What is the Archaean eon?
Q: What is the Archaean eon?
A: The Archaean eon is the geological period after the Hadean and before the Proterozoic. It lasted from 4,000 million years ago (mya) to 2,500 mya.
Q: What type of rocks are found in the Archaean?
A: Most of the rocks which survive from this time period are volcanic (igneous) and metamorphic in origin.
Q: Was there plate tectonics during this time period?
A: The question of when plate tectonics began is a major research area, but it's possible that due to Earth's high heat flow during this time period, plate tectonics may have been more vigorous than today.
Q: Did oceans exist during this time period?
A: Yes, oceans existed before the start of the Archaean eon.
Q: What was present in Earth's atmosphere at this time?
A: The atmosphere almost entirely lacked free oxygen, and instead it was mostly methane and CO2.
Q: When did fossil life forms first appear on Earth?
A: Fossil life forms first appeared on Earth during the Archaean eon - these were cyanobacteria and acritarchs.
Q: When did oxygen begin to build up in Earth's atmosphere?
A: Oxygen began to build up in Earth's atmosphere much later - not until after 3,500 mya when fossil bacterial mats called stromatolites were formed by cyanobacteria using photosynthesis and giving off oxygen as a by-product.
