is life on it. How the biological Big Bang then happened.
It is not easy to be an organism on Earth. As far as we know, being an organism somewhere else is not such a common occurrence at all. And being human is even harder. About 90% of the living space in the world is practically completely inaccessible to us. We cannot breathe in water, and it is difficult for us to do that at altitudes of over 3500 meters above sea level. To understand how we even managed to get to this stage, we have to go back about 600 million years to the past, when the overture of a magnificent event that can be compared in the context of biology and life science to what the Big Bang is in physical sense – and that is the biological Big Bang known as the Cambrian “explosion”.
Life on Earth, according to modern molecular fossils, originated 3.8 billion years ago. That was the period that followed the end of the so-called epoch. the late bombing in which the Earth collided with objects such as asteroids and comets today – only then they were much larger and more numerous – which arose as a kind of scrap from the formation of the known planets of the solar system. Somewhere, about 3.8 billion years ago, more or less stable conditions were created for the emergence of the first single-celled life forms.
Earth like a snowball
He spent almost 6/7 of his history in the form of the single-celled simplest form of life. Before that, there were only bacteria and some types of archaea. So, if the alien had visited the Earth during that period, if he did not have a microscope, he would not have been able to conclude that the Earth is inhabited. He could assume that only on the basis of the impact that these simple organisms had on the environment, primarily because they were responsible for the appearance of oxygen in the atmosphere. Although these are anaerobic organisms (organisms that live in conditions without free oxygen), they were in charge of creating the first algae, the so-called plankton, which formed the additional amount of oxygen necessary for the formation of all later forms of organisms (plants, animals and similar things). But why didn’t plants, animals and similar things appear for so long?
In the distant past, events of such a dramatic nature — changes in the physical nature of the Earth — took place that they somehow dictated a path that led to more complex life forms. The last, most significant of these events, was the global freeze that occurred 600 million years ago, and is popularly called Snowball Earth. At that time, the whole Earth was covered with ice, the oceans were under an ice crust almost one kilometer thick, which was a completely catastrophic moment for all forms of life. At that time, the average temperature of the Earth in the tropics was -20 ° C, while at longitude and latitude 20/44 it was on average about -50, -60 ° C. In such conditions, the only place where our ancestors, the simplest organisms, could survive were the areas immediately around the geysers and volcanoes. When the Earth cools completely and when a sufficient amount of snow and ice is formed, it looks white when viewed from space, which means that its coefficient of reflection is much higher than usual, so that it reflects much more sunlight and heat. In this way, the Earth tends to continue to cool until it reaches a sufficiently low temperature that leads to general icing.
The only way out of this situation was provided by volcanoes, geysers and hydrothermal springs under the ocean because they gradually pumped greenhouse gases (carbon dioxide, methane, sulfur dioxide) into the atmosphere. It is a moment in the history of life in which this effect was necessary for its further development, since it led to global warming. This process took about a million years, as long as it took to melt the ice that surrounded the Earth. This era ended around 575 million years BC.