The origin of life is still a mystery to science, even though evolution is now a proven fact. Learn about four theories hoping to shed light on this enigma.
One of the most annoying things that children do is ask a long series of “why” questions. “Why are you getting your keys?” “Because we’re going for a ride in the car.”
“Why?” Because we need to go shopping.” “Why?” “Because we’re running out of food.” “Why?” “Because we keep eating it.” Why?” “Just get in the car.”
As we get older, we learn to contain this impulse (out loud, at least) but our minds still do it. We’re inquisitive creatures by nature. We like to work our way back to the root cause of everything.
DARWIN WANTED TO UNDERSTAND THE DIVERSITY OF LIFE
Charles Darwin wanted to understand the diversity of life. Why were there so many different forms of life, and where did they all come from?
His answer was evolution, which is all well and good, but it only leads us to another question. There must have been one tiny living creature at the very beginning of the natural selection process. Where did it come from and how did it form?
Darwin definitively explained the origin of species in his book of the same name. Even so, he never really answered the deeper question of the origin of life itself.
ORIGIN OF LIFE WAS BEYOND SCIENCE AND BESIDE THE POINT
Biographers think that he deliberately avoided that question in his books. He felt that, in his day, how life began was beyond science and also beside the point.
In the third edition of the Origin of Species, he wrote, “It is no valid objection that science as yet throws no light on the far higher problem of the essence or origin of life.”
Biologists call this topic abiogenesis, and it wasn’t Darwin’s goal. Even so, that doesn’t mean it’s not a question we’d all love to see answered.
HOW LIFE AROSE 3.5 BILLION YEARS AGO IS STILL A MYSTERY
It’s been over 160 years since Darwin wrote the Origin of Species and we still don’t have a clear answer to the question of how life began. Scientists distinguish between evolution (descent with modification by means of natural selection), which is a proven scientific fact, and abiogenesis (how life arose 3.5 billion years ago from inorganic matter), which is still a mystery.
There are theories, of course. We’ll take a look at four of the most influential ones here.
FIRST THEORY: LIGHTNING
The best-known theory on the origins of life on earth looks at lightning. Darwin famously suggested that life may have formed in a “warm little pond” with the right combination of “ammonia and phosphoric salts, light, heat, electricity etcetera present.”
The classic experiment on abiogenesis put Darwin’s hypothesis to the test. In 1952, Stanley Miller and Harold Urey wanted to simulate the effects of lightning on a habitat like the primordial soup of Darwin’s pond.
They put water, methane, ammonia and hydrogen into a sterile container. heated it up and let some steam drift into it. Then they used electrodes to send sparks of electricity through the solution and the vapour to simulate lightning.
ELECTRICITY PRODUCED FIVE AMINO ACIDS IN THE LAB
They let the flask and its contents cool down and settle. After a week, they identified five amino acids, the molecules of life, in the liquid that weren’t there before.
The University archived the samples and later researchers found that chemical reactions in them had actually produced at least 20 amino acids from inorganic chemicals.
Critics disagree over whether Miller and Urey were right about the chemistry of the early earth. Besides, cooking up some amino acids in the lab isn’t the same thing as mixing up a living cell. Still, the Miller-Urey experiment is a landmark in biology.
SECOND THEORY: MOLECULES
The second way we can look at the origin of life is to dig deeper into the chemical building blocks of life. One challenge here is a kind of chicken-and-egg conundrum. Proteins come from DNA and DNA comes from proteins.
So, how did this relationship start? The answer might come from what biologists call the RNA World hypothesis. If you remember your high school biology, you’ll recall that RNA is a simpler molecule than DNA that can also carry genetic codes.
Today, RNA turns certain genes on and off in living things. Back then, it could have worked like an enzyme to help DNA form along with other proteins.
RNA COULD HAVE WORKED LIKE AN ENZYME TO HELP DNA FORM
Again, that doesn’t really answer the question. If we accept this theory, we have to explain how RNA got here because it’s a fairly complex molecule itself and so are the other nucleic acids that scientists know were around at the time.
Other theorists working from the chemistry perspective think we have to start more simply. Smaller chemicals could have reacted with each other in shorter cycles.
Researchers have proposed that the more basic molecules might have had tiny capsules. These might have worked like cell membranes and gradually collected into larger molecules.
The idea here is to start with the chemical reactions, i.e. the metabolism, first. The genetic information processing would have evolved later on.
THEORY 3: DEEP-SEA VENTS
This isn’t really a complete answer as to how cells formed from molecules, though. More recently, some scientists have come up with a third idea based on life starting in deep-sea vents.
These hydrothermal vents form in the seabed rock. They churn out warm, alkaline water into the seawater, which is cooler and a bit more acidic.
Sea creatures gravitate to the warm, pleasant habitat around deep-sea vents. There’s a lot of biodiversity near the ocean floor around them.
CREATURES GRAVITATE TO HABITAT AROUND DEEP-SEA VENTS
The vents form chimneys and the chimneys have tiny pores in their walls. These pores could have worked like tiny forms where organic molecules, then self-replicating molecules and finally living organisms could have developed over a few million years.
Critics of this theory point out that complex molecules like RNA and DNA form in places with alternating wet and dry cycles. Since the ocean floor is always wet, this couldn’t have been the case there. The debate rages on.
THEORY 4: METEORITES
Our fourth and final theory says that life originated in outer space. Modern cells could have made it to Earth on meteorites blown off into space by asteroids crashing into other planets, like Mars. Comets could even have carried living cells here from outside the solar system.
This idea is called panspermia, and recent discoveries show that it’s possible. We know that meteorites have travelled from Mars to Earth, for example.
Experiments on the International Space Station have shown that, with light radiation shielding, living cells can survive in outer space for years. It only takes seven months for a meteorite to travel from Mars to Earth.
living cells can survive in outer space for years
Scientists don’t know at this point whether life ever existed on Mars. Keep in mind, though, that Mars was very different in the past, with a thicker atmosphere and liquid water.
If we go back to our childhood habit of asking why, we realize that this explanation still doesn’t answer the question. If meteors or comets brought life here from somewhere else, how did life form in that other place? It’s still a mystery.
Once we have mature cells in place, scientists have a much better handle on what happened from there. Darwin didn’t know about DNA, so he didn’t talk much about molecules, but tiny variations in our genetic code cause what he called “descent with modification.”
CHANGES IN GENETIC CODE CAUSE “DESCENT WITH MODIFICATION”
Most of those modifications make things worse, and many more don’t make much difference. Despite this, once in a while, a modification will give an individual a slight advantage that lets it live longer and gives it a better chance to reproduce.
The natural environment imposes the discipline that Darwin called natural selection. It’s not the strongest or the smartest that survive and evolve. It’s those who are best suited to their environments.
Abiogenesis is still one of the great mysteries of science. Whenever we see such diverse, competing theories we know that we need a lot more facts and evidence before we can answer the question at hand.
WE NEED A FACT-BASED STORY THAT EXPLAIN’S NATURE’S ORIGINS
Even so, it’s important that we do find the answer eventually. To restore meaning to our lives, we need a fact-based story that explains nature’s origins and our place in it. The origin of life is a big gap in the plot-line of our story.
We always have more to learn if we dare to know.
A Production of Amino Acids Under Possible Primitive Earth Conditions
The RNA World and the Origins of Life
The Physiology and Habitat of the Last Universal Common Ancestor
Panspermia: A Promising Field of Research
Life Began Earlier Than Thought
Did Life Begin in Soda Lakes?
Is it a Bird? Is it a Bee? No, it’s a Hummingbird Moth