Source: Adam Grossman / Nick Risinger – Observe the small blue dot on the right. This is how far humanity’s radio signals have traveled through interstellar space – about 200 light years in diameter. Any alien civilizations outside this blue dot are unaware of our existence. This is why intelligent life would be hard to find. Even if there were thousands of alien civilizations scattered throughout the Milky Way, we’d have trouble making contact due to the vast size of the Milky Way.
Throughout history, as we’ve gathered more information about outer space and the universe, questions have arisen about whether life – especially intelligent life – exists out there in the universe. While Earth is the only known planet to harbor life, we still haven’t ruled out the possibility of life within our own Solar System.
There are billions of galaxies, with each galaxy having billions of stars. This means that many stars like our Sun exist with planets in their habitable zones. The habitable zone is a certain distance from a star where a planet has temperate conditions, to the point where life can arise.
Current hypothesis of the presence of life in the universe
Many scientists have concluded the following:
- Simple, single-celled life is common throughout the universe.
- Multicellular life is more rare than single-celled life.
- Intelligent, radio-communicating life is exceptionally rare.
Now, how could this possibly be the case? All three points will be discussed, but this article will elaborate more on the third claim about intelligent life.
Single-celled life
Many scientists conclude that single-celled life is common throughout the universe. This is because Earth is used as an example. Earth formed over 4 billion years ago, as a very hot large rock in space. However, shortly after it cooled down, life formed quickly as soon as the conditions allowed. Once Earth cooled down, and water formed, then came life.
It’s 100% guaranteed that life arose 3.5 billion years ago, however, many think that it formed even before that, around 4 billion years ago, or in other words, just 500 million years after the planet formed.
So, even if there was a one in one billion chance of life arising per year after Earth’s formation, it will almost certainly form after one billion years.
Astronomers and space agencies around the world are conducting missions to various Solar System bodies like Mars, and some of Jupiter and Saturn’s moons to check if these planets possibly contain any living matter.
If single-celled life were found on any of these planets or moons, it could indicate that single-celled life is very common, especially since Mars, and some moons in the Solar System are far less habitable than Earth.
Multicellular life
Multicellular life first formed 600 million years ago. Dozens of millions of years after that, the Cambrian explosion happened. While the Cambrian explosion wasn’t literally an explosion, it was a period of rapid evolution. In just as little as ten million years, life on Earth went from being very simple to complex – to the point that it resembled most sea creatures we observe today.
However, this rapid evolution took place in the ocean. The first land animal still took another 100 million years to evolve.
The cause of the Cambrian explosion is still a mystery. Scientists think that a rapid increase in oxygen caused it.
However, the Cambrian explosion might’ve not been that rare. Countless organisms existed, and Earth’s conditions were changing. Given enough time, an event like the Cambrian explosion could’ve been inevitable.
Intelligent life
Let’s assess two meanings of intelligent life:
- Conscious, self-aware life that can communicate and use tools.
- A highly intelligent civilization that can communicate via radio.
Both can be rare, but it might be obvious that number two is far more rare than number one.
The first one can be rare because if we examine Earth’s history, several things had to precisely happen for humans to exist. Here are a few examples:
1. The Chicxulub impact event
The Chicxulub impact was the event that wiped out the dinosaurs. Dinosaurs were apex predators, and there was a minimal chance humans would survive and thrive if numerous dinosaurs were present.
A 6.2-mile-wide asteroid struck Earth and wiped out nearly all species on Earth. Only a few species survived the impact. The asteroid also had to strike at an ideal angle of 60 degrees to properly kill off all the dinosaurs. Had it struck at a lower angle, the devastation wouldn’t be as bad, and the dinosaurs could’ve survived – possibly until the modern day.
Even if they survived the impact and died several million years later, this alternate history could’ve sparked a chain reaction that would’ve drastically altered future life on Earth. This is known as the butterfly effect.
2. The proper conditions for evolution.
Numerous conditions had to be met for humans to be self-aware, and intelligent enough to use tools. However, we will discuss a few of them.
Bipedalism is necessary to free the hands
Bipedalism is when a species can walk on two legs. Bipedalism has allowed humans to freely use their hands for tasks unrelated to walking, like using tools.
Fingers
Fingers are needed to grab and make use of tools.
Ability to run long distances
Although this didn’t directly cause intelligence to arise, it contributed to several other factors that did.
Hunting animals over long distances
Early humans were successful in hunting animals, despite animals being faster. Early humans would run at a steady pace after a prey, while the prey would exhaust most of its energy from sprinting. After a long distance, the prey is too tired to run, and the humans catch up thanks to their consistent, low-intensity run after the prey.
Access to nutrient-rich foods like meat
Catching prey allowed humans to eat nutrient-rich foods, which helped brain growth. Brain growth is crucial for intelligence.
These 5 factors were a few of the many more necessary factors for humans to become intelligent.
This can lower the probability of intelligent life arising. Had any one of those factors been different, humans would’ve never become intelligent, or even could’ve gone extinct.
Rise to intelligence
The definition of intelligent life we will use is a civilization capable of radio communications because that is humanity’s only hope of discovering extraterrestrial life.
Humanity started using radio communication in the early 20th century. Since then, the first radio broadcast has been traveling through interstellar space at the speed of light. Check the picture above again to see how far it has traveled.
Just like the rise of a candidate for intelligent life, the actual milestone of achieving radio communications depended on a lot of strict factors. We won’t be discussing all of them, but just enough to reveal how unlikely it was to make it to the early 20th century.
Natural disasters
Although most natural disasters aren’t an existential threat, there are a few. Throughout history, supervolcanoes have caused global winters that can kill off the majority of a planet’s species.
Although not verified, the Toba Eruption 74,000 years ago left a bad mark on humanity. Ash from the supervolcano blocked off the Sun for six years. Once again, the Toba Eruption was confirmed as an actual incident. The only debate was how well humanity adapted. Did it almost wipe out humanity or were only a few groups affected?
That should still show you the idea of how a supervolcano can cause mass devastation. Imagine it happened earlier when there were fewer people.
Societal factors
We will discuss multiple smaller factors, as most will relate to human society in General.
- Use of tools
The usage of tools was necessary for humans to have an ordered civilization. Evolutionary factors like bipedalism and fingers have helped humanity adapt to using tools.
The efficiency of tools was likely accidentally discovered. Tribes throughout the world realized sharp objects could pierce things better. This helped them realize it was easier to hunt animals this way.
The same can apply to other tools when it comes to digging or mining. Early humans realized it was easier to conduct operations with certain tools.
- Permanent settlements
A permanent settlement was crucial for a society to develop. Many tribes were unlucky, since numerous environments were inhospitable for a permanent settlement. This meant that many tribes remained as hunter-gatherers until they died off.
The first hunter-gatherers to develop into a permanent settlement were lucky that the environment they were in was abundant with resources, and had hospitable conditions.
- Agriculture
Agriculture was necessary for permanent settlements to thrive. Many tribes could’ve established a settlement but quickly died off due to the lack of agricultural practices.
The first successful permanent settlement likely had to accidentally discover agriculture, which helped make food abundant.
What does any of this have to do with extraterrestrial intelligent life
As mentioned earlier, these specific circumstances had to be met. This means that out of all possible planets with life, many have failed a certain trial which prevented the development of Intelligent life.
For example, many planets with living matter might never have a Cambrian explosion. Or some might have a dominant species that could prevent an intelligent species from existing. Or if some intelligent species do arrive, they might go extinct due to a failure in a single trial mentioned above.
This concludes that a species with a human-like society could be very rare.
Sources
https://news.stanford.edu/stories/2024/07/revisiting-the-cambrian-explosion-s-spark
https://evolution.berkeley.edu/the-cambrian-explosion/