Life may not have started in a primordial soup but a hive
Creation stories are common in mythology. African Bushmen believed that people and animals started out living underground in an Eden-like state of peace and harmony. God led them up to the surface and told humans not to build any fires. When the sun went down, the people became cold and couldn’t see and so disobeyed God by building a fire. Stories like this don’t get into how people and animals came about in the first place. They were just kind of always there. Other stories such as that of the Bible have God creating life.
These stories were not intended to be scientific theories but rather established the relationship between people and creation and explained the human condition. Yet, for billions of years, the fossil record and geologic record demonstrate, there was no human condition because there were no humans.
The publication of Charles Darwin’s Origin of Species revolutionized our understanding of life and how complexity could arise without mysterious divine intervention. Although the original theory had many flaws, it was refined and assumed that there was a connection to the chemistry that made up life now.
Darwin proposed in the 1859 landmark book that all species derived from common ancestors and, working backward, he conjectured that “all the organic beings which have ever lived on this earth have descended from some one primordial form.”
Yet, the conditions for this origin of life were not well understood. After all, why isn’t life originating all the time? Why did it only happen billions of years ago? There must be something about the conditions of the early Earth, the lack of oxygen producers, for example.
In 1924, a 30 year old Russian biochemist Alexander Oparin proposed that life began in a thick, hot soup full of organic molecules in a bestselling book called The Origin of Life. This soup would have been literally edible (for primitive life) when heated. Organic molecules created in the atmosphere from lightning, interactions with the solar wind, UV light, and meteorites would have rained down on the early oceans. Deep sea hydrothermal vents, hot springs, and volcanoes would have provided the heat to jump start life.
Oparin speculated that life formed spontaneously out of this primordial soup.
Since his book was published, luminaries such as biologist J. B. S. Haldane, physicist J. D. Bernal, biochemist Melvin Calvin, and chemist Harold Urey all worked to flesh out the details.
In 1953 Stanley Miller, along with his advisor Urey, conducted an experiment they combined water, hydrogen, methane, and ammonia gases in a sealed aparatus. They then supplied steam to mimic water vapor in the early atmosphere. Sparks from electrodes simulated lightning while a condenser below turned the vapor into liquid which was then sampled.
This groundbreaking experiment demonstrated how the early Earth’s atmosphere could produce amino acids from simple chemistry and created the field of experimental prebiotic chemistry, the study of how life could arise from inanimate molecules.
Not long after, in 1962, Alexander Rich proposed a theory for how evolution got jumpstarted called the RNA world. This theory proposes that the original replicator that allowed natural selection to take over were strands of RNA.
RNA is DNA’s cousin. Able to store genetic information as well, it is simpler because of its single strand structure. In the RNA world theory, these strands stored genetic information and catalyzed chemical reactions in early cells. Sometime later RNA transitioned to the more stable DNA.
While the RNA world hypothesis has plenty of evidence in its support, it really doesn’t tell us how life got started. The strong version of the theory says that RNA formed spontaneously and became the only replicator on the early Earth. That, however, is highly unlikely both because of its improbability and also because we can see in modern living cells structures that are likely more ancient. For example, enzymes such as metalloproteins contain iron-sulphur clusters in their center. These clusters may come from structures more ancient than RNA.
Minerals, although inorganic, like greigite enabled the beginnings of photosynthesis, likely long before RNA appeared. At best, there is a missing link between the production of amino acids and the appearance of RNA that we cannot explain.
Then there is the soup itself. How could a primordial soup even form given that it is dissolved in a literal ocean of water?
A competing theory is that life formed from carbon dioxide on mineral pyrite on the surface. As the pyrite oxidized into iron monosulphide and hydrogen sulphide, metabolism could begin.
This has the same problem as the soup. How can replication get started unless it is contained within a small area for a long, long time?
Another problem of the origin of life is analogous to the chicken-and-egg problem but it is a chicken-feed-and-egg problem. Which came first? Eating or reproducing? Or did they happen at the same time?
In order to use the energy in nutrients, you have to metabolise them. They don’t just magically become part of your structure and allow you to live. They also have to drive your body at the cellular level.
To metabolise nutrients, you have to have a chemical reaction going on in each of your cells that extracts energy. In our case, our mitochondria generate ATP as an energy source.
Mitocondria are believed to descend from a free living organism called a prokaryote which developed a symbiotic relationship with our cells. There are still prokaryotes around and they have a lot in common with mitochondria.
Some time billions of years ago, our mitochondria found protection by living within cell walls or membranes while our cells found the power production of the mitochondria useful. This may explain why mitochondria have their own vestigal genomes, separate from ours.
Besides the metabolism problem, we also have a problem of how we went from soupy organics to cell membranes. Membranes are sophisticated protection mechanisms but they also keep all the metabolic and replication components of the cells together and they also are critical to how cells produce energy in order to grow and divide. All of these properties had to have predated the membrane’s evolution for it to have even been selected as an advantageous trait.
The solution to all these problems is that life emerged about 3.8 billion years ago in small compartments at the bottom of the ocean.
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