backstory Capsizing in canyons Susannah Porter, Carol Dehler and colleagues hiked miles in burning heat and braved unforgiving river rapids to sample rocks in the Grand Canyon.

■■ What was the objective of the work? ■■ any low points? We wanted to study life and the When our 22-foot motorized raft environment in the early part of capsized, we lost the entire kitchen to the Neoproterozoic era, 1,000 to the rapid, and the river guide lost his 542 million years ago, just before glasses. Our two field assistants swam the low-latitude (‘Snowball Earth’) the rapid — called Lava Falls — and glaciations around 726–635 million the river guides pulled them out at years ago. Relatively little is known the other end. Luckily, our samples about life and how it responded to remained dry. the major climatic and geochemical perturbations that took place during this ■■ What were the highlights of period. The Chuar Group — a lithified the expedition? sequence of Neoproterozoic sediments Working outdoors provided its own laid down in a shallow ocean in the rewards. After a day out in the field Grand Canyon area, long before the we would sit back and enjoy a gin Grand Canyon existed — contains and tonic around the campfire. And abundant and incredibly well-preserved as we fell asleep we could look up at fossil assemblages, and thus provided an the stars. A particular highlight of the excellent opportunity to examine this trip was when we rode through the interval in more detail. rapids and descended into ‘Powell’s bowels’ — where the oldest rocks in the ■■ Why did you choose this location? Grand Canyon frame the river passage. This is the only location where the These rocks formed deep in the Earth

Chuar Group is exposed, so there was no Dehler Carol approximately 1.8 billion years ago, and choice in the matter! are very different in appearance from the Susannah Porter and Shari Kelly sampling the overlying rocks. ■■ What sorts of samples were Chuar Group in the Grand Canyon. you after? ■■ Was it straightforward to get the We wanted fossils preserved in a detailed samples back to the lab? stratigraphic and sedimentologic geologists get bleached by the sun; rare On boat trips, we simply loaded the context, so that we could control for rainy days when it becomes impossible rocks onto the boats, and motored the palaeoenvironmental influences on fossil to take notes because of wet paper; ~150 miles downstream to camp (which patterns. Unfortunately, the majority of scorpions; mountain lion tracks; and took several days), to the boat ramp, the fossils are microscopic, and most of unnerving cliff passes. But perhaps most where we would get a shuttle back to the time we didn’t know whether we had scary was one of our trips to the field our cars. On the helicopter trip we collected any until we got back to the lab site where the Chuar Group rocks are had to restrict our sampling owing to and processed our samples. Nonetheless, exposed. Usually we would travel by boat weight limits, which was challenging. we knew from previous studies to (or once by helicopter), but one time a And on our epic 17–mile backpack target black, green and grey shale, and few of us decided to go by foot on an trip, we lugged the samples down to black chert. In addition, we discovered unmaintained ‘route’ along the North Rim the Colorado River (another five miles, incredibly abundant protozoan fossils in of the Grand Canyon. This is a 17-mile round trip), and stashed them on a beach carbonate nodules that formed in upper hike, and we miscalculated just how for a river guide to pick up later. Chuar Group shale. much water we would need. By the time we neared the end of the trail, we were ■■ Did the trip give you any ideas for ■■ Did you encounter all suffering from serious dehydration. future research projects? any difficulties? When we found a spring, we plopped We are now keen to look for evidence The are many down by the water, exhausted, only to find of the biotic transition in other rocks difficulties that there were poisonous plants growing of the same age, and to continue associated with in it. exploring the Chuar Group in working in search of more clues about the early remote parts ■■ Did you have encounters with Earth system. of the Grand dangerous animals? Canyon: really The greatest danger to us was the sun, This is the Backstory to the work by hot days when although we occasionally startled a Robin Nagy and colleagues, published on the rocks and the rattlesnake or a scorpion. page 415 of this issue.

E10 nature geoscience | VOL 2 | JUNE 2009 | www.nature.com/naturegeoscience

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