Thursday, January 5, 2023
The Universe is nearly 14 billion years old.
Earth formed about 4.54 billion years ago. It may have been struck by “Thea,” a planet the size of Mars, 4.5 billion years ago, forming the moon (and possibly supplying much of Earth’s water).
The planet was mostly molten until 4 billion years ago when the continental crust began forming.
Prokaryote life (cells with no nuclei) developed during this time, certainly by 3.5 billion years ago. Photosynthetic life may have appeared as early as 3.2 billion years ago. Life is almost as old as the earth itself.
By 2.3 billion years ago photosynthetic processes caused a large increase in the oxygen level in the atmosphere. A few 100 million years after that eukaryotes using more complex forms of photosynthesis appeared.
1 billion years ago, fungi may have been the first organisms to develop on land.
Single celled plants developed 700 million years ago. Multicellular life developed 580 million years ago. 538 million years ago came a major diversification in life forms known as the “Cambrian Explosion.” Most of the major groups of organisms we know today developed.
The first vertebrates arrived on land 380 million years ago. Dinosaurs and mammals developed roughly 250 million years ago.
Hominids, by contrast, have been around 2 million years at the most.
Roughly 5 billion species have lived on Earth at one time or another. 99% are now extinct.
What does this suggest?
1, The conditions on planets that support life can change drastically. Life lived on the earth for at least a billion years before there was much oxygen in the atmosphere. Several supercontinents formed and broke up during this time. The earth was practically a ball of ice at least 3 times. If humans ever visit a planet that supports life, it may be more or less hospitable depending on where in its life-cycle it is. The Earth could become less hospitable again too.
2. Types of life change. There is nothing on Earth like the dinosaurs anymore. There are a lot fewer of some types of animals than there used to be (megafauna), and a lot more of others. It is possible that a new form of cell besides the two we know might develop at some time in the future.
3. Humans have been around for a fraction of the time that life has existed, have been civilized an even smaller fraction, have less than 10,000 years of recorded history, and have only been capable of sending signals off planet for 200 years. If we ever find a planet with life on it, it is highly unlikely that it will be intelligent life. If you were to time travel randomly to some part of the past where life existed, you would have a 1 in 7 chance of encountering complex life, and a 1 in 1,750 chance to find the ancestors of intelligent humans.
So it seems that our chances of finding other intelligent life in the galaxy are minimal. However, this really only holds if we consider “intelligent life” to be a species with a level of intelligence and technology similar to our own.
We don’t know the average longevity of an intelligent species. Maybe they generally destroy themselves in one way or another soon aver developing industrial levels of technology. Maybe they continue to develop for thousands, hundreds of thousands, or millions of years. Or maybe they stagnate or stabilize at a certain level of technology that is all that can reasonably be obtained.
Only in the last case are we likely to ever encounter aliens with technology like our own. Otherwise we are likely to encounter intelligence and technology that is very primitive or unimaginably advanced.
It is possible that sapient species may generally develop to a technological level at which they can seriously harm their ecosystem and each other and then decline. This could happen over and over again on a life-supporting planet. Maybe every few million years a new species evolves to sapience, then eventually kills itself. This would increase the chances of us meeting a sapient race somewhere–it could be one in a series of several hundred stretching back millennia. Is it possible this has already happened on Earth? Did an intelligent reptile evolve in the last couple million years of the Mesozoic? Did industrial pollution, not an asteroid, kill the dinosaurs? Would we be able to detect a species that only had the capacity to leave their mark on the planet for the last 10,000 years of their existence if they lived 230 million years ago? It bears thinking about. Is there anything humans have created that could provide evidence of our presence 200 million years from now?
The efflorescence of technology has occurred in a vanishingly short period compared to the time non-microscopic life forms have been around. The Earth has billions of years left to exist. Unless we fuck it up, it probably won’t change much in the next million years. We can’t even imagine what human life will be like in 1000 years, never mind a million.
Black Hole Radiation 