November 5, 2006
Laguna Blanca refuge, Bolivia
Today the team visited a portion of a large stromatolite field that reaches to within a mile of the current shoreline of Laguna Blanca. It is one of the largest such fields known, covering an estimated 100 square kilometers (about 40 square miles). Stromatolites are layered structures built by cyanobacteria (photosynthetic bacteria). If it weren't for cyanobacteria, we wouldn't be here; they were responsible for putting oxygen into Earth's atmosphere.
Although stromatolites were once common in shallow waters worldwide - indeed, for some 3 billion years, they were the most prominent feature of Earth's biosphere - living stromatolites are rare today, existing in only a very few places. Sharks Bay, Australia, is the best known of these.
Most stromatolites found today are fossils, the remains of once-living colonies that have long since turned to stone. The stromatolite field near Laguna Blanca formed relatively recently. In 2002, members of the High Lakes team noticed them while exploring the terrain near the refuge. In 2004, they collected samples for laboratory analysis. Surprisingly, the stromatolites were found to be between 6,000 and 13,000 years old. This corresponds to a period in Earth history when a major climate change took place, marking the transition from the Pleistocene to the Holocene era. Around the world, glaciers began receding. In the altiplano, the transition marked the onset of drought and meant that lakes started to dry up.
Laguna Blanca and Laguna Verde were once part of a single, much larger lake, which covered the area where the stromatolites are found. Cyanobacteria lived and formed their impressive structures in the shallow waters of the lake, constantly finding new territory to colonize as the lake slowly dried away.
The High Lakes team in the stromatolite field near Laguna Blanca. Back row (from left): Macario, Rob, Nathalie, Eric, Clay, Sandy. Front row (from left): Henry, Edmond, Cristian, Matthieu./span>
Left: Matthieu breaks off a piece of a stromatolite with his rock hammer. Right: Most of the stromatolite field is heavily eroded, but in one section, a series of mounds about 3 to 4 feet in diameter are intact.
Left: Clay and Sandy chillin’ among the stromatolites. Right: Sunrise and moonset over Sairecabur, one of the volcanos bordering Laguna Blanca.
Left: Rob examines one of the long, sausage-shaped stromatolites. Right: This complex structure, about 30 feet long, is the remains of several stromatolites that merged together.