Evolution of Photosynthesis: A Theory in Crisis
“Although the last word on the origins of oxygen-making photosynthesis isn’t in,” writes Mitch Leslie in Science,1 “researchers say they are making progress. One thing is for certain, however: Without this innovation, Earth would look a lot like Mars.” That’s the end of his story. What did he say in the beginning and middle? Not much, in terms of scientific evidence.
Leslie started by singing the praises of photosynthesis. Maybe this excerpt will help you see the world in a new light:
Try to picture the world without photosynthesis. Obviously, you’d have to strip away the greenery–not just the redwoods and sunflowers, but also the humble algae and the light-capturing bacteria that nourish many of the world’s ecosystems. Gone, too, would be everything that depends on photosynthetic organisms, directly or indirectly, for sustenance–from leaf-munching beetles to meat-eating lions. Even corals, which play host to algal partners, would lose their main food source.
Photosynthesis makes Earth congenial for life in other ways, too. Early photosynthesizers pumped up atmospheric oxygen concentrations, making way for complex multicellular life, including us. And water-dwellers were able to colonize the land only because the oxygen helped create the ozone layer that shields against the sun’s ultraviolet radiation. Oxygen-producing, or oxygenic, photosynthesis “was the last of the great inventions of microbial metabolism, and it changed the planetary environment forever,” says geobiologist Paul Falkowski of Rutgers University in New Brunswick, New Jersey.
This being the reality, coming up with a story of how photosynthesis evolved is a challenge. “Given its importance in making and keeping Earth lush, photosynthesis ranks high on the top-10 list of evolutionary milestones.” One looks in vain, though, for evidence that it evolved at all. Leslie approaches the story from two fronts: geology and biochemistry. Let’s examine the latter first.
The machinery involved in photosynthesis is mind-boggling. Electrons are shuttled between two reaction centers called Photosystem I and Photosystem II. “Light jump-starts an electrical circuit in which electrons flow from the photosystems through protein chains that make the energy-rich molecules ATP and NADPH,” he said in a brief simplification. “These molecules then power the synthesis of the sugars that organisms depend on to grow and multiply.”
The cyanobacteria that live in hot springs can use hydrogen sulfide instead of other oxygen-hugging molecules like water for an energy source. Leslie described these nonconformists, which don’t produce oxygen, as simpler: “Their photosynthetic proteins huddle in relatively simple ‘reaction centers’ that may have been the predecessors of the two photosystems.” But in the very next sentence he said, “Envisioning the steps that led to this complex biochemistry is mind-boggling.”
All he could suggest in terms of an evolutionary story were two scenarios: (1) bacteria co-opted existing machinery used for other functions; and (2) bacteria shared their technology by lateral gene transfer. Tantalizing as these suggestions are, he admitted scientists are at a loss. “However, other researchers remain skeptical, arguing that one photosystem evolved from the other, possibly through the duplication of genes, creating an ancient cell with both. No one knows for sure.” As if to fiddle over a grave, he threw in another complication: “Either way, it took some fancy fiddling to convert the primitive reaction centers to oxygen-generating photosystems.” So not only are evolutionists at a loss to explain the anoxic photosynthesis machinery, it is no small order to upgrade it to the advanced kind.
Turning to geology, evolutionists try to approach the question by looking for clues when oxygen first became abundant in the early earth. That, at least, might pinpoint the time that oxygenic photosynthesis began:
How the photosystems got their start is crucial for understanding the origin of photosynthesis. But the question that’s drawn the most attention–and provoked the most wrangling–is when photosynthesis began. “Most researchers accept that nonoxygenic photosynthesis arose first, probably shortly after life originated more than 3.8 billion years ago. “Life needs an energy source, and the sun is the only ubiquitous and reliable energy source,” says Blankenship.
The common story is that there was a “great oxidation event” at 2.4 billion years ago. This is supposed to mark the onset of oxygenic photosynthesis—the time eukaryotes figured out the more demanding photosynthesis that swipes electrons from water, generating oxygen as a by-product. Leslie entertained controversial evidence that oxygenic photosynthesis began even earlier. That was the occasion for the reference to Mars:
The early-origin case isn’t ironclad. For example, a 2008 paper that has some researchers fuming claims that the oil biomarkers are contaminants that seeped in from younger rocks. Advocates also have to explain why it took hundreds of millions of years for oxygen to build up in the air.
Although the last word on the origins of oxygen-making photosynthesis isn’t in, researchers say they are making progress. One thing is for certain, however: Without this innovation, Earth would look a lot like Mars.
What would he think, then, about a new report that pushes oxygen back another billion years? That would not only push the origin of the complex machinery of photosynthesis further back in time, providing less time for the lucky accidents to happen; it also cast doubt on the origin of life itself, because the prebiotic molecules the astrobiologists envision cannot form in the presence of oxygen. Leslie entertained the possibility of an earlier date in a March 13 entry in Origins, the AAAS blog celebrating the Darwin Bicentennial. “It’s no surprise that this is a tough question to answer,” he cautioned. But then, Phil Berardelli reported on Science Now2 March 16 that researches deduced the presence of oxygen in iron-oxide-rich rocks in Australia containing red hematite said to be 3.46 billion years old:
If confirmed, the discovery could mean that oxygen-producing photosynthetic organisms originated more than a billion years earlier than previously thought….
It’s “very compelling evidence,” says isotope chemist Paul Knauth of Arizona State University, Tempe. The result may go “against the widespread view that [oxygenic] photosynthesis didn’t appear” until about 2.4 billion years ago, he says, but the paper’s conclusion “is the simplest explanation.” He says he hopes the findings will provoke discussion among “all those who argue that the case is closed–surely, we are still learning.”
1. Mitch Leslie, “Origins: On the Origin of Photosynthesis,” Science, 6 March 2009: Vol. 323. no. 5919, pp. 1286-1287, DOI: 10.1126/science.323.5919.1286.
2. Phil Berardelli, “Oxygenated Oceans Go Way, Way Back,” ScienceNOW Daily News, 16 March 2009.
Always learning, yet never able to come to the knowledge of the truth (Paul). Picture transients on the street trying to build a power plant. Even if they co-opted pieces of their cardboard shacks, and shared their technology by lateral jeans transfer, any success would still be due to intelligent design. Evolutionists expect us to believe one of the most efficient and complex examples of cellular technology of all (07/27/2007, 05/09/2007) just emerged out of nowhere – right near the beginning of life on earth, along with all the other cellular technologies and coding systems. If scientists these days did not feel obligated to force-fit every thought into a 19th-century speculative plot, such evidence-free flights of imagination would be laughable.