The birth of life on Earth is one of the biggest puzzles scientists have ever faced, but there are theories that question even if it all started here. And it is that among the many theories there is one that is intriguing for some scientists, but very annoying for others. It’s called “Panspermia,” the theory that life first came to Earth from outer space. Not in spaceships, of course, but as passenger materials aboard meteorites.
The principle behind the panspermia theory is that life originated outside of Earth – that is, it is of extraterrestrial origin – and traveled to our planet, finding a hospitable climate in which to thrive and eventually evolve into life in the earth.
Cosmic seeding
It is an ancient concept, dating back to the concept of taxonomy, when the French historian Benoit de Maillet proposed that life on Earth was the result of germs “seeded” from outer space. Since then, scientists from Stephen Hawking to Sir Francis Crick (who abandoned his early support for the RNA world hypothesis) have believed that life on Earth originated outside of this planet.
The theory, as we say, comes from afar, but in recent times it has gained new support as astronomers have discovered just how full the universe is with organic compounds.
Although no evidence has yet been found to prove it, the idea of panspermia is not considered as far-fetched as it might initially sound.
Three fronts
The theory of panspermia falls into three broad categories:
1. Life traveled through space debris from somewhere outside our solar system, the concept of lithopanspermia
2. Life traveled from another planet in our solar system, which is known as ballistic panspermia or interplanetary panspermia.
3. Directed panspermia, which holds that life on our planet was purposely spread out by already established and intelligent life.
As the panspermia hypotheses advance, interplanetary panspermia is gaining wide acceptance in the scientific community. Chunks from other planets have long bombarded Earth in the form of meteorites. In fact, a meteorite, ALH84001, discovered in Antarctica in 1984, carries what some scientists consider the traces of life or the precursors of life as amino acids. It is estimated that it separated from Mars more than 4 billion years ago.
Panspermia: seeds everywhere
The word “Panspermia ” comes from the Greek and means “seeds everywhere”. The seeds, in this case, would not only be the building blocks of life, such as amino acids and monosaccharides, but also small Extremophilic organisms. The theory states that these “seeds” were scattered everywhere and that they most likely came from meteorite impacts. It has been proven through the remnants of meteorites and craters on Earth that the early Earth suffered countless meteor attacks due to the lack of an atmosphere that could weaken its entry.
Anaxagoras
This theory was first mentioned by the Greek philosopher Anaxagoras around 500 BC. The next mention of the idea that life came from outer space was not until the late 1700s that Benoit de Maillet described the “seeds” that rained into the oceans from the skies.
It wasn’t until well into the 19th century (in 1871 ) that the theory really began to take hold. Several scientists, including Lord Kelvin, hinted that life came to Earth on otherworldly “stones” that started life on Earth. In 1973, Leslie Orgel and Nobel Prize winner Francis Crick published the idea of “directed panspermia,” which means that an advanced life form sent life to Earth for a purpose. A theory that has support today.
Scientists supporting the theory
Stephen Hawking, among others, was one of the promoters of this theory. In fact, Panspermia is one of the reasons why Hawking believed that humanity should turn to more space exploration.
While it may be hard to imagine these “hitchhikers” of life speeding through space, it’s actually something that happens quite often. The high-speed meteorites that constantly hit the planet in its early days could have been the precursors of life, bringing building blocks for life to emerge: organic molecules that would form the first primitive cells. Certain types of carbohydrates and lipids would have been necessary to form life. Amino acids and parts of nucleic acids would also have been necessary for life to form.
Meteorites that fall to earth today are always scrutinized for these kinds of organic molecules as a clue to how the Panspermia hypothesis may have worked. Amino acids are common in these meteorites that pass through today’s atmosphere. Since amino acids are the building blocks of proteins, if they originally came to Earth in meteorites, they could congregate in the oceans to form proteins and simple enzymes that would be instrumental in bringing together the earliest, most primitive prokaryotic cells.
What was the first; the egg or the chicken?
Panspermia is an attractive theory because it does not explain the origin of life, simply the origin of life on Earth. The hypotheses do not necessarily contradict abiogenesis (an also ancient theory that exposes the spontaneous birth of living beings from inorganic matter); they simply change the origin elsewhere.
However, if life on Earth began elsewhere and traveled to our planet, the question remains: What is the origin of life?
