Funny coincidence-- a few days after a COPV (fuel tank) dropped from space onto Brazil, a story has surfaced that looks like exactly the same kind of object was found in Australia last year (there is a picture with the article, too). The article claims (without cites) that it is from a US rocket launched in 1998. I'm not sure how they know that precisely, but I suppose the ground tracks of known re-entries narrowed it down. The tank was discovered in November, and the farmer who found it just started looking into the mystery, which is why the story popped up now.