diverse population of microbes which have to tolerate extreme environmental conditions. Among these are the bacteria Amycolatopsis vastitatis, Lentzea chajnantorensis, Micromonospora acroterricola, Micromonospora arida, Micromonospora inaquosa, Modestobacter altitudinis, Modestobacter excelsi, Nocardiopsis deserti and Streptomyces aridus which were first isolated at the Purico complex. Some of these yield pharmacologically interesting compounds. Increased moisture availability during the ice ages caused the development of glaciers on Purico; at times, an ice cap with outlet glaciers covered an area of - at elevation on Purico. Apparently three different stages of glaciation occurred, the third between 30,000–25,000 years ago, the second between 50,000–60,000 years ago and the first over 100,000 years ago. Moraines associated with Lake Tauca appear to be either small or nonexistent. These glaciations have left moraines on Purico which extend for many kilometres at altitudes of , sometimes descending as far down as . The moraines reach heights of on the eastern side of Purico and on its western side. These moraines are covered with boulders and accompanied by striated surfaces and erratics. Penitentes still occur on Purico to this day. Eruptive history The Purico complex is the source of the major Purico ignimbrite, which was emplaced at the time of the Jaramillo geomagnetic reversal. It was originally called Cajon ignimbrite and attributed to an area northwest of Purico known as Chaxas. Also, the Toconao ignimbrite was originally attributed to the Purico complex, but now the La Pacana caldera is considered to be its source. The Purico ignimbrite itself covers a surface area of over the whole complex, and its volume has been estimated to be with an additional contributed by tephra fall deposits. The ignimbrite is thick and becomes thinner westward, with more distal sectors reaching thicknesses of . Potassium-argon dating has yielded ages between 1,380,000 ± 70,000 and 870,000 ± 520,000 years ago for the Purico ignimbrite. The large "dacitic dome D" has an age of 980,000 ± 50,000 and may thus have formed at the same time as the ignimbrites. The emplacement of the Purico ignimbrite was part of a pulse of activity in the Altiplano-Puna volcanic complex 1 million years ago. The Purico ignimbrite contains three flow units, the two Lower Purico Ignimbrites and the Upper Purico Ignimbrite. Their thicknesses differ; the Upper ignimbrite is thick while the two lower ones together reach an average thickness of , with a maximum of . The lowermost Lower Purico Ignimbrite