Scientists have reason to think that the first living cells on Earth came about through a natural process called Chemical Evolution. What is Chemical Evolution, how does it work, and how is it different from Biological Evolution?
To answer these questions, we’ll first dissect the terms and then look at an example of how Chemical Evolution can take simple molecules and organize them into complex structured systems, similar to those found in living cells.
What is chemical evolution?
The word “Evolution” means change over time. Biological Evolution deals with changes in things that can reproduce: living creatures make copies of themselves. The change over time that we see in Geological Evolution is not just random chance. Often it is adaptive change.
Populations become better able to survive and reproduce within their environments. When conditions are right, biological evolution can even drive a species to develop brand new characteristics and abilities. For this to happen, biological evolution typically requires three conditions:
Many species have smooth-edged leaves. English Holly, however, is covered in spikes that protect the plant from deadly predators. How did these weapons first evolve? When a holly plant reproduces, its offspring often show a random variation. They are slightly different from their parents and slightly different from each other.
In a forest filled with grazing animals, individual plants which happened to be harder to eat than their siblings are more likely to grow up and have children of their own. By being difficult to survive in, nature selects who gets to reproduce and pass on their new traits and who does not. In this case, mutations that caused these leaves’ vanes to extend past their edges gave a brand new weapon!
The discovery of biological evolution was an incredible breakthrough in science. It explained how new complex traits and abilities develop naturally in living things. The problem is Biological Evolution depends on reproduction to work. Reproduction, however, is a highly complex process in itself. This begs the question: How did reproduction first evolve?
To try and solve this mystery, many scientists are looking into Chemical Evolution. Chemical evolution refers to changes in things that need not be reproduced. Examples could be individual molecules or entire chemical systems. A chemical system is a group of molecules that interact with each other. Molecules, structures, and chemical systems almost always evolve, but they often evolve towards simplicity.
Solid iron corrodes into rust when it comes in contact with the water. Proteins break down when exposed to too much heat. Suppose simple chemistry is to give rise to something advanced enough to reproduce. In that case, there must be situations in which chemical systems can grow in complexity, form new structures, and gain new functions. For this to happen, reproduction, which is needed in biological evolution, can be replaced with a much simpler process: repetitive production.
On planet Earth and throughout the universe, powerful natural events occur in regular cycles: The heating and cooling off day and night. The repetitive eruptions, volcanic geysers, the rise and fall of ocean tides. These events repetitively produce or give birth to new molecules and chemical systems. These products increase over time and often develop new abilities as they interact with their environment.
How chemical evolution work?
The instructions are necessary to build every protein in an organism. In a process known as transcription, a molecular machine first unwinds a section of the DNA helix to expose the genetic instructions needed to assemble a specific protein molecule.
Another machine then copies these instructions to form a molecule known as messenger RNA. The slender RNA strand carries the genetic information through the nuclear pore complex when transcription is complete. The gatekeeper is for traffic in and out of the cell nucleus.
The messenger RNA strand is directed to a two-part molecular factory called a ribosome. After attaching itself securely, the process of translation begins. A molecular assembly line builds a specifically sequenced chain of amino acids inside the ribosome. These amino acids are transported from other parts of the cell.
Then they linked into chains, often hundreds of units long. Their sequential arrangement determines the type of protein manufacturer. It moves from the ribosome to a barrel-shaped machine when the chain is finished. It helps fold it into the precise shape critical to its function. After the train is folded into a protein, it is then released and shepherded by another molecular machine to the exact location needed.
Process of chemical evolution
Let’s observe the fatty acid. It’s a collection of carbon, hydrogen, and oxygen atoms stuck together in a specific pattern. Fatty acids are many complex molecules that living cells use inside their bodies. They build fatty acids with atoms they get from their environment.
Scientists used to think that living cells were the only things that consistently built fatty acids. Lab experiments have shown that when simple common gases: carbon monoxide and hydrogen. They are heated up with minerals like those found in the Earth’s crust, a variety of complex carbon molecules, including fatty acids, begin to grow!
Living cells are not needed! It can happen naturally in underground chambers heated by the Earth’s Magma. As pressure builds, these molecules can belch up into pools of water, where a simplified version of Natural Selection then takes over. Most particles blasted into water will either float, or they will sink. Nature selects against them staying in the watery environment.
Fatty Acids, however, remain suspended in warm water, growing in number as the cycle repeats. When fatty acid concentrations are high enough, they bunched together, automatically self-assembling into a stable ball! It happens because water molecules are attracted to the oxygen heads of the fatty acids, sort of like a magnet. But water repels their oily carbon tails.
When fatty acids pass near each other, their tails are pushed together by water, forming a ball. As fatty acid collections continue to increase, they join together to make large skins! If fluctuations in the skins make the edges touch, water forces those fused. The result is a stable hollow container similar to a living cell’s membrane or skin!
These containers have a brand new ability. They can trap other molecules inside, acting as an entirely new environment for chemical evolution to continue working within! It’s important to note that these membranes are not considered living creatures. They can’t reproduce on their own the same way living cells do.
The development of these membranes and many other molecules and chemical systems that scientists have observed demonstrate a fundamental principle: Chemical Evolution can give new characteristics and abilities. Because of this, scientists hypothesize that chemical evolution could give rise to systems that are fully capable of reproduction under the right circumstances!
If they are correct, this will bridge the gap between Chemical Evolution and Biological Evolution, demonstrating that chemistry can indeed give rise to life! Scientists at the Center for Chemical Evolution and other research groups worldwide are working hard to test this hypothesis.
So to sum things up, the main difference between Chemical Evolution and Biological Evolution is that Chemical Evolution can produce new characteristics and abilities without depending on reproduction. Because of this, Chemical Evolution is being investigated as a possible cause for the origin of life.
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Lineweaver, Charles H. “The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way.” Science. 303 (2004): 59-62.
Perry, Randall S., and Vera M. Kolb. “On the Applicability of Darwinian Principles to Chemical Evolution that Led to Life.” International Journal of Astrobiology.
Rasmussen, Steen, et al. “Transitions from Nonliving to Living Matter.”
Knoll, Andrew H. Life on a Young Planet: The First Three Billion Years of Evolution on Earth.