A community of the bacteria Candidatus Desulforudis audaxviator has been discovered 2.8 kilometres beneath the surface of the Earth in fluid-filled cracks of the Mponeng goldmine in South Africa. Its 60C home is completely isolated from the rest of the world, and devoid of light and oxygen. … 

99.9% of the DNA [there] belonged to one bacterium, a new species. The remaining DNA was contamination from the mine and the laboratory. …  A community of a single species is almost unheard of in the microbial world. … Deep-sea vent communities, for instance … use oxygen … produced by photosynthesising plankton at the surface. ….

D. audaxviator gets its energy from the radioactive decay of uranium in the surrounding rocks. It has genes to extract carbon from dissolved carbon dioxide and other genes to fix nitrogen, which comes from the surrounding rocks. … D. audaxviator has genes to produce all the amino acids it needs.  D. audaxviator can also protect itself from environmental hazards by forming endospores – tough shells that protect its DNA and RNA from drying out, toxic chemicals and from starvation. It has a flagellum to help it navigate.

That is New Scientist; here is Science.  This news does it for me; much more likely likely than not, life on Earth came from life elsewhere. 

Added: If life starts only on planets, the chance Earth life started on Earth is roughly the inverse of average number of planets seeded by each life origin.  If not, the chance is lower.  Here is more from Science:

[It] is prominent in small subunit rRNA gene clone libraries from almost all fracture fluids sampled to date from depths greater than 1.5 km across the Witwatersrand basin (covering 150 km by 300 km near Johannesburg, South Africa) … Severe nutrient limitation is believed to result in cell doubling times ranging from 100s to 1000s of years … Heterogeneity in the population … was quite low … suggesting a recent selective sweep or other population bottleneck. … We could not rule out the presence of organisms that might adhere to the surfaces of the fracture or that were smaller than the 0.2um filter pore … [It] appears capable of sensing nutrients in its environment.