My own private thesis is that it was mined early in the history of the Solar System as a source of carbonates, phosphates and sulfides for use by a now distant spacefaring civilization.
They used Venus' moon (now the planet Mercury) as a source of orbital energy to catapult the "goodies" out to the vicinity of Venus. Eventually Mercury lost so much energy it dropped into an orbit closer to the Sun and was of no more use.
Then they turned to Earth (or maybe did it at the same time), and used the Moon. It lost energy and receded from the Earth.
The space elevator systems used by the miners were built from local materials, e.g. hydrocarbons from Saturn's moon Titan. Billions of years after they were abandoned they finally fell to Earth along the Equator or evaporated into Venus' atmosphere.
The "sling shot" devices on both Mercury and the Moon rested on a pivot point constructed at what were, at the time, the Southernmost pole of each body. Mercury has "tilted" so the pivot point has moved from that position. Earth's Moon hasn't budged a bit and the hole for the pivot is right there at the Southpole ~ it's the deepest crater in the Solar System and may well have some sort of semi-solid lubricant left at the bottom.
The hydrocarbon space elevators on Earth fell to the location of the Equator about 600,000,000 years ago and today make up serious hydrocarbon deposits ~ some shale deposits involve secondary deposition of earlier liquid oil of course.
Whereas there's absolutely no evidence at all for Venus having popped out of Jupiter, there is at least the pivot point on Mercury (at http://a52.g.akamaitech.net/f/52/827/1d/www.space.com/images/080130-mercury-spider-02.jpg ) and the pivot point on the Moon (at http://tbn0.google.com/images?q=tbn:3a3hVF4KrMrPOM:http://nssdc.gsfc.nasa.gov ) to consider.
If Velikovsky had the sort of photographic material we have today he wouldn't have made that mistake with Venus Fur Shur.
</sarc> off, eh?