Life on Earth began after meteorites splashed into warm little ponds and leached them with essential elements between 3.7 and 4.5 billion years ago, scientists say. Calculations suggest that wet and dry cycles bonded basic molecular building blocks in the ponds' nutrient-rich broth into self-replicating RNA molecules that constituted the first genetic code for life on the planet. Researchers from McMaster University in Canada and Max Planck Institute in Germany based their conclusion on exhaustive research and calculations drawing in aspects of astrophysics, geology, chemistry, biology and other disciplines.
Available evidence suggests that life began when the Earth was still taking shape, with continents emerging from the oceans, meteorites pelting the planet - including those bearing the building blocks of life - and no protective ozone to filter the Sun's ultraviolet rays. "Because there are so many inputs from so many different fields, it is kind of amazing that it all hangs together," said Ralph Pudritz, from McMaster University. "Each step led very naturally to the next. To have them all lead to a clear picture, in the end, is saying there's something right about this," said Pudritz. "In order to understand the origin of life, we need to understand Earth as it was billions of years ago. As our study shows, astronomy provides a vital part of the answer," said Thomas Henning, from the Max Planck Institute for Astronomy.
"The details of how our solar system formed have direct consequences for the origin of life on Earth," said Henning. The spark of life was the creation of RNA polymers: the essential components of nucleotides, delivered by meteorites, reaching sufficient concentrations in pond water and bonding together as water levels fell and rose through cycles of precipitation, evaporation and drainage. The combination of wet and dry conditions was necessary for bonding, researchers said.
In some cases, favourable conditions saw some of those chains fold over and spontaneously replicate themselves by drawing other nucleotides from their environment, fulfilling one condition for the definition of life. Those polymers were imperfect, capable of improving through Darwinian evolution, fulfilling the other condition. That rudimentary form of life would give rise to the eventual development of DNA, the genetic blueprint of higher forms of life, which would evolve much later. The world would have been inhabited only by RNA-based life until DNA evolved. "DNA is too complex to have been the first aspect of life to emerge. It had to start with something else, and that is RNA," Pudritz said.
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