Preserved poop can reveal much about the ancient world. It can hold the DNA of the animal that deposited it, bits of undigested plants and pollen, and now it can even reveal the average rainfall the year of the pooping.
The best place to find ancient poop is in middens, which are basically communal toilets shared by families of rodents. The poop is preserved in these middens because the ancient rodent urine crystallized around them, cementing them together and saving them for future ecologists to study. Although a lot of the analysis on rodent middens are fairly involved, a new analysis is so simple and straightforward that anyone can do it - as long as you don't mind rooting through ancient rodent shit, of course.
Claudio Latorre Hidalgo, a paleoecologist at Santiago's Pontifical Catholic University of Chile, says just the size of the fecal pellets can tell us a lot about the ancient world. The bigger the poop, the bigger the rodent that deposited it, and that means that the climate must have been lusher in order to support relatively larger animals. In other words, the size of the poop can tell us just how much it rained when the animal deposited it.
The research team went to Chile's Atacama Desert, one of the driest regions in the world, to study nine middens left behind by ancient chinchillas. They measured all the pellets in the middens, then focused on just the biggest 20% to ensure they were only focusing on those left by the biggest adult chinchillas. They then carbon-dated the poops and checked them against existing measures of ancient rainfall, and the poop sizes proved a perfect match.
That means that, in the absence of more traditional clues to ancient rainfall, such as sediment cores from lakebeds, the answer may lie at the bottom of an ancient rat toilet.