Here’s a head-scratcher for you: In August, sheep in Massachusetts will begin drinking water from the Beartooth Mountains as part of an experiment to better understand the record of climate change preserved in fossilized teeth.
Daniel Green, a graduate student in the Department of Human Evolutionary Biology at Harvard University, was getting help Thursday from the Beartooth Ranger District to fill 13 55-gallon barrels with water from the West Fork of Rock Creek. The water was to be shipped by United Parcel Service back to Cambridge, Mass., on Friday, where it will be used to water two Dorsett sheep for a year and six other sheep for three weeks.
Here’s the science behind the project. Oxygen, one of the atoms found in a water molecule, is made up of eight protons and a variable number of neutrons. Light oxygen has only eight neutrons. Heavy oxygen has 10.
A scientist in Utah has made maps of water weights around the world, and it just so happens that the Beartooth Mountains have some of the lightest water on average in the lower 48 states. That’s what prompted Green to fly to Billings, purchase 13 plastic barrels, and drive a U-Haul truck loaded with the barrels up the dusty, winding West Fork road.
The reason the Beartooths have what’s called “isotopically depleted water” is that by the time rain or snow falls in the mountains, far from the Pacific Ocean, most of the heavier water molecules have already fallen to the ground.
What does all of this have to do with fossils?
Teeth are some of the hardest bone in animals, so they are often found preserved as fossils. By taking samples from fossilized teeth, scientists get a picture of the climate at the time the animal lived because in the teeth are records of the oxygen molecules ingested by the animals when they drank water. From the presence of the oxygen the scientists can make inferences because light water, the type with fewer neutrons, evaporates more quickly than heavy water. Heavy water condenses more readily. Rain and snow is formed when the air cools and condenses.
Thus, animals with a lot of heavy oxygen isotopes fossilized in their teeth lived during a wetter climate. Animals with lots of lighter oxygen isotopes in their fossilized teeth lived during a period of warmer weather.
“The point is to be able to reconstruct ancient climates and specifically rainfall patterns,” Green said.
Although scientists already sample fossilized teeth for the oxygen isotopes to understand climate at the time the animal lived, Green said scientists never have studied how quickly changes in the climate may be reflected in an animal’s teeth.
By having six sheep drink the Beartooth water for only three weeks, and then allowing two others to drink it exclusively for a year, Green is hoping to see how their blood and teeth respond to the different water weights. Four sheep will drink heavier Massachusetts water as a comparison group.
“We can see how fast the bodies of these animals reach an equilibrium with the water,” he said.
Forest Service firefighters Drew Brown and Ben Wagner weren’t involved in the science behind Green’s experiment, but they were happy to have the opportunity to fill Green’s barrels as a training exercise on portable pump setup and operation. With a 1½-inch hose in the creek, the pump could boost enough water to fill the 13 barrels in about 20 minutes.
“It’s surprisingly strong,” Brown said. “It will push water quite a ways.”
Green said the agency has been very supportive in fulfilling his experiment’s requirements for light water.
“The Forest Service in general has been really helpful,” he said.