Seeds of Life
Biosphere Earth Science Feature 2

The Seeds of Life

The when, the how, and the why regarding the origins of life’s fundamental building blocks remain unknown. The origin of the seeds of life disappeared 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. But, perhaps it occurred in a warm puddle of slime 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 cannot deny that deoxyribonucleic acid (DNA) provides the virile seeds 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 that it embodies the “sine qua non” 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. There would be no biosphere on our planet. I would not be writing this article.

The beginning

The question of when life began on earth is a developing story. But the most common answer is that the earth is about 4.5 billion years old and the oldest uncontroversial evidence of life flourished some 3.4 billion years ago. These ancient forms of early life were bacteria – specifically, cyanobacteria. The evidence in question for establishing earliest life at 3.4 billion years comes from fossil stromatolites in Western Australia. 

If you aren’t a stromatolite enthusiast, then picture something like a big head of cabbage buried in sediments and turned into rock. When you break open the rock and see it 3.4 billion years later, you can recognize it from the rounded shape of a bioherm composed of thin layers that stack up one-on-another. 

The original bioherm was composed of cyanobacteria (blue-green algae) that trapped sediment on the outer layers of the mound to give it the layered, cabbage-like look. Stromatolites are one of the world’s oldest life forms, but they still exist today. Shark Bay, Australia is famous for its present-day stromatolites.

Water

These observations on stromatolites are impressive, but they don’t answer the question about when DNA, the seed of life, appeared. Cyanobacteria represent a leap up the evolutionary chain from a mere DNA molecule. So DNA must predate the oldest known stromatolites.  We don’t know exactly how the first DNA molecules came into being. But most researchers have focused on the need for a liquid solvent to help develop a molecular soup where individual molecules can mix and mingle. The most likely liquid solvent to meet these needs would be water. 

A study of zircons from some of the oldest rocks on the planet provides evidence of water on earth as early as 4.4 billion years ago, not long after the formation of the planet. Therefore there is a one billion year period (3.4 billion years to 4.4 billion years) in which DNA formed. Then its formation kick-started the evolution of life as we know it. Various recent studies have pushed the possible envelope for life, stretching it back to 4.2 billion years ago. So indirect evidence from these studies raises the possibility that DNA formed sometime within the first 300 million years after the formation of the planet. 

Origins

It seems legitimate asking if DNA evolved, or was it just placed here on earth from the beginning of the planet’s history? Some researchers have speculated that the seeds of life were introduced to earth via bombardment with meteorites and space dust. Meteorites as old as the earth have been analyzed and found to have traces of water and organic molecules. Interplanetary and interstellar space dust continually bombard the planet, and organic molecules have been found in this dust. So, is there validity in recent investigations supporting a model that DNA traveled with the space dust. Did life start on Mars and travel to earth?

If DNA development is purely in-situ to earth, then addressing how the first DNA formed is more difficult than pinning down approximately when it happened. The famous Miller experiment of 1952 demonstrated the creation of amino acids (organic compounds critical to life) in the laboratory. A mixture of water, methane, ammonia, and hydrogen exposed to heat and electric current produces these amino acids.

Similar experiments using the basic Miller chemical mix with some additional inorganic sediment added were run. They used high temperature and high-pressure conditions when creating new amino acids. Likewise, zapping a clay and chemical soup with a high powered laser produces amino acids from where none existed before. The laser in that experiment simulated large-scale impact events on the earth’s surface.

Key components

The production of these amino acids by various means is impressive, but while amino acids are essential organic components of proteins, and proteins are critical to the proper functioning of cells, what we really want to understand is DNA, not just its components. DNA is the “master builder” that determines what proteins are produced and when they are produced. Instructions in the DNA control the biological functioning of a bacterium, and they also control the biological functioning of a human. 

The DNA of all organisms from bacterium to human uses the same chemical and physical components. The same six molecules control whether you are a jellyfish or a human. The magic six includes a five-carbon sugar molecule called deoxyribose, a phosphate molecule, and four different nitrogenous based molecules (adenine, thymine, cytosine, and guanine).

These six molecules are used in building nucleotides. Each nucleotide has one sugar molecule, one phosphate molecule, and then one of the four possible nitrogenous base molecules. At a basic level, the sequence these nucleotides use to pair up and form long spiraling chains determines whether I am floating brainlessly on the ocean currents or writing a blog.

These facts in and of themselves do not provide a strong boost to self-image. I prefer thinking I am a more chemically advanced lifeform, but sadly my jellyfish friend and I originated from the same 6 molecules.

How and why

We have narrowed down “the when” to probably being in the first 300-900 million years after the earth formed, but we really don’t know “the how.” We can envision several ways to provide the requisite amino acids, but what would cause them to organize into the first DNA. Was it merely a coincidence, a stroke of luck in a world of random chance? In a universe controlled by entropy and a progression towards randomness, why should complexity and increasing organization dominate the surface of our planet?

These types of questions don’t go away even if DNA arrived on the earth by meteorites or cosmic space dust. If life is more than a one-off, random event, then there needs to be an energy-based answer to the question of “why?” Does DNA represent an end state of quantum stability or is it a reflection of a metastable state. (Electrons are in end-state stability when they are at their lowest energy level. If excited, the same electron can be in a higher energy state making it metastable.)  

A metastable solution

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. The seeds of life developed because it is the optimal chemical system to propagate a biosphere that covers the entire planet.

 While this particular idea supplies speculation on “the why” of DNA, it falls far short of providing any real answer. The origin of DNA remains an unknown. Future scientific research may eventually provide us with answers to “the how” and “the why,” but for now we must simply embrace the mystery.


Sources

Earliest evidence of life on Earth ‘found’ – https://www.bbc.com/news/science-environment-39117523 Also:

Is the universe a stable quantum system?  – https://phys.org/news/2014-09-universe-stable-quantum.html Also:

Cyanobacteria bloom Baltic Sea (Source: NASA) (Modified) – https://commons.wikimedia.org/wiki/File:Nodularia_bloom.jpg – This file is in the public domain in the United States because it was solely created by NASA. NASA copyright policy states that “NASA material is not protected by copyright unless noted

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.