Earth Geological History: Precambrian, Archeozoic and Paleozoic Eras

Precambrian Era

The fusion of the Earth allowed its separation into two parts: a dense metallic core and a rocky mantle. This eon began approximately 4,500 million years ago and lasted until 2,800 million years ago.

Key Geological Events

• Differentiation: Formation of the metallic core and rocky mantle.
• Magnetic Field: Created by convection within the metallic core.
• Lunar Formation: Resulted from fragments ejected into space following a planetary collision.
• Atmospheric Development: Intense meteorite bombardment and mantle degassing created a dense atmosphere of water vapor and CO2.
• Hydrosphere: Initiation of the water cycle and the first granitic crust fragments, marking the beginning of plate tectonics.

Archeozoic Eon

Spanning from 3,800 to 2,500 million years ago, life emerged near mid-ocean ridges. Hydrothermal activity provided the necessary energy for bacterial life.

Biological and Environmental Changes

• Oxygenation: Bacteria colonized ocean surface layers, enriching the atmosphere and oceans with O2.
• Carbon Cycle: Decreased CO2 concentrations due to photosynthesis promoted limestone sedimentation.
• Greenhouse Effect: Reduced CO2 levels led to a decrease in the greenhouse effect.
• Atmospheric Nitrogen: Enrichment of N2 due to the action of decomposer bacteria.

Paleozoic Era

Covering the period from 541 to 252 million years ago, this era is defined by a massive diversification of life. It is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.

Geological Events

• Tectonic Shifts: Fragmentation of Rodinia led to the eventual formation of Pangea.
• Sedimentation: Warm, life-rich seas led to the deposition of limestone, sands, and clays.
• Orogeny: Continental collisions resulted in the Variscan (Hercynian) orogeny.
• Climate: Development of glaciations during the Ordovician and Carboniferous, followed by global desertification and intense Permian volcanism.

Paleozoic Materials and the Iberian Massif

Paleozoic materials form the foundation of the Iberian Massif:

• Cambrian-Ordovician-Silurian: Primarily shale and quartzite.
• Devonian-Carboniferous: Rich in limestone and coal seams.
• Orogenic Relief: Formation of the Cantabrian Mountains, Galicia, and the Sierra Morena, with significant granite deposits in Galicia and the central region.