How Did Life Begin?
How life came from non-life is still largely a scientific mystery.
Structure of a variety of membrane proteins
Despite how much we know about the state of the Earth 3–4 billion years ago and the complexity of the building blocks of life—DNA, RNA, amino acids, sugars—no entirely plausible scientific explanation for the spontaneous origin of life has been found. How life came from non-life, or abiogenesis, is still largely a scientific mystery.
Because the topic does not have as many potentially useful applications as other areas of science, less research has been performed in this area. However, scientists are currently approaching this challenge from a number of different perspectives, and it is possible that broad consensus will emerge in the future.1
God could have created the first life through regular processes, or God could have done a miracle. In either case, BioLogos affirms that God is the creator and sustainer of all life, from the first life form to each of us. If consensus for a particular scientific explanation emerges, we will celebrate, because we will have more insight into God’s handiwork. Yet no matter how far science progresses, we can never exhaust the wonder and gratitude we feel for God’s good gift of life.
The first life on Earth
In discussions about the origin of life, an important first step is clarifying what is meant by life. The first forms of life on Earth were probably very different from what we would call life today. It may be tempting to think of life as anything containing the DNA double helix so familiar to us. However, the main property required for early life is self-replication. The earliest self-replicating systems could have been made out of DNA, RNA, or some other basic building blocks. The key feature of such systems would have to be the ability to gather chemicals from the local environment and make copies of themselves.
All life on Earth contains carbon as an essential elemental building block.2 Carbon is the simplest element capable of forming the remarkably complex molecules that are so prevalent in life forms. Therefore, it is likely that carbon was involved from the beginning. Compounds containing carbon are generally categorized as organic; and exploring the natural mechanisms that create complex organic compounds is a main focus in research on the origins of life.
The Earth is approximately 4.6 billion years old. All evidence suggests that the Earth was inhospitable to life for the first 700 million years, largely because it was so hot. However, the Earth gradually cooled, and 4 billion years ago it became more hospitable. Within little more than 100 million years, the first single-cell life forms appeared.3 Where did these organisms come from? And what were their capabilities?
Although we do not know the path that led to these early bacterial forms, it seems likely that DNA had emerged as the information molecule by this time. Microbiologist and physicist Carl R. Woese suggests there was a considerable amount of lateral gene transfer among the first forms of bacteria called archaebacteria.4 Lateral gene transfer, which is the movement of genes from one bacterium to another, would have enabled the exchange of genetic material, and it would therefore expedite the process of diversification of biological function acted upon by natural selection. How these first organisms ever developed in the first place is the topic of the following discussion.
The Miller-Urey experiment
Charles Darwin is often credited for the original “warm little pond” hypothesis, which proposes life may have formed from a combination of inorganic compounds and energy.5 Soviet biochemist Aleksandr Ivanovich Oparin revisited this idea and proposed life formed in an environment that lacked oxygen but was energized by sunlight.6 These kinds of ideas are the basis of much research of life’s origins, including the famous Miller-Urey experiment.
In 1953 at the University of Chicago, Stanley Miller and Harold Urey tackled the problem of the origin of life by reproducing the conditions they believed to be present on the primitive Earth when life originated. By zapping a mixture of water and inorganic compounds with electricity, they produced organic compounds including amino acids, the building blocks of protein.7 This result catalyzed further experiments—and at least to some, it appeared that the solution to life’s mystery was about to unfold.
A subsequent discovery by Joan Oro at the University of Houston, published in 1961, demonstrated that an essential component of DNA—adenine—as well as several amino acids could be formed by heating the inorganic compound hydrogen cyanide in water-ammonia.8 Though this work potentially contributed useful pieces to the puzzle,9 Miller-Urey type experiments have fallen short of providing a full answer to how life originated. It’s one thing to have organic compounds present, it’s quite another to have them form a self-replicating system.
Recently, these initial results were revisited with more sensitive methods. Researchers discovered additional amino acids and other building blocks formed during the Miller-Urey experiments that they originally had not realized.10 Miller continued a variety of experiments to pin down life’s origins and, though the mystery remained unsolved, members of his lab discovered amino acids and other building blocks for life can also form from inorganic compounds in extremely cold environments.11
How life came together
Explanations of how the amino acids, nucleotides, and sugars were formed, how they assembled in the form of DNA and RNA, and then how these building blocks of life came to replicate themselves and acquire the enzymes to facilitate this process, are all still speculative. Many interesting ideas are being researched, however, including the deep sea vent theory,12 radioactive beach theory13 and crystal or clay theory.14Another opinion, held by Francis Crick and others, is that the only explanation for life on Earth is that it came from another planet.15 However, this type of explanation only pushes the question farther back: How did this extraterrestrial life originate? A compelling scientific explanation of the origin of life here on Earth has not yet emerged.
Evolutionary theories of how life originated fall in two main camps: the gene first hypothesis and the metabolism first hypothesis. The gene first hypothesis currently focuses on RNA rather than DNA, as certain RNA molecules have shown the ability to function as enzymes, suggesting RNA could have both carried information and copied itself. From this point of view, RNA preceded both DNA and protein synthesis. On the other hand, the metabolism first hypothesis argues the molecules of prebiotic materials formed chemical cycles and networks of chemical reactions that gave rise to primitive metabolic systems. These metabolic systems existed before RNA and provided the environment for RNA replication to later emerge. Despite the exploration of numerous avenues of research, both theories currently lack conclusive evidence.
While researchers have recently generated self-replicating RNA from prebiotic molecules in the laboratory,16 it is difficult to understand how RNA—a notoriously unstable polymer—could have supported self-replicating systems in the hostile chemical and thermal environment of early planet Earth.
Regardless of how, it is clear that life did emerge, and the first life forms were single-celled organisms that began to replicate and diversify. The lack of scientific consensus on the origin of life does not diminish the strength of evolutionary theory, which only seeks to explain the diversity of life forms after life had already begun.
Although the origin of life is certainly a genuine scientific mystery, this is not the place for thoughtful people to wager their faith. All that has happened in the history of life has happened according to God’s sovereign purposes, and Christ “is before all things, and in him all things hold together” (Col. 1:17).
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Jeff Hardin | Science & Wonder