Hijack from Meteorites and Warm Little Ponds:

There are some who think that life origin of life on Earth, sprung from within Earth.

Here is one (most recent) from Naked Earth (subtitle: The New Geophysics), by Shawna Vogel, pages 179-180:
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According to [Carl] Woese's evolutionary tree, the most primary of the present-day bacteria lie within a group called the achaebacteria. All achaebacteria thrive in intense heat, and most derive their energy from breaking chemical bonds. The bacteria that inhabit the undersea hot springs fall into this group. Woese believes that these modern species evolved from a similar type of ancient bacteria that probably grew at temperatures near the boiling point of water and may have drawn its energy from the sulfurous compounds spewing out of hydrothermal vents. If that's true, the bacteria seen at vents today could be the closet descendant we know of the original forms of life on earth. That would imply that the earth's unique way of venting its heat had a tremendous impact on that dawning era when life was first gaining its toehold on the planet.

Even if sulfur-loving bacteria were the first creatures to appear on earth, though, this is still not the complete solution to the origin of life. "There's still left the question of how does all that information get into the first little cell," says [John] Corliss, who is now at the Goddard Space Flight Center in Maryland working on one aspect of this problem. How did life take the complicated step from a batch of chemicals in the prebiotic soup to an organized entity that could reproduce itself? That has proved to be the most difficult question for researchers to answer.

When we have fully explored our solar system, we might get an answer or, at least, a clue.

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I'm agnostic with respect to this theory and all others. I have thought, prior to reading this book, that one possibility is that life pervades the Universe and it is quite "cheap."