Las ERAS GEOLÓGICAS y sus características / Escalas de tiempo geológico

Geological Time Scales and Their Significance

Overview of Geological Time Scales

• Geological time scales are vast periods used by scientists to categorize Earth's history, divided into five main categories: eons, eras, periods, epochs, and ages.

• Eons span billions of years; eras last hundreds of millions; periods cover around 100 million years. Smaller divisions include epochs and ages.

Importance of Major Events

• Geological eras are not fixed timeframes like decades or centuries but are defined by significant geological events that mark their beginnings and ends.

• For instance, the Archean eon concludes with the advent of photosynthesis, which dramatically increased atmospheric oxygen levels.

Breakdown of Eons

• There are three primary eons:

• Archean (4 billion to 2.5 billion years ago)

• Proterozoic (2.5 billion to 542 million years ago)

• Phanerozoic (542 million years ago to present).

Detailed Structure of Eras

• Each eon is subdivided into several shorter geological eras characterized by significant biological changes:

• The Mesozoic era includes three periods: Cretaceous, Jurassic, and Triassic.

Epochs and Ages within Periods

• Each period further divides into epochs; for example, the Jurassic period has three epochs: Late Jurassic, Middle Jurassic, and Early Jurassic.

• Ages represent the smallest units in this hierarchy; for instance, the Middle Jurassic epoch consists of two ages: Lalinense and Ian.

Characteristics of Geological Eras

Distribution of Eras in Geological Time Scale

• The geological time scale comprises ten distinct eras categorized under different eons:

• Archean (4 billion to ~3.6 billion years ago)

• Proterozoic (2.5 billion to ~542 million years ago)

• Phanerozoic includes Paleozoic, Mesozoic, and Cenozoic.

Key Features of Each Era

1. Paleoarchean:

• Duration: ~400 million years from ~4 billion to ~3.6 billion years ago.

• Notable for solidifying Earth's crust and forming the first continent.

2. Paleo-Proterozoic:

• Duration: ~900 million years from ~2.5 billion to ~1.6 billion years ago.

• Marked by a rise in atmospheric oxygen leading to anaerobic extinctions.

3. Meso-Proterozoic:

• Duration: ~500 million years from ~1.6 billion to ~1 billion years ago.

• Significant for sexual reproduction emergence among organisms.

4. Neo-Proterozoic:

• Duration: <500 million years from ~1 billion to ~542 million years ago.

• Characterized by major glaciations and evolution of multicellular life forms.

5. Paleozoic Era:

• Duration: From approximately 541 million to about 252 million years ago.

• Known for rapid diversification in marine species and formation/disintegration of Pangaea.

Evolutionary Milestones Across Eras

Mesozoic Era Highlights

• Known as the "Age of Dinosaurs," spanning from about 252 million to 66 million years ago with significant plant/animal evolution occurring during this time.

Cenozoic Era Developments

• Extending from approximately 66 million years ago until now; it began post-dinosaur extinction marked by mammalian development dominating terrestrial ecosystems.