What is a living thing?
This is not an easy question with an easy answer.
To put it bluntly, a living thing is either a bag of chemicals or a collection of many bags of chemicals.
The vast majority of life on Earth is comprised of single celled organisms (one bag of chemicals).
Multicellular organisms, like humans, are actually a collection of single-celled organisms that work in concert with one another.
Without the cells of the brain or the heart, the rest of the body would die.
In essence, we are a collection of many bags of chemicals that totally rely on one another.
The Building Blocks of Life
Life is basically comprised of highly organized, organic (carbon-based) molecules.
There are four main types of molecules found in all living things on Earth:
- Amino Acids: Amino acids are the building blocks of proteins. Proteins are what make up your muscles, but even more than that, proteins are basically the work horse of every cell in your body. Almost all cellular functions are carried out by proteins.
- Fatty Acids: Fatty acids are chains are hydrocarbons (hydrogen and carbon bonded together) that are used to make lipids. Lipids are integral to cell membranes because of their ability to create a barrier that separates the inside of the cell from the outside environment. Fatty Acids are also used as energy storage (fat), but you probably already knew that.
- Sugars: Sugars are the prime energy source used by living things. The most common forms of sugar are either 5 or 6-sided carbon molecules. Sugars can be strung together to make structures like the bark of a tree or the cell wall of a bacterium. More importantly, these molecules can also be broken down by proteins to create usable energy.
- Nucleotides: These molecules are actually an amalgamation of a 5-sided sugar, phosphates, and a ring comprised of nitrogen. Your DNA is actually made up of long chains of nucleotides that encode genetic data. Also, as mentioned previously, chemical energy in your cells are actually stored in the phosphate bonds of a nucleotide called ATP (Adenosine Tri-Phosphate).
The Earth before life began was a very inhospitable place. There was very little oxygen (O2) in the atmosphere.
According to Duke University, asteroid impacts released water (H2O) which rose into the atmosphere to combine with carbon dioxide (CO2) which formed very thick clouds over the Earth’s hot, molten surface.
Over time, the surface of the Earth began to cool, leading to rain.
The Rains cooled the Earth’s surface and formed solid rock, oceans, and rivers.
The Origin of Life
It is believed that the gases found in the atmosphere of early Earth was comprised of methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O).
They placed these molecules into a flask that was heated. This formed clouds that rose into a collection area of the apparatus.
Electrical currents then bombarded the molecules in the cloud which simulated early Earth lightning storms.
At the end of the one week, 10-15 percent of the molecules were now in organic forms.
Two percent of these organic molecules formed into amino acids.
Later in 1961, according to Duke University, a scientist named Juan Oro found that amino acids can be made from Hydrogen cyanide (HCN) and ammonia (NH3) in an aqueous solution (solution in which the solvent is water).
Hydrogen cyanide and ammonia were common in the early Earth.
Oro successfully was able to synthesize both amino acids and the base adenine, which is part of the nucleotide ATP mentioned earlier.
Other theories include the possibilities of these molecules coming from space through asteroid impact or from hot hydrothermal vents in the depths of the oceans.
Whatever the case may be, these building blocks would have to exist in order for life to develop.
Abiogensis: How does chemistry become life?
This is a very hard question to answer, but some interesting suggestions and hypotheses have been formulated.
Abiogenesis (pronounced "A-bio-genesis") is the study of how biological life could have arisen from inorganic matter through natural processes.
Abiogenesis encompasses where organic molecules come from, which we have covered, and how these molecules became ordered and able to be replicated (passed down from generation to generation).
- The Pre-biotic (before life) environment contained many simple forms of fatty acids. These fatty acids can spontaneously form vesicles, which are like microscopic soap bubbles. Not only has Dr. Jack Szostak proved this can occur, but researchers that I share my laboratory with at Saint Joseph’s University have actually performed this.
- These simple bubbles were not as good as the ones used by our cells today. This means that small organic molecules could diffuse, or pass through, the barrier.
- These bubbles (vesicles) can grow and divide just like current cells by purely mechanical means. They can grow by incorporating other fatty acids, and divide by coming in contact with waves, currents, or rocks in the oceans.
- When it comes to the genetic code, the pre-biotic environment was rich with many different types of nucleotides, not just DNA and RNA.
- Current research shows that chains of simple nucleotides can self-polymerize, meaning they can grow by connecting more nucleotides in a chain via simple chemistry, no proteins are needed. Our cells require complex proteins in order to perform polymerization mechanisms like replication and transcription.
- Essential self-polymerization is replication (making a new nucleotide chain for the next generation). In essence, this is reproduction at a very simple, chemical level. In order to become life, however, something interesting must happen. As our simple vesicles containing these nucleotide chains float around the ocean, they will encounter hydrothermal vents. The increased heat allows more nucleotides to diffuse through the vesicle. Acting as a template, our simple nucleotide chain will begin to self-polymerize itself, creating a new vesicle with exactly the same genetic information.
- This is where competition comes into play, the vesicles containing the best, most stable, or fastest replicating chains, are more likely to survive. If this sounds familiar to you, it’s because this is essentially how works: survival of the fittest.
- Most of the early beneficial mutations to these simple genetic codes, would involve a change to only the most common nucleotides and the ones that would replicate faster.
- Over time, these nucleotide chains would incorporate enzymatic activity (ability to do work in the cell) and even make fatty acids from the outside environment.
So, Where Does Life Begin?
I understand that this process may be hard to follow, but I have uploaded videos with images and clips to help you understand this process.
There is no finite point in this process where someone can clearly indentify life from purely chemical mechanisms.
Even your cells in your body are driven by pure chemistry.
All of our cellular machinery and their processes are driven by randomness and the laws of physics and chemistry.
I argue that the collective "consciousness" of these mechanisms is what gives life purpose and meaning.
Looking at this simple form of “life”, I realize that it is very hard to see how complex creatures like us could evolve.
Just remember, life had over 3.5 billion years to get increasingly more complex.
I find it amazing that our origins lie in simple organic chemistry. It is kind of amazing when you look at how many different and wonderful forms of life are on this planet.
Think about it!