Today we’re looking for live snails so that we can measure how much carbon-14 they are incorporating into their calcite shells. Carbon-14 is a rare isotope of carbon that decays radioactively–organisms incorporate carbon-14 into their tissues and shells while they are alive, and as soon as they die, the carbon-14 starts decaying away. We can estimate how much carbon-14 there should have been in a shell, for instance, when the organism died, and we can measure how much is left: the difference tells us how long the shell has had to decay its carbon-14 away. Different organisms incorporate carbon differently, though, and it’s useful to get a modern sample (e.g. one that is alive, using carbon, when we find it) to compare to the older samples we find. The air is hot and still and the tufa coating on the rocks around us reflecs the sunlight, making the day feel hotter and brighter. We stalk snails in tiny inlets and pools, sifting through pebbles and combing through thick algae that will eventually decompose into tufa. We squat by the side of the lake for at least an hour but don’t see any signs of life, not even zooplankton. We can see flamingoes standing in the water at a distance, and other birds wheeling in the sky but what are they eating? Perhaps there are fish somewhere in this giant lake, but at its shoreline, all I can see is algae.
Later on, in the afternoon, we explore a stream cut that Jay had noticed, called Cerro Gorra. The stream had cut cleanly through former lake shores, leaving beautiful stratigraphic sections. We will spend time here in the next few days studying the layers and looking for shells.
