Swirling with lunacy and paranoia, the theories warn of mayhem and cataclysm. They fill books and websites, inspiring hand-wringing among gullible people. The claim: The world is ending Friday, the final chapter in an ancient Mayan prophecy carved into stone calendars thousands of years ago.

The stories are a jumble, based on everything from New Age mysticism to biblical "end times." In some accounts, a giant secret planet is about to slam into Earth, or a solar storm will wipe out the human race.

Dr. David Morrison is the NASA senior scientist leading the charge to debunk claims that the world is ending on Dec. 21, 2012 because of the Mayan
Dr. David Morrison is the NASA senior scientist leading the charge to debunk claims that the world is ending on Dec. 21, 2012 because of the Mayan calendar. (LiPo Ching/Staff).
None has any basis in fact, scientists say, but a poll in the summer found 12 percent of Americans are worried. Some teenagers have even talked of suicide. | » How would you spend your last days on Earth?

As Dec. 21, 2012, nears, however, the U.S. government has a secret weapon to hold back the tidal wave of misinformation and pseudoscientific quackery: a bespectacled 72-year-old scientist, often clad in a rumpled cardigan, sitting in a two-story office building off Highway 101 in Mountain View. | » Doomsday survival kit

David Morrison is Kryptonite for the world's conspiracy craziness. A Harvard University-trained astrophysicist who studied under Carl Sagan, Morrison is the senior scientist at the Astrobiology Institute at NASA Ames Research Center. He has worked on many of America's top space missions, from Mariner to Voyager to Galileo, and published more than 155 technical papers and a dozen books on astronomy. |

Tourists get their picture taken next to a slab of stone counting down the days until Dec. 21, 2012 at the Xcaret theme park in Playa del Carmen, Mexico,
Tourists get their picture taken next to a slab of stone counting down the days until Dec. 21, 2012 at the Xcaret theme park in Playa del Carmen, Mexico, Saturday, Dec. 15, 2012. (AP Photo/Israel Leal)