14 DAY TRIAL // It could be that our planet has a lot more in common with Saturn's largest moon Titan than experts first thought possible. In a new investigation, carried out by experts at the University of Colorado in Boulder (UCB), it was revealed that the thick haze which constituted Earth's primordial atmosphere was most likely extremely similar to the one currently enveloping the gas giant's natural satellite. The conclusions may yield new insights into the chances of life existing on Titan, and may also give us a better idea of how our own planet looked like just after it solidified, SpaceRef reports.
One of the main roles that the early haze may have played on Earth was protecting early life. At the time, billions of years ago, the Sun was a lot cooler than it is today, and it also emitted vast amounts of ultraviolet radiation. These photons are very harmful to living creatures, as evidenced by the fact that, even now, prolonged exposure to sunlight can cause mutations in the skin, and also skin cancer. It may be that the thick layer of clouds that covered our planet may have protected the earliest and most sensitive life forms from the damaging effects of UV light, allowing more complex life to become possible.
“Since climate models show early Earth could not have been warmed by atmospheric carbon dioxide alone because of its low levels, other greenhouse gases must have been involved. We think the most logical explanation is methane, which may have been pumped into the atmosphere by early life that was metabolizing it,” explains the lead author of the new investigation, UCB doctoral student Eric Wolf. He adds that this is precisely what's currently going on on Titan, where lakes of liquid methane and ethane (as well as other hydrocarbons) exist at both the north and the south poles. The scientist says that our early atmosphere may have also included large concentrations of chemicals such as ammonia.
The UCB group now proposes in a new paper that methane was the gas responsible for the emergence of life on Earth. “The UV shielding methane haze over early Earth we are suggesting not only would have protected Earth's surface, it would have protected the atmospheric gases below it – including the powerful greenhouse gas, ammonia – that would have played a significant role in keeping the early Earth warm,” Wolf explains, adding that as much as 100 million tons of haze may have been produced annually in the early atmosphere. He argues that this happened during the Achean Period, 3.8 to 2.5 billion years ago.
“If this was the case, an early Earth atmosphere literally would have been dripping organic material into the oceans, providing manna from heaven for the earliest life to sustain itself. Methane is the key to make this climate model run, so one of our goals now is to pin down where and how it originated,” adds UCB Atmospheric and Oceanic Sciences Department professor Brian Toon. Details of the work appear in the June 4 issue of the top journal Science. Funds for the work came from the NASA Planetary Atmosphere Program.