Geological Eras

The first era of Earth's time, starting with Earth's creation approximately 4.5 billion years ago.
Key events:
- Formation of the Sun.
- Creation of Earth.
- Creation of the atmosphere via volcanic out-gassing.
- Creation of the oceans.
- Creation of life.
Early life forms: simple, single-celled bacteria-like organisms.
Later in the era: development of more complex life, such as jellyfish and sea worms.
Few fossils exist from this era due to the soft-bodied nature of organisms.

Began with early invertebrates like trilobites and brachiopods.
Development of early vertebrate fish, then arachnids and insects.
Emergence of the first amphibians, with reptiles becoming dominant near the era's end.
Explosion of new plant life, starting with simple mosses and ferns.
Cone-bearing and seed plants became common by the end of the era.
A mass extinction event at the end of the era caused the disappearance of most marine invertebrates and amphibians.

Reptiles, including dinosaurs, were the dominant form of animal life.
Emergence of small mammals and birds.
Flowering plants appeared toward the end of the era, and mammal diversity increased.
The mass extinction at the end of the era led to the extinction of dinosaurs, paving the way for mammals to dominate.

The current era of Earth's history.
Began with a rapid expansion of new mammalian species.
Increased diversity of all life forms, with flowering plants becoming the most common.
The appearance of humans as the dominant species on the planet is a major event.