 Reporter Sarah Kaplan walking in a Welsh "cwm," an amphitheater-like geologic formation created when a glacier carves out a mountainside. (Courtesy Shoshana Akabas) | | | Most people go on vacation to get away from work. But science journalists (or at least, this science journalist) can't help being nerdy everywhere we go. This month I visited a friend in Wales, one of the most important countries to the early history of geology. Many of the 18th century British scientists who helped establish the field were inspired by Wales's fossil-rich cliffs and stark, stratified mountains. And a majority of geologic stages wound up being named after Welsh towns and tribes; the Cambrian — the period roughly 500 million years ago when complex life first emerged — comes from the Latin word for Wales, "Cambria." A lot of that foundational research was done in the mountains of Snowdonia, Wales's biggest national park. So of course, that's where I insisted we go hiking. The rocks in this region are as old as 625 million years, and have been shaped by events as recent as the last ice age. We clambered up to Cwm Idwal (pronounced "koom ID-wal"), an amphitheater-like valley scattered with huge boulders. Of course, I had to climb on top of the rocks.  Reporter Sarah Kaplan atop glacial erratics in Snowdonia, Wales. (Courtesy Shoshana Akabas) | | | It was only after we climbed down from the mountains that I learned I was not the first person to be captivated by these boulders. A century and a half ago, none other than Charles Darwin came to Cwm Idwal for a geology course. Close examination of these boulders revealed they held tiny fossils of sea creatures and marine plants — 1,200 feet above sea level. At one point, he realized, these rocks must have sat at the bottom of an ancient ocean. Though he didn't yet know how fossils wound up among the mountains (it would take another century for researchers to fully understand the process of plate tectonics), the discovery impressed upon Darwin Earth's deep history of profound change. Later that year, he set sail for South America on board the HMS Beagle — a voyage that would lead him to write "On the Origin of Species." Darwin was drawn back to Cwm Idwal in the 1840s, and was struck by something he overlooked on his first visit. The valley looked just like ones he'd seen in South America, with its steep curved walls and rocks bearing sharp parallel scratches. Even the huge fossil bearing-boulders were telling him something important. "A house burnt down by fire did not tell its story more plainly than did this valley," Darwin wrote. Glaciers were responsible for carving out this mountainside, he realized. Those gouges in the rocks were abrasions, those huge boulders were pieces of debris known as "erratics." These features were caused by the movement of a now-vanished river of ice. It was wonderful to feel so close to both geologic history and human history. To better understand not just what scientists know, but how they came to know it. If you're planning your own vacation, might I recommend traveling to look at rocks? | 
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