Sort by Creation Date - All Node Dates are "36 years, X weeks ago"

When I set a Full Mode block sorted by Creation Date, and set the block to display the Node Date, all the node dates are like "36 years, 19 weeks ago" (i.e. January 1970, like if a date field is set to zero, I think). The sorting is fine, it's just the Note Date display that seems botched. Sorting and display of modification dates display ok, though.