- Part two: A split in the ranks of scientists -
- Part three: in search of the first replicator -
- Part four: the energy of protons -
- Part five: so how do you create a cell? -
- Part Six: The Great Unification -
Today, life has conquered every square centimeter of the Earth, but when the planet first formed, it was a dead stone. How and when did the landmark transition take place? How did life begin? One can hardly think of a more serious, big and complex question. Throughout most of human history, no one doubted that this was the business of the gods. Any other explanation was unthinkable.
No more. Over the past century, many scientists have tried to figure out where the first life could begin. They even tried to recreate the moment of Creation in their laboratories: create a completely new life from scratch. So far, no one has succeeded, but we have come a long way. Today, many scientists studying the origin of life are confident that they are on the right track - and they have experiments that underpin their confidence in this.
This is the story of our efforts to figure out our true origins. It is a story of obsession, struggle, and brilliant creativity that led to some of the greatest discoveries in modern science. The desire to understand the origins of life sent men and women to the most remote corners of our planet. Some scholars were considered devils in the flesh, while others continued to work under the thumb of brutal totalitarian governments.
This is the story of the birth of life on Earth.
In fact, dinosaurs lived not so long ago.
Life is old. Dinosaurs - the most famous extinct creatures - appeared 250 million years ago. But life began much, much earlier.
The oldest known fossil record is about 3.5 billion years old, 14 times as long as the oldest dinosaurs. But the fossil record can take us even further. For example, in August 2016 alone, scientists discovered fossilized microbes that are 3.7 billion years old.
Promotional video:
These wavy patterns may be 3.7 billion years old
The Earth itself is not much older, it is 4.5 billion years old.
Assuming that life originated on Earth - which seems reasonable, given that we still haven't found it elsewhere - then this must have happened in the billion years that elapsed between the formation of the Earth and the appearance of the oldest known fossils.
By narrowing down the range of times life may have appeared, we can make educated guesses about how it happened.
The tree of life: most bacteria and archaea
Since the 19th century, biologists have known that all living things are made up of "cells": tiny sacs of living matter that come in all shapes and sizes. Cells were first discovered in the 17th century, thanks to the invention of the first microscopes, but it took over a hundred years to realize that they were the basis of all life.
You certainly do not look like a catfish or a tyrannosaurus, but a microscope will show that you are made of almost the same cells. Like plants and mushrooms. But so far, the most numerous form of life is microorganisms, consisting of one cell. Bacteria are the most famous group and can be found everywhere on Earth.
In April 2016, scientists presented an updated version of the "tree of life": in a sense, the family tree of every living species. Almost all branches are bacteria. Moreover, the shape of these branches suggests that bacteria were the common ancestor of all life. In other words, every living thing - including you - came from bacteria.
It turns out that we can more accurately define the problem of the origin of life. Using only materials and conditions that were on Earth 3.5 billion years ago, we must make a cell.
How difficult will it be?
Whole living cell
First experiments
Throughout most of history, no one considered it necessary to ask how life came about, since the answer seemed obvious. Until the 1800s, most people believed in "vitalism." This is an intuitive idea that living things are endowed with a special, magical property that distinguishes them from inanimate objects.
Vitalism has often been associated with religious beliefs. The Bible says that God used the "breath of life" to revive the first people, and the immortal soul is a form of vitalism.
There is only one problem. Vitalism is complete nonsense.
By the early 1800s, scientists had discovered several substances that seemed unique to life. One such compound was urea, which was found in urine and excreted in 1799. Only this still fit into the concept of vitalism. Only living things were able to produce these chemicals, so they apparently were charged with life energy and this made them special.
But in 1828, German chemist Friedrich Wöhler found a way to make urea from a common chemical, ammonium cyanate, which had no obvious connection with living things. Others followed suit, and it soon became clear that the chemicals of life could be made from simpler chemicals that had nothing to do with life.
Friedrich Wöhler, German chemist
This was the end of vitalism as a scientific concept. But people found it difficult to part with this idea. To many people it seemed that to say that there was nothing "special" about the chemicals of life was like taking away its magic from life, making it mechanical or soulless. And, of course, it was contrary to the Bible.
Even scholars have tried to save vitalism. As early as 1913, the English biochemist Benjamin Moore fervently promoted the theory of "biotic energy", which was the same vitalism, but with a different name. This idea had a strong emotional overtones.
Even today, however, this idea sometimes pops up here and there. For example, there are many science fiction stories in which the "energy of life" can be increased or sucked out. Think of the "regeneration energy" used by the Time Lords in Doctor Who. It seems unusual, but this is a very, very old idea.
After 1828, however, scientists had good reason to seek a "godless" explanation for the first appearance of life. But they didn't. It would seem that this topic needs to be investigated, but in fact the mystery of the origin of life has been ignored for decades. Perhaps they were still too attached to vitalism to take the next step.
Charles Darwin showed that all life descended from one common ancestor
Instead, the giant leap forward in biology in the 19th century was the theory of evolution developed by Charles Darwin and others.
Darwin's theory, set forth in The Origin of Species in 1859, explained how all this diversity of life could have emerged from a single common ancestor. Each individual species was no longer created by God, but descended from an ancient organism that lived millions of years ago: the last universal common ancestor.
This idea turned out to be extremely controversial, again because it did not fit the Bible. Darwin and his ideas came under attack from partly outraged Christians.
The theory of evolution did not say anything about how the very first organism appeared.
Darwin believed that life appeared in a "warm little pond"
Darwin knew that this was a profound question, but - perhaps fearing new attacks from the church - he dared to discuss it only in 1871. The upbeat tone of the letter shows that he knew the deep meaning of this question:
“But if (and oh, what a big“if”) we could imagine a small warm pond with all kinds of ammonia and phosphorus salt - with light, heat, electricity - in which a protein compound would be chemically formed, ready to go through even more complex changes …"
In other words, what if there was once a small body of water filled with simple organic compounds and bathed in sunlight? Some of these compounds might combine to form a semi-living substance like a protein that could begin to develop and become more complex.
This idea was superficial. But she formed the basis for the first hypothesis of the emergence of life.
Curiously, this hypothesis appeared in the USSR.
Alexander Oparin lived and worked in the USSR
During Stalin's time, everything was under the control of the state. Even the ideas of people, biologists, not related to communist politics. Remarkably, Stalin actually prohibited scientists from studying conventional genetics. Instead, he promoted the ideas of the farmer Trofim Lysenko, which, in his opinion, were more in line with communist ideology. Scientists working in the field of genetics were forced to publicly support Lysenko's ideas in order not to end up in the camps.
It was in such a repressive environment that Alexander Oparin conducted his research in the field of biochemistry. He could work because he was a devoted communist: he supported Lysenko's ideas and even received the Order of Lenin, the highest award of the Soviet era.
In 1924 Oparin published his work The Origin of Life. In it, he outlined his vision of the origin of life, which was strikingly similar to Darwin's small warm pond.
The oceans formed after the Earth cooled down
Oparin tried to imagine what the Earth was like after formation. The surface was scorching hot as rocks fell from space. A hodgepodge of semi-expanded rocks containing a huge range of chemicals, including those based on carbon.
Eventually the Earth cooled down enough for the water vapor to condense into liquid water and the first rain began to fall. It filled Earth's oceans, which were hot and rich in carbonaceous chemicals. What you need for life.
At first, various chemicals interacted with each other to form many new compounds, some of which were complex. Oparin suggested that the molecules essential to life, sugars and amino acids, could have formed in the waters of the Earth.
Then some of the chemicals began to form microscopic structures. Many organic substances do not dissolve in water: for example, oils form a layer on top of water. But when some of these substances come into contact with water, they form spherical "coacervate" balls, which can be up to 0.01 centimeters across.
If you look at coacervates through a microscope, they behave very mobile, like living cells. They grow and change shape, sometimes divided into two parts. They can also pick up chemicals from the surrounding water, so they can end up with life-like chemicals. Oparin suggested that coacervates were the ancestors of modern cells.
Five years later, in 1929, English biologist John Burdon Sanderson Haldane independently proposed very similar ideas in a short article published in the Rationalist Annual.
By that time Haldane had already contributed a lot to the theory of evolution, helping to integrate Darwin's ideas into the developing science of genetics.
English geneticist J. Haldane
Like Oparin, Haldane described how organic matter could accumulate in the water "until the primordial oceans reached the consistency of hot, diluted soup." This would set the stage for the "first living or semi-living things" that formed and ended up in a thin film of oil.
It is significant that among all the biologists in the world, only Oparin and Haldane came to this. The idea that living organisms can be formed through simple chemical reactions, without God or even "life force", was radical. Like Darwin's theory of evolution before it, it too was a slap in the face of Christianity.
But it fit perfectly into the framework of the USSR. The Soviet regime was officially atheistic, and its leaders happily supported any materialistic explanation for profound phenomena like life. Haldane was also an atheist and a communist to boot.
“At that time, acceptance or rejection of an idea depended mainly on the individual: whether he was religious, whether he supported left-wing or communist ideas,” says origin-of-life expert Armen Mulkidzhanian of the University of Osnabruck in Germany. “In the Soviet Union, they were received with joy, because they did not need God. In the Western world, if you look at the people who thought in this direction, they were all leftists, communists and so on."
The idea that life was formed in a primordial broth of organic matter became the Oparin-Haldane hypothesis. She was neat and convincing, but there was one problem. She was not supported by any experimental evidence. And so it went on for almost a quarter of a century.
Harold Urey
By the time Harold Urey became interested in the origins of life, he had already won the 1934 Nobel Prize in Chemistry and helped build the atomic bomb. During World War II, Yuri worked on the Manhattan Project, collecting the unstable uranium-235 needed for the bomb's core. After the war, he fought to keep nuclear technology under civilian control.
He also became interested in the chemistry of space, in particular, what happened during the formation of the solar system. He gave a lecture one day and noted that there was probably no oxygen in the Earth's atmosphere when it first formed. This was the perfect complement to Oparin and Haldane's primary broth: fragile chemicals could be destroyed by contact with oxygen.
A doctoral student named Stanley Miller was in the audience and then approached Yuuri with a question: can this idea be tested? Yuuri was skeptical, but Miller insisted on his own. So in 1952 Miller began the most famous experiment on the origin of life.
Miller-Urey experiment
The settings were simple. Miller connected a series of glass flasks and fired four chemicals that might have been present on the early Earth: boiling water, hydrogen gas, ammonia, and methane. He then subjected the gases to repeated electric shocks to simulate the lightning strikes that were common on Earth in those days.
Miller found that "the water in the vials became significantly pinker after the first day, and by the end of the week the solution was red and cloudy." Apparently a mixture of chemicals has formed.
After analyzing the mixture, Miller discovered that it contains two amino acids: glycine and alanine. Amino acids are often referred to as the building blocks of life. They are used to form proteins that control most of the biochemical processes in our bodies. Miller built two essential components of life from the ground up.
The results were published in the prestigious journal Science in 1953. Yuri did something very unusual for senior scientists, taking his name off his job and giving all the credit to Miller. Despite this, the study is often referred to as the Miller-Urey experiment.
Stanley Miller in the laboratory
“The strength of Miller-Urey is that you can produce many biological molecules just from the atmosphere,” says John Sutherland of the Molecular Biology Laboratory in Cambridge, UK.
The details turned out to be incorrect, as later studies showed that the atmosphere of the early Earth was a different mixture of gases. But that doesn't change the fact. The experiment was a success, stimulated the public's imagination and exploded into quotes.
After Miller's experiment, other scientists began looking for ways to create simple biological molecules from scratch. The solution to the mystery of the origin of life seemed about to appear.
But then it turned out that life was more difficult than anyone thought. Living cells weren't just bags of chemicals: they were tiny tiny machines. Suddenly, building a cell from scratch proved to be much more difficult than scientists thought.
ILYA KHEL
- Part two: A split in the ranks of scientists -
- Part three: in search of the first replicator -
- Part four: the energy of protons -
- Part five: so how do you create a cell? -
- Part Six: The Great Unification -