- The Eoarchean (IPA: /ˌiːoʊ.ɑːrˈkiːən/ EE-oh-ar-KEE-ən; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record. It spans 431 million years, from the end of the Hadean Eon 4031 Mya to the start of the Paleoarchean Era 3600 Mya. The beginnings of life on Earth have been dated to this era and evidence of archaea and cyanobacteria date to 3500 Mya, comparatively shortly after the Eoarchean. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar (around 10 to 100 times the atmospheric pressure today).
- Paleoarchean (Wikipedia)
The Paleoarchean (/ˌpeɪlioʊ.ɑːrˈkiːən, ˌpæl-/ PAY-lee-oh-ar-KEE-ən, PAL-), also spelled Palaeoarchaean (formerly known as the early Archean), is a geologic era within the Archean Eon. The name derives from Greek “Palaios” ancient. It spans the period of time 3,600 to 3,200 million years ago. The era is defined chronometrically and is not referenced to a specific level of a rock section on Earth. The earliest confirmed evidence of life comes from this era, and Vaalbara, one of Earth’s earliest supercontinents, may have formed during this era.
- Archean (Wikipedia)
The Archean Eon (IPA: /ɑːrˈkiːən/ ar-KEE-ən, also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth’s history, preceded by the Hadean Eon and followed by the Proterozoic. The Archean represents the time period from 4,031 to 2,500 Ma (millions of years ago). The Late Heavy Bombardment is hypothesized to overlap with the beginning of the Archean. The Huronian glaciation occurred at the end of the eon.
- Hadean (Wikipedia)
The Hadean (IPA: /heɪˈdiːən, ˈheɪdiən/ hay-DEE-ən, HAY-dee-ən) is the first and oldest of the four known geologic eons of Earth’s history. The Hadean eon started with the planet’s formation about 4.54 Bya, now defined as (4567.30 ± 0.16) Mya set by the age of the oldest solid material in the Solar System found in some meteorites about 4.567 billion years old. The proposed interplanetary collision that created the Moon occurred early in this eon, and the Late Heavy Bombardment is hypothesized to have occurred at the end of the eon. The Hadean ended 4.031 billion years ago, and was succeeded by the Archean eon.