Meteorites carried life's building blocks to Earth

A new analysis of carbon meteorites suggests that they likely carried some of the building blocks needed for DNA to the Earth, according to a NASA-funded study published on Monday.The research in the Proceedings of the National Academy of Sciences adds weight to the long-debated theory that at least some of the materials needed to make early life forms came to our planet via meteorites.Scientists used advanced mass spectrometry instruments to scan 11 organic-rich meteorites called carbonaceous chondrites for nucleobases, which contribute to making DNA and RNA. They found three nucleobases -- purine, 6,8-diaminopurine and 2,6-diaminopurine -- that "are widely distributed in carbonaceous chondrites" and which are "rare or absent in terrestrial biology," said the study.Scientists found no significant concentrations of the trio in soil and ice samples near where the meteorites landed, the study said."Finding nucleobase compounds not typically found in Earth's biochemistry strongly supports an extraterrestrial origin," said Jim Cleaves, one of the study's authors from the Carnegie Institute of Washington's Geophysical Laboratory."This shows us that meteorites may have been molecular tool kits, which provided the essential building blocks for life on Earth," Cleaves said.Previous studies have shown that some meteorites contain nucleobases but that they shared traits with those already on Earth, fueling debate over whether the meteorites carried these elements or were contaminated on impact.Earlier this year, NASA distanced itself from a space agency employee's claim that he had sliced open several types of carbonaceous chondrite meteorites and found evidence of alien bacteria fossils inside.