The Party Begins
(Published in The EarthSphere Blog; Cover Image: Building Blocks (by WM House & CF Lovelace; ArcheanArt)
I recently babbled on about the origins of Earth’s water in several articles. Since water is intimately tied to life on our planet, I wanted to pick up the story and put some context around life’s emergence.
The Seeds of Life
Water defines our planet, and it also defines the thin shell of life on our planet’s crust where the biosphere thrives. Exactly how life emerged is a mystery. We can only see backward in time 3.6 billion years to when life left some fingerprints in the geological record. Clearly, life started before then, but the specifics elude us. However, we understand the basic building blocks of our biosphere, and the appearance of the seeds of life marked the start of a long evolutionary journey.
The exact origin of the seeds of life has vanished in the primordial history of our planet. Perhaps inception was on a deep ocean floor in the extreme pressures and hellish temperatures around a hydrothermal vent. Or maybe it occurred in a warm puddle of mud as electric current pulsed through the water from lightning strikes. Some even argue it fell to Earth from outer space.
Regardless of its origins, we know deoxyribonucleic acid (DNA) provides the virile foundation of life shared by nearly all living organisms. Those few self-replicating organisms without DNA, like viruses and prions, use DNA’s close companion RNA (ribonucleic acid) to accomplish the task.
The genius of DNA is its embodiment of the nature of existence; the quality that life cannot do without. Its mantra could be characterized as, “if one of me is good, then two of me is even better.” Without the ability to self-replicate, life could not thrive and evolve.
Water and DNA
The structure and nature of DNA provide us with some hints about the conditions surrounding its formation. The molecular double helix never occurs in isolation. It is always coated with water molecules clinging to the DNA with the help of hydrogen bonds. Water is essential for the proper functioning of DNA and hence for the spread of life. As I have stated before, “without water, there is no life.”
DNA also has temperature requirements. Above its melting temperature, the two strands of a double helix will separate. DNA melting is also called DNA denaturation, and the melting point is dependent on numerous factors. But temperature is important, and at about 52 Degrees C the melting begins as the two helix strands start to separate.
The type of DNA also matters, and some DNA is more stable at higher temperatures. Various organisms live in temperature ranges outside of the norm. Psychrophiles thrive at temperatures around 0 °C, while thermophilic organisms survive at temperatures up to ∼100 °C.
A dizzying array of theories proposing mechanisms for DNA formation have been developed. A classic explanation has life, hence DNA, originating in a pool of water, rich with organic compounds. The sun provides heat energy to mix things up and get the ball rolling for life.
Others point out that in a pool with a limited volume of water, life would quickly go extinct as it uses the available chemical and nutrient base. What is needed, they insist, is a constant supply of the chemicals and compounds necessary to sustain continuous growth. The obvious sources for this stream of ‘food’ are subsea hydrothermal and volcanic vents. This thinking leads to theories about life developing around deep-sea vents where heat and chemicals are readily available.
The Problem of Entropy
But one of the problems facing all attempts at explaining the origins of life is the second law of thermodynamics: The total entropy of a system either increases or remains constant in any spontaneous process; it never decreases. Stated another way, it says all systems will tend towards increasing randomness and less order. Almost everyone putting serious thought into the origins of life agrees that its creation must be a spontaneous way to dissipate energy. This entropy constraint leads the theory of Thermodynamic Dissipation to explain DNA’s origin.
An interesting characteristic of DNA is its role as an organic pigment. Both RNA and DNA efficiently absorb and dissipate ultraviolet light in the 230–290 nanometer wavelength range (UV-C). This light spectrum range would have been part of the prebiotic, or pre-life, sunlight penetrating Earth’s early atmosphere.
Perhaps the miracle of life is a reflection of a metastable universe. The biosphere of Earth is a steady-state, open, thermodynamic system (a dissipative system in system control theory). Radiant energy, primarily from the sun, drives the biosphere. This energy provides the means to sustain life in a metastable system that will collapse when the sun’s energy disappears. Under this line of thinking, life then becomes the most efficient model for energy dissipation, given the particular temperature conditions of our planet.
Put more simply, DNA evolved as a means of increasing entropy. While this leads to locally decreasing entropy (increasing order) in the form of biological life, the net effect is an increase in the solar system’s entropy from the dissipation of the sun’s energy. The gist is, life spontaneously developed as part of a natural process. Given another water-rich solar system with a planet in the optimal temperature range for liquid water, we would expect it to happen again.
The EarthSphere Blog: Exploring life and the planet supporting it.
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Water molecules characterize the structure of DNA genetic material(Source: Science Daily)
Effect of Temperature on the Intrinsic Flexibility of DNA and Its Interaction with Architectural Proteins (by Rosalie P. C. Driessen, Gerrit Sitters, Niels Laurens, Geri F. Moolenaar, Gijs J. L. Wuite, Nora Goosen, and Remus Th. Dame; American Chemical Society)