Origin of Life: Earth's Early Atmosphere Wasn't Reducing`
The standard assumption in origin of life research has been that the primordial earth had a reducing atmosphere, which favors prebiotic chemistry. Although more recent studies have suggested this assumption might not be true, a Nature study now directly shows that the earth did not have a reducing atmosphere up to 4.35 billion years ago—even before the beginning of the late heavy bombardment and the first evidence for the origin of life. The new study also explains why there is no evidence for a prebiotic soup (non-biologic carbon deposits) in the earth's earliest rocks.
Early history of the earth
Radiometric dating of meteorites have demonstrated that the Solar System (including the Sun, earth, and other planets) formed 4.55 billion years ago. Originally, all solar system bodies would have possessed atmospheres dominated by hydrogen and helium (similar to the composition of the Sun).
However, the earth was struck early in its history by a Mars-sized planet, which blew off much of its primordial atmosphere. So, the original thick atmosphere was replaced by a much thinner atmosphere, dominated by gasses produced through volcanic eruptions.
Scientists have known for some time that these gasses are primarily composed of water, carbon dioxide, and sulfur dioxide. However, origin of life models required the presence of reducing atmospheres in order for prebiotic chemistry to occur. Without reducing conditions, prebiotic organic building blocks are not formed. So scientists were reluctant to write off reducing atmospheres for planet earth until recently.
Although no rock formations have survived intact prior to 3.9 billion years ago, the earth's earliest crystals, zircons have been found to date as far back as 4.4 billion years ago, only a few hundred million years after the earth's formation. Since these crystals are formed in the presence of water, the initial evidence showed that the earth was much cooler than originally thought.
However, the surface of the earth was nearly completely destroyed during the Late Heavy Bombardment, from 4-1 to 3.9 billion years ago. Because of the energy produced by these large collisions, the surface of the earth did not resolidify until nearly 3.85 billion years ago.
Small zircons survived this period, providing a glimpse into the earth's early history. Besides indicating the presence of water, these early zircons allow scientists to examine the oxidation of minerals within the crystals to help determine that probable oxidation state of earth's early atmosphere.
The rare earth metal cerium can exist in two oxidation forms. By measuring the prevalence of the two forms (the Ce4+/Ce3+ ratio) in zircons, scientists can determine the relative oxidation conditions under which the crystals formed. However, in order to calibrate the system, scientists had to produce zircons artificially under differing oxidative conditions to measure the Ce4+/Ce3+ ratio.
The scientists then compared these values to those found in ancient zircons formed in the earth's mantle and those recovered from the moon. As expected, the lunar samples expressed a low cerium ratio, since they would have formed in the absence of oxidative conditions. However, the cerium ratios of earth's ancient zircons were ten-fold higher. By dating their sampling of zircons and comparing the cerium ratios, the scientists determined that the earth's mantle had reached its current oxidation state 4.3 billion years ago—a full 500 million years before the evidence for the first appearance of life.
According to Bruce Watson, Professor of Science at Rensselaer Institute, "We can now say with some certainty that many scientists studying the origins of life on Earth simply picked the wrong atmosphere."
Implications for origin of life
Origin of life researchers had speculated that the earth had a reducing atmosphere for hundreds of millions of years before life originated. Under this scenario, organic molecules combined together to form the building blocks of life, forming a "prebiotic soup."
However, for a number of years the theory has been in trouble, since all ancient deposits of carbon exhibit 13C/12C ratios indicating that the carbon originated from living organisms, instead of some non-living "prebiotic soup." So, there is no evidence for the existence of any kind of pre-biotic soup.
The new study tells us why no prebiotic soup existed. The earth's atmosphere was oxidative as early as 4.3 billion years ago, preventing prebiotic chemistry from occurring. Although small local areas scattered over the earth might be reducing over short periods of time, the new data effectively shuts down the idea that the earth was a factory for the generation of prebiotic building blocks.
How do origin of life researchers explain where the building blocks of life came from? The author of the article, in an interview suggested that the building blocks for life were not created on Earth, but delivered from elsewhere in the galaxy.
However, since the earth suffered through the Late Heavy Bombardment from 4.1 to 3.9 billion years ago (during which time prebiotics would have been destroyed) and life originated almost immediately afterward, this would have left very little time for any kind of prebiotics to accumulate on earth. The non-reducing hostile conditions would still thwart self-assembly of the meager prebiotics that might have accumulated during that short period of time.
Evidence that the earth's primordial atmosphere was oxidative rather than reducing as early as 4.3 billion years ago has dealt a knockout blow to naturalistic origin of life theories. Since prebiotic chemistry cannot synthesize the building blocks of life under oxidative conditions, scientists are left with the reality that naturalistic origin of life theories cannot explain the origin of life on earth.
Ever hopeful of increasingly unlikely scenarios, scientists are now trying to say that prebiotics were delivered from outer space, although such prebiotics would have been incinerated during the late heavy bombardment.
We wouldn't be surprised if panspermia or seeding of life on earth by aliens became the reigning "scientific" paradigm offered by naturalistic scientists. The obvious, and much more reasonable hypothesis that God created life on earth, will be avoided at all costs.