Genetic Code Indicates that Life Did Not Originate at High Temperatures
My father—who was from India—loved hot, spicy foods. In fact, he was quite proud of his ability to eat food that would have the average person desperately reaching for a pitcher of water. The food people eat is a big part of their culture. You can tell a lot about a person’s heritage from the foods they like to eat.
A team of origin-of-life researchers recently used this idea, of sorts, to gain understanding about the heritage of the first life-forms on Earth. Instead of relying on diet, however, these scientists examined the biochemical makeup of currently existing organisms to determine if the first life-forms originated in the sizzling, hot environment of the primordial Earth.
The consequences of this study are profound. The new insight gained from this work frustrates attempts by origin-of-life researchers to sidestep serious problems associated with the standard evolutionary approach to life’s beginnings.
Difficulties Facing the Origin-of-Life Paradigm
As described in the book I wrote with Hugh Ross, Origins of Life, advances taking place in origin-of-life research during the last decade make it difficult to conclude that life could emerge from nonlife strictly through physical and chemical means.
1.Life first appears remarkably early in Earth’s history. Geochemical evidence indicates life was likely present on the Earth at 3.86 billion years ago. The oldest rocks date at 3.9 billion years ago. Prior to this time, the Earth existed largely in a molten state, unsuitable for life. Between 4.5 billion years ago and about 3.5 billion years ago, the Earth experienced numerous impact events that sterilized the surface. These impacts melted rock and volatilized the Earth’s oceans.
2.The geochemical and fossil records also indicate that the first life on Earth was chemically complex.
3.Many origin-of-life researchers begrudgingly acknowledge that the early Earth’s conditions were not as conducive to the formation of prebiotic molecules as they would like.
4.Consistent with this admission, the geochemical record yields no evidence for a prebiotic soup.
Taken together, these observations unequivocally indicate that as soon as the Earth could even remotely support life, chemically complex life appeared—in the absence of a prebiotic soup! Life emerges under conditions in which it should not have originated, let alone persisted; that is, hostile ones.
Thermophiles to the Rescue
The discovery of archaea and eubacteria thriving in hostile, high-temperature environments suggests to some origin-of-life researchers that life arose under the extreme conditions of the early Earth prior to 3.9 billion years ago. This scenario seemingly provides a loophole to keep the naturalistic explanation for life’s origin viable. Origin-of-life researchers suggest that thermophiles evolved first and gave rise to mesophiles.
Any life emerging on the Earth’s surface prior to 3.9 billion years ago would have needed a high-temperature start. Origin-of-life investigators hope to extend the time available for life’s start by pushing origin-of-life events beyond 3.9 billion years to a time when the Earth’s environment was hot. A thermophilic origin of life presumably provides the additional time required for natural processes to generate life.
The thermophilic origin-of-life scenarios garner support, say its proponents, from evolutionary analysis of DNA sequences. This work places these heat lovers at the base of the evolutionary tree of life. Thermophiles seem to be the oldest and most primitive organisms on Earth. Laboratory experiments simulating a hot, chemically harsh early Earth environment, and modeled after deep-sea hydrothermal vents indicate that amino acids, peptides, and other biologically interesting molecules might form under harsh conditions. These reactions represent necessary early steps in a thermophilic origin-of-life pathway.
The Genetic Code and the Origin of Life
Even though there seems to be support for a high-temperature origin of life, a number of problems exist for this scenario. For a detailed discussion of some of these problems see Origins of Life.
Add to the list of problems the structure of the genetic code. The genetic code is the set of rules that the cell’s biochemical machinery uses to convert the information stored in DNA into proteins through the process of translation.
Based on recent analyses it appears that the rules of the genetic code have been carefully fine-tuned to minimize the harmful effects of substitution mutations. While this type of optimization denotes the work of an intelligent agent, evolutionary biologists maintain that the optimized genetic code evolved under selective pressures.
Researchers from Cornell University and the University of Waterloo reasoned—from an evolutionary standpoint—that if life originated under high temperatures, the selective pressures that perfected the genetic code should also have optimized it to withstand high temperatures. In other words, the rules of the genetic code should reflect life’s hot heritage, if it emerged under high-temperature conditions.
These researchers concluded, however, that the genetic code reveals no indication that it is ideally suited for a high-temperature environment. From an evolutionary perspective, the genetic code must have arisen under moderate, mesophilic conditions. Based on this result, it’s reasonable to conclude that life also arose under mild conditions as well.
This study makes it less tenable to extend the time available for the origin of life beyond 3.9 billion years ago and also undermines the notion that life emerged from hydrothermal vents.
Early earth was too hot for the first life-forms to handle.