Wild chinchillas tend to excrete their body wastes in personal piles called "middens". In the dry climate of the Atacama Desert in South America, these piles can be preserved for thousands of years. Scientists have discovered that they can use these preserved middens to gather information about rainfall in the distant past:
Link via Digg | Photo by Flickr user Arkangel used under Creative Commons license
By measuring pellet size in middens deposited in modern times when rainfall records exist, the team determined the relationship between chinchilla pellet size and amount of rain.
They then used this relationship to estimate how much rain fell at points throughout the past 14,000 years, by measuring and radiocarbon dating the animals' poop.
The results show increases in rainfall at 11- to 13.8-thousand years ago, and again about one- to two-thousand years ago.
Link via Digg | Photo by Flickr user Arkangel used under Creative Commons license
Their whole premise relies on Chinchillas (or more specifically, their poop habits/composition/relation to environmental water) not changing over the course of 14,000 years.