“Life is really simple, but we insist on making it complicated.”
Confucius (551–479 BCE)
“Life does not merely reside on the planet; it is an extension of the planet. . .Earth is a stone that eats starlight and radiates song, whirling through the inscrutable emptiness of space—pulsing, breathing, evolving—and just as vulnerable to death as we are.”
Ferris Jabr, author of Becoming Earth: How Our Planet Came to Life
Planet Earth is estimated to be 4.54 billion years old—plus or minus about 50 million years. No one knows how life originated on our planet; many scientists, however, believe that microbes were one of the earliest, if not the earliest, life forms. In this week’s Germ Gem post, I discuss recent discoveries from “geomicrobiology”(at the intersection of geology and microbiology) and “geoarchaeology”(archeology with a geological bent)—multidisciplinary scientific fields that are providing new insights into the age-old question: when did life on Earth begin?
How is” life” defined? “Life” is defined as: “any system capable of performing functions such as eating, metabolizing, excreting, breathing, moving, growing, reproducing, and responding to external stimuli.” The Tree of Life—a phylogenetic tree—is a graphic tool that biologists use to portray evolutionary relationships among plants, animals, and other forms of life.
The idea of a Tree of Life can be traced to Charles Darwin, the English naturalist and father of the theory of evolution, and his 1859 publication of On the Origin of Species. Seven years later, German zoologist Ernst Haeckel drew a more comprehensive tree representing Earth’s wealth of species.
In 1977, University of Wisconsin microbiologist, Carl Woese, posited a modern day concept of the Tree of Life containing three major limbs called domains: Bacteria, Archaea, and Eukarya. New molecular biology techniques allowing the probing of every nook and cranny on Earth for DNA or RNA made this radically refurbished Tree possible.
Together with geological and paleontological data, the molecular evidence now suggests that life began when bacteria first appeared on Earth. (The “viruses first” controversy is still raging as to whether viruses—microscopic infectious microbes that can’t reproduce on their own and don’t have their own metabolism—are living members of the Tree and appeared before bacteria.) To this day, however, no one knows the origin of bacteria.
The search for a common ancestor. Charles Darwin argued that all existing creatures descended from a small number of progenitor species. Like Darwin, many modern day scientists continue the quest to find our common ancestors.
Scientists now working in fields such as geomicrobiology and geoarchaeology suggest that a life form dubbed the “last universal common ancestor” (LUCA) emerged on Earth about 4.2 billion years ago, a little earlier than previously thought. (See, “The Nature of the last universal common ancestor and its impact on the early Earth system,” Nature Ecology & Evolution, July 12, 2024). In their most recent studies, researcher also found that LUCA likely had 19 CRISPR genes, an apparatus modern bacteria rely on to chop up the genetic material of vial invaders. (See, “CRISPR: Everything You Wanted to Know But Were Afraid to Ask,” Germ Gems, November 11, 2019). If, indeed, LUCA was endowed with CRISPRS, this would suggest viruses emerged before bacteria, in support of the “viruses first” school of thought.
Origin of life. Modern day biologists are getting closer to answering the question of “when” life began on Earth. Nonetheless, the question of “how” life began on this planet remains a complete mystery. Darwin didn’t have an answer to this puzzling question and neither do any of our modern day geomicrobiologists or geoarchaelogists.
If you find this fact unsettling, I’m afraid you’ll have to look elsewhere than science for the answer, or—you’ll just have to live with it.
As a seeker, Dr. Peterson, this is a question I must ask myself every day...
Phil, your most provocative article, starting with, “Life” is defined as: “any system capable of performing functions such as eating, metabolizing, excreting, breathing, moving, growing, reproducing, and responding to external stimuli.” As a PhD student from a medical school, I had labs that used HeLa cells, the immortal cells from the cancer of a woman, Henrietta Lacks, who died from that cancer in the 1950s. By any definition of life, including yours, these cells are living and DNA analysis would clearly identify them as “human”. So they are human and they are living, but are they a living human being? Of course not, but every MD and PhD involved in medical research should read The Immortal Life of Henrietta Lacks,…