How Life Came to Earth

Or rather, how the precursor molecules definitely did - and do. This source arrived in Murchison, Australia on September 28th, 1969.

From Extraterrestrial nucleobases in the Murchison meteorite :

Carbon-rich meteorites, carbonaceous chondrites, contain many biologically relevant organic molecules and delivered prebiotic material to the young Earth. We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ¹³C = + 44.5‰ and + 37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These new results demonstrate that organic compounds, which are components of the genetic code in modern biochemistry, were already present in the early solar system and may have played a key role in life's origin.

It has been known for some time that the precursors of DNA have been found in meteorites, but the possibility existed that they were just contamination from terrestrial sources hadn't been totally excluded - before now.

Examination of the precursors now shows that the ratio of isotopes of carbon in them isn't in the right ratio for the usual C¹² or the rarer C¹⁴ isotopes found on Earth. The ratio contains far too much of the C¹³ isotope that's in the meteorites themselves. So the precursors of Life had to have been formed "out there" and brought here.

More on the subject in previous posts here, here, and here. The weakest form of the Panspermia hypothesis is now proven.