prekambriansk

Prekambriansk, commonly called the Precambrian in English, designates the broad span of Earth’s history from the formation of the planet about 4.6 billion years ago until the start of the Cambrian Period around 541 million years ago. It includes three eons: the Hadean, Archean, and Proterozoic. The term reflects the vast amount of time before complex, hard-shelled life became common in the fossil record.

During the Hadean, Earth’s surface was largely molten and gradually cooled to form a stable crust and oceans. The Archean saw the emergence of the first continental crust and the earliest known life, primarily single-celled prokaryotes, including cyanobacteria that carried out oxygenic photosynthesis. Rocks from this era preserve evidence of early geochemical and tectonic activity, though the processes operating at that time differed from modern plate tectonics in some respects.

The Proterozoic is marked by significant chemical and biological transitions. Oxygen began to accumulate in the atmosphere, especially after the Great Oxygenation Event around 2.4 to 2.0 billion years ago, though oxygen levels fluctuated thereafter. The era records growth of continental crust, the development of more complex life forms, and the appearance of early eukaryotes. By late Proterozoic times, multicellular organisms appeared, and the Earth experienced dramatic climatic episodes, including global glaciations known as snowball Earth events.

The Precambrian ends with the Cambrian explosion, when diverse life with hard parts proliferated in the fossil record. The Precambrian laid the planetary and biological foundations for later geological and evolutionary developments.