Last night I made dinner. I’ve never cooked over an open fire—only on a tiny gas-powered stove on backpacking trips–but Jay and Barbara have been teaching me how. Dinner was edible. Jay built the fire last night, but tonight I’m hoping to do the whole thing start to finish. Wish me luck.
We left Cerro Gorra this morning after spending all of yesterday taking dust samples and studying the Cerro’s stratigraphy. We were looking for ancient dust stuck in lake sediments. Dust floating in the air falls onto the lake and sinks to the bottom, where it gets trapped in mud. Normally, we’d have to drill a core into the bottom of the lake to get at these sediments, but drilling takes time and money. Lucky for us, the local climate and geology let us sample these sediments without drilling.
The lake’s water level has fallen over the last 20,000 years, leaving its ancient bottom sediments exposed. When a stream cuts through the layers of sediment, you can see the whole depositional record of the lake. We stood in the stream bed looking at its banks, and the layers of sediment deposited as the lake waxed and waned.
“Look,” says Jay, pointing to cobble layer between the sediments, “There’s an old shoreline with shells in it!” A few inches above the cobble layer was a layer of organic material. We hacked out chunks of sediment from those layers with our trowels and stuck them in Ziploc bags. Jay added shells from the layers to date their age. Once the shells are dated, we can estimate the age of the sediments.
Now we continue to the other side of the lake, stopping at Rio Bayo, on the north shore. We’re just about to move on to another area with better stratigraphy when we spot shells with brownish-green markings, different from the white shells we’ve been seeing for days. Finding pigmented shells comes as a surprise, though it shouldn’t since not all shells are bleached white once the organism inside dies.
Surprise number two: we find another kind of shell, fragile and scallop-like, the size of quinoa grains that break as soon as you touch them. Surprise number three: while collecting pigmented shells, we realize there are actually two different types. They look similar until you notice the wider aperture and tighter whorls of one species, plus other variations in shape. Once we see the difference, though, it’s hard not to hit yourself over the head and say “Stupid! Of course they’re different!”
This trip reminds me how easy it is to see what you want to see. Looking more closely at a shell or shoreline is how science advances, but learning to be this observant is incredibly difficult.
