News0 min ago
Answers
Best Answer
No best answer has yet been selected by K-Rabbit. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.Scientists aren't sure, but read here for latest theory:
http://pubs.usgs.gov/gip/dynamic/unanswered.ht ml
http://pubs.usgs.gov/gip/dynamic/unanswered.ht ml