The Archean Eon
Lake Matano is a tectonic lake, formed by the shifting of the Earth's crust between one and four million years ago. It is the deepest lake in Indonesia, with a maximum depth of 590 meters (1,940 feet). The lake's surface sits 382 meters above sea level, meaning its deepest point is a cryptodepression—a basin that descends below sea level. This great depth and its tropical location prevent the water from turning over seasonally. As a result, the lake is permanently stratified into two distinct layers.
The top layer, or epilimnion, is a thin, oxygenated zone. Below this, the vast majority of the lake's volume is anoxic, meaning it contains no dissolved oxygen. This deep, dark water is also ferruginous, containing high concentrations of dissolved iron. This chemistry—anoxic and iron-rich—is believed to be a close match for the world's oceans during the Archean Eon, before the Great Oxidation Event about 2.5 billion years ago. The lake's water chemistry makes it a natural laboratory to study the biogeochemical cycles that may have governed early Earth. Scientists study microbes here, such as green sulfur bacteria, that perform photosynthesis using bacteriochlorophyll E in these low-light, no-oxygen conditions.