- 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.
- Mesoarchean (Wikipedia)
The Mesoarchean (/ˌmiːzoʊ.ɑːrˈkiːən, ˌmɛzoʊ-/ MEE-zoh-ar-KEE-ən, MEZ-oh-, also spelled Mesoarchaean) is a geologic era in the Archean Eon, spanning 3,200 to 2,800 million years ago, which contains the first evidence of modern-style plate subduction and expansion of microbial life. The era is defined chronometrically and is not referenced to a specific level in a rock section on Earth.
- Arsenic (Wikipedia)
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but only the grey form, which has a metallic appearance, is important to industry.
- 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.
- Eoarchean (Wikipedia)
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).