Recording-2025-02-23T14:37:47.931Z

Geological time refers to the history of the Earth from its formation to the present day.
The largest divisions in geological time are called eons.
There are four eons in Earth's history:
- Hadean Eon (oldest)
- Archaean Eon
- Proterozoic Eon
- Phanerozoic Eon (current)

The Hadean, Archaean, and Proterozoic eons are collectively referred to as Precambrian time.
Precambrian time occurred before the Cambrian explosion, which led to significant diversity in plant and animal life.
The diversity of life predominantly developed during the Phanerozoic Eon.

Timeframe: Approximately 4.6 billion to 4 billion years ago.
Named after the Greek god Hades, meaning underworld.
Conditions:
- Extremely hot with molten rock and high concentrations of carbon minerals.
- Atmosphere filled with toxic gases such as nitrogen and ammonia.
- Little to no breathable oxygen; most oxygen existed as water vapor, not in gaseous form.
No cells or life present.
Formation of Earth's core, atmosphere, and early rocks.

Timeframe: Approximately 4 billion to 2.5 billion years ago.
Name derived from Greek, meaning beginner or origin.
Significant events:
- Cooling of the Earth allowed the formation of oceans.
- Formation of continents; initial supercontinent formation.
- Emergence of protocells leading to prokaryotic cells.
Prokaryotic Cells:
- Lacked a nucleus and membrane-bound organelles, simpler than eukaryotic cells.
- Existence of stromatolites - layered structures formed by prokaryotic mats that fossilized.
- Introduction of cyanobacteria, capable of photosynthesis, increasing oxygen levels in the atmosphere.
Oxygen levels increased as cyanobacteria thrived, which resulted in a decline in anaerobic bacteria that could not survive in oxygen.

Timeframe: Approximately 2.5 billion to 541 million years ago.
Characterized by:
- Stable continents and established oceans.
- Increasing levels of oxygen due to the thriving cyanobacteria.
Emergence of eukaryotic organisms:
- Began as single-celled organisms (protists).
- Increased availability of oxygen allowed for the rise of multicellular eukaryotic life.
- Many multicellular organisms were aquatic, such as soft-bodied invertebrates (e.g., jellyfish).
Marks the end of Precambrian time leading into the Cambrian explosion.

Timeframe: Starts 541 million years ago and continues to the present.
Major developments:
- Notable increase in the diversity of life forms, particularly terrestrial organisms, plants, and animals.
The Cambrian explosion marks the onset of this eon, resulting in a rapid increase in the complexity and diversity of life.
Divisions of the Phanerozoic Eon:
- Paleozoic Era: Early diversification of plants and animals, transition from marine to terrestrial life.
- Mesozoic Era: Known for the rise of dinosaurs and further plant diversity.
- Cenozoic Era: Marks the rise of mammals and primates, leading to life forms contemporary to current times.