Is Earth really benevolent to life? (pub October 25, 2024)
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Every day I feel better in condition, I think I will barely be in time for the half-marathon next month, this week I ran 10 km on Wednesday and 12 km today.
The good thing about running longer is that you wander more and have more mental discussions, some of which are very interesting. That was the case today, I had barely gone 2 km when an early gray heron flew over me, and the sun had not yet risen. I said good morning and the question appeared in my mind, is Earth really benevolent to life?
It would seem like an absurd question, I'm asking myself while I'm exercising, I've just seen a spectacular bird, and I'm living in one of the moments of greatest biological diversity in the history of the Earth, not the greatest, but very close.
But let's think, how many mass extinctions have there been in the history of the Earth? The immediate answer would be: five. But no, those are the largest that have left their mark on the fossil record, but there were several before.
Let's start with the great oxidation associated with the appearance of photosynthesis, about 2.8 billion years ago the first cyanobacteria appeared that carried out photosynthesis, producing Oxygen, which did not exist in free form on Earth. Oxygen, living up to its name, began to oxidize what it found, so at first it did not accumulate in the oceans, but the time came when it began to accumulate and with it the first mass extinction occurred, oxygen was toxic to all primitive organisms. Obviously, among the organisms that became extinct were many photosynthesizing cyanophytes, so oxygen production practically stopped, and the concentration of oxygen, being very reactive, decreased rapidly. This allowed the surviving organisms to begin to reproduce, including photosynthesizing cyanobacteria, so oxygen began to accumulate again, causing another mass extinction. This cycle must have been repeated several times until the species that had survived the extinctions, taking advantage of characteristics that allowed them to do so, began to predominate, including photosynthesizing cyanobacteria. How many mass extinctions occurred in this process? Who knows, but there must have been several.
But then comes another important change, the earth literally froze. This freezing began about 700 million years ago. What caused it? I blame it on oxygen, which altered the atmosphere to such a degree that its greenhouse effect almost disappeared. So here that must have caused the disappearance of a large number of species.
AND THE CAMBRIAN ARRIVED
Just like if nothing happened?
The Cambrian is a surprising period, and, yes, it is difficult to measure its biological importance. All living organisms currently have an ancestor that already lived in the Cambrian. But it did not appear out of nowhere, before there was the Ediacara fauna.
The main difference between the organisms of the Ediacaran fauna and the Cambrians is that the former did not have rigid structures, so their fossilization was much less likely, but with what is being learned it was very diverse. We already know that the first mobile animals come from then.
But the Ediacaran fauna disappeared about 540 million years ago and then the Cambrian arrived, so another mass extinction, which is not counted in the five largest.
And then come the 5 biggest ones that everyone thinks about. Those that have left a clear record in the fossil record
1. Extinction at the end of the Ordovician, about 400 million years ago, approximately 85% of species disappear.
2. End Devonian extinction, about 370-360 million years ago. About 75% of the species,
3. Extinction at the end of the Permian, and end of the Paleozoic. THE GREAT DEATH. About 250 million years ago. It is the largest extinction recorded in Earth's history, approximately 96% of marine species and 70% of terrestrial species.
4. Extinction at the end of the Triassic. About 210 million ago. Approximately 80% of species disappeared
5. Extinction at the end of the Cretaceous, end of the Mesozoic, and goodbye to the Dinosaurs, among others. 66 million years ago, approximately 75% of species.
But even those are not all, among them there are some that did not become so important at a global level, but regionally they caused many changes.
Currently, we are going through a new, caused by human beings, of sapiens We only have the name of the species.
The earth, at times, is benevolent, at times the opposite.
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