Hadean Eon

The Hadean is not officially recognized by the International Commission on Stratigraphy, since no actual strata from this period now exist.

Marked by the formation of the solar system and the Earth

• Formation of the rocky Earth out of collisions of planetoids

• Formation of the Earth's crust

  • None of Earth's early surface survive from this time

Cosmic bombardments from comets and planetoids 

• In the cosmic stage, a still-forming Earth and our solar system took a daily pounding from rocky asteroids and icy comets between 4.1 to 3.8 billion years ago and brought the basic building blocks of life that could be concentrated and polymerized in the crater basins (Chatterjee & Yadav, 2022)

Earth's magnetic field was not present yet, thus not available to protect (proto-) life from cosmic radiation until 3.5 Ga

• Early protocells would have been able to survive due to protection by using polyphosphate manganese, to protect against oxidative stress (Dai et al. 2023)

• The living bacterium, Deinococcus radiodurans, uses a similar mechanism to protect against radiation.

Primal oceans with organic substrates

Reducing atmosphere: oxidation is prevented by the lack of oxygen and other oxidizing gases.

The origin of life (abiogenesis) might be possible during this time, but stronger evidence is needed.

• Evidence from a single zircon (out of 10,000) exhibited graphite inclusions (Bell et al., 2015)

• 12C-rich isotopic signature may be evidence for the origin of life on Earth by 4.1 Ga.

• Confirmatory evidence will be needed to show that this graphite was not contamination.

Zircons, or zirconium (IV) silicate (ZrSiO4), are common in the Earth's crust and found in all rock types (i.e., sedimentary, igneous, metamorphic)

They are fairly hard, stable, and resistant to heat and weathering 

They have played an important role in radiometric dating and represent some of the oldest minerals surviving on Earth

• Zircons from western Australia have yielded ages of 4.404 Ga (Wilde et al., 2001)