One of the most frequently asked questions in any scientific, philosophical, or theological debate is – where did life on Earth come from? Scientists already know a great deal about how life on Earth came to be as it is today. There’s physical evidence all around showing how life has evolved and changed over the millennia of Earth’s existence.
We know much less about the first life on Earth. So what was the first living thing from which all other life on Earth originates, and how did it come to be alive?
What Is Panspermia Theory?
Panspermia is the theory that life on Earth originated on another planet altogether and was deposited on Earth due to a meteor impact. If this sounds unreasonable, like something out of a superhero comic book, that’s understandable. However, science has long laughed off this possibility as a stretch at best.
However, recent scientific advances in understanding what “life” actually means have revived the debate about the Panspermia theory. There’s still a long way to go before this theory will be considered scientifically likely. But it appears that the possibility of organisms on Earth have originated on other planets holds more water than you may think.
The Birth Of Our Solar System
The planet we know today as Earth wasn’t always the same as it is today. Yes, there was Pangaea, and the dinosaurs, and single-celled organisms in the ocean. But before that, Earth was just a hot, dead rock in space continuously blasted with cosmic debris.
If we go back just a little bit further, it wasn’t even a solid rock. Our entire solar system was just a giant, swirling dust cloud. Scientists are still far from certain what happened, but something disturbed the dust cloud enough to make it start to pull together.
The pulling together of dust on a cosmic scale caused it to swirl so quickly that it began to generate its own gravity. As a result, hydrogen protons fused, producing helium and releasing massive amounts of energy that would eventually become our Sun. That was 4.6 billion years ago.
Over the next 100 million years, all the matter in the solar system that wasn’t consumed in the formation of the Sun kept swirling. Over time, it collected into the larger and larger masses that eventually became Earth and the other planets of our solar system.
Conditions For Life
Even then, though, Earth was just a hot rock hurtling through space around the Sun under constant meteor bombardment. The hot magma that made up Earth’s surface began to cool and sink, forming the molten core and the oceans. Then a massive meteor impact around 4.5 billion years ago formed our Moon, beginning Earth’s journey toward habitability.
Scientists now believe that Mars, on the other hand, was once more habitable than Earth in its pre-Moon days. So while science has yet to definitively prove the current or former existence of native Martian life, we do know that the right conditions for life may once have existed there.
Early Life On Earth
Meanwhile, life appeared and evolved so rapidly on Earth that scientists are still trying to figure out how it happened. We don’t yet know when or how life on Earth began. But we know that there are signs of life on Earth 3.8 billion years ago and definitive proof of life as early as 3.5 billion years ago.
What’s fascinating is that the building blocks of this early life on Earth are the same ones that make up all known life today – DNA and RNA. So some scientists today believe that the rapid appearance of these molecules on Earth can mean one of two things.
First, it could mean that life on Earth evolved more rapidly in the early years than it has across recorded time. However, the alternate theory is that life on Earth had such a complex molecular structure because it had already evolved elsewhere – on another planet.
We’re not talking about Superman arriving from Krypton in a small spaceship. Instead, the Panspermia theory posits that a meteor blast from a nearby planet may have launched space debris into Earth’s atmosphere. This debris, some scientists believe, may have carried with it microscopic life forms that, against all odds, survived and thrived on Earth.
The most likely origin for pre-evolved life forms is Mars, which is now believed to have previously been habitable. According to the Panspermia theory, Mars was not only habitable but sustained life during a period that overlapped with Earth’s early days of habitability.
If a meteor struck Mars with enough force, such as the force of the meteor that struck Earth forming the Moon, it might have caused Martian debris to fly into space. Martian microorganisms living in that space debris may have survived the journey, landing on Earth and taking root on its newly habitable surface.
Could Panspermia Theory Be True?
It may seem a little far-fetched to think that a space rock hitting the surface of Mars could send Martian life hurtling toward Earth. However, the minimum distance between Mars and Earth, even when their orbits are nearest, is 33.9 million miles. So is it possible for Martian space debris to travel that far?
Earth’s surface is littered with craters from massive meteor impacts. Around 2.2 billion years ago, a meteor larger than South Africa’s Table Mountain collided with Earth, leaving an impact crater that scientists believe was once over 185 miles across. And 65 million years ago, Earth was struck by a massive meteor that wiped out the dinosaurs and left a crater 150 miles wide.
That kind of cosmic impact is almost impossible to fathom, as we have no natural frame of reference to compare that amount of force to. But we do know that Martian planetary material has been found on Earth’s surface. So not only could it happen – it has happened.
Could an organism survive the journey?
Even if a blob of planetary material carrying a Martian microorganism could make its way from Mars to Earth, how could that tiny creature survive the extreme journey? It seems implausible between the vacuum of space, the solar radiation, and the force and heat of the impact itself.
However, there are already organisms on Earth that have proven themselves capable of surviving these extremes. For example, tardigrades, sometimes called “water bears,” are tiny eight-legged micro animals that can survive at temperatures from absolute zero to boiling, under six times the pressure of the deepest ocean, and in the vacuum of space.
They can also dehydrate themselves and go dormant indefinitely, a process called cryptobiosis. They do this to survive excessively dry climates, and when conditions improve, they rehydrate themselves and go on as though nothing happened.
Even simpler organisms like bacteria could survive all extreme conditions and live inside a rock for years. Scientists believe that a one-millimeter colony of bacteria could survive unsupported in space for up to eight years. So we already know of life on Earth capable of surviving an unprotected journey on a rock from Mars. We just haven’t proven that it’s happened.
Potential Alien Animals
Aside from the fact that Martian life could have hitched a slingshot ride on a rock hurtling toward Earth, some scientists believe they’ve found proof of those alien origins. Cephalopods, particularly the octopus, feature traits and adaptations that appear out of nowhere on the evolutionary timeline.
Instantaneous camouflage, camera-like eyes, physical flexibility, and complex intelligence all evolved in cephalopods in a way that scientists haven’t found in any other life form. In addition, the octopus genome is staggeringly complex, with 33,000 more protein-coding genes than humans.
One scientist described the octopus genome as so complex that it could have “futuristic” origins. Some argue that Panspermia is one possible explanation for such an advanced state of evolution. Specifically, some scientists believe it’s possible that cephalopods evolved on some other planet and arrived on Earth as cryopreserved eggs.
Diversity Of Life On Earth
Now, evolution is a complex process that science is still trying to understand. Just because other species haven’t developed the same evolutionary advantages as the octopus doesn’t necessarily mean those advantages have alien origins.
But our planet is covered in diverse plant and animal life, and scientists are still discovering strange and unfathomable creatures in Earth’s oceans. Without a clear evolutionary bread crumb trail to explain them, scientists can’t rule out the possibility of alien origins.
There’s also the fact that DNA and RNA – the building blocks of life as we currently know it – are rather unlikely candidates for survival on Earth, at least at the time when life on Earth began. Water is highly corrosive to both DNA and RNA, and yet Earth was covered entirely in the stuff in its early habitable days.
Yes, science is already pretty confident that life on Earth began in Earth’s oceans. But why would DNA and RNA become the basis for every genome on a planet covered in a substance that dissolves them? The possibility seems counter to any theory of natural selection.
Life is complex and fragile, yet it became incredibly tenacious on a just barely hospitable planet in a couple hundred million years. While not anywhere near conclusive, the miraculousness of it all is enough to consider at least the possibility that life had a head start elsewhere.
The Problem Of Proof
As with any theory on the origins of life on Earth, proving it is next to impossible because there were no eyewitnesses to the event. Scientists must rely on physical evidence that they’ve found on Earth and other planets to determine what happened.
If life on Earth did originate on another planet, what kind of proof would we expect to find, and where would we hope to find it? Current and future expeditions may uncover evidence of DNA- and RNA-based life on other planets, such as Mars.
Given the complexity of DNA and RNA, the likelihood of evolving independently on two relatively nearby planets is incredibly low without some form of Panspermia. Finding similar life forms on two separate planets would be strong evidence that those life forms have the same planetary origin.
But even finding life on Mars wouldn’t be the end of the conversation. Humans on Earth have been sending machines into space for over half a century now. So if microbes can survive the journey from Mars to Earth inside a frozen rock, they can certainly survive a trip in the opposite direction, well protected inside a space-faring machine.
In which case, we may have artificially seeded other planets with life unintentionally. Whether that life actually survives and takes hold is a question of habitability and luck. But any signs of life found on Mars could be there due to unintentional contamination from Earth.
Needle In A Haystack
On the other hand, even if we never find signs of life on Mars, that wouldn’t necessarily disprove the Panspermia theory. Mars is a large planet that we still know relatively little about. Its landscape is still largely foreign, and potential life or signs of it could be hiding anywhere.
Short of scouring every inch of the planet’s surface, it would be impossible to conclusively say that there are no signs of life on Mars – only that none have been found that scientists can identify.
There’s no reason life on Earth had to originate on Mars, either. It could have come from anywhere, within the solar system, or anywhere in the galaxy. It’s even possible that life from one planet seeded multiple other planets or that multiple planets seeded one.
With our currently available science, conclusively proving or disproving Panspermia is unlikely to happen any time soon. But the Panspermia theory, if true, has astounding implications. If life can be seeded from one planet to another, life may be much more common in the universe than we ever could have imagined.