Precambrian ENG

The time interval informally called Precambrian spans from the formation of the planet about 4.6 milliard years ago to the period 539 million years ago, encompassing around 6/7 of our planet’s history. It is divided into three eons: Hadean, Archean, and Proterozoic.

The Hadean period was about 600 million years long. The Earth was likely formed through gradual condensation of interstellar material. Later on, the first parts of the Earth’s crust appeared. The young planet was very hot and its surface was bombarded with numerous meteorites. Towards the end of Hadean, first atmosphere and hydrosphere emerged. No living organisms are known from this period. 

The Archean period spanned from 4 to 2,5 milliard years ago. The Earth had cooled down to the extent that enabled formation of the oldest documented sedimentary rocks. The cores of present-day continents called cratons were formed. The Earth’s crust was still too thin and kept transforming. The first atmosphere and bodies of water were demonstrably present towards the end of Archean. The climate was still very hot and humid. The most important phenomenon of this period is undoubtedly the emergence of living organisms on Earth. The oldest fossils (unicellular bacteria and cyanobacteria) are known from 3.5 billion years old deposits. 

During Proterozoic, which lasted for almost 2 milliard years, the planet underwent several orogenies. At the end of Proterozoic, tectonic plates merged into one supercontinent called Rhodinia. The first organisms with a cell nucleus – algae – emerged at that time. At the end of the period, there appeared first multicellular organisms called the Ediacaran fauna. Important evidence of life in the period are loaf-shaped biogenic structures called stromatolites that formed reefs.  

In our region, Precambrian deposits are found in Barrandien (near Prague). The mantle of the Krkonoše (Giant Mountains) and its piedmont yield gneiss and schists of this period.