14 DAY TRIAL // Experts proposed back in 2010 that the faint young Sun paradox had finally been solved. However, studies conducted this year indicate the paradox to be pretty much in place. As such, an explanation for it is still needed and sought for.
The paradox refers to the contradictions that develop between theories explaining how the Sun evolved, versus studies showing how our own planet developed to its present form. The two sets of theories cannot be reconciled in any manner, it would seem.
Scientists know now that our parent star is about 4.6 billion years old, while Earth is slightly younger. Studies conducted here have demonstrated that liquid water began flowing on our planet's surface as early as 700 million years after the planet formed.
The problem this presents is that the Sun was considerably dimmer than it is today. In fact, astronomers say, the star produced 30 percent less energy than current level. This further implies that its habitable zone was not located where Earth's orbit is.
As such, only ice may have endured on the surface of the planet, whereas the presence of liquid water was impossible. In all likelihood, the Sun's habitable zone was closer to Venus than Earth. Yet, the fact remains that liquid water did run on the planet. The question is, how was that possible?
An obvious explanation, and one that was proposed from the get-go, was that Earth had more carbon in the atmosphere, which contributed to a greenhouse gas effect that warmed the planet. Another solution was that the planet had a lower albedo.
What the 2010 study found out was that the chemical composition of rocks dating from the early Earth does no support the idea that methane- or carbon dioxide-induced global warming was running wild.
The second explanation, that the planet had a lower albedo, must therefore be true, that team said when proposing that the paradox had been solved in a paper published in the top scientific journal Nature.
However, the controversy was only laid to rest for a year. Now, NASA Ames Research Center (ARC) scientist Colin Goldlatt and Kevin Zahnle say that the reduced albedo couldn't – even under the most optimistic of scenarios – have warmed the planet sufficiently to allow for liquid water to form.
“We show that, even with the strongest plausible assumptions, reducing cloud and surface albedos falls short by a factor of two of resolving the paradox,” Goldlatt and Zahnle say, quoted by Technology Review.
With the new study, the team conclusively proved that neither albedo or greenhouse gases could have warmed Earth some 3.8 billion years ago. If they didn't do it, then what did?