Hadean Eon
The Earth's origins, before the advent of life (probably)
The Hadean is the earliest eon in Earth's history; it occurs before the Archean Eon.
Geologic Age
4,567-4,031 million years ago
Subdivisions
There are no formal subdivisions in the Hadean
The Hadean Eon is divided (informally) into 4 periods
The International Commission on Stratigraphy, the governing body of scientists who determine the geologic timescale, does not officially recognize the Hadean due to the lack of actual strata from this period
What happened during this time?
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
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)
Additional Resources
Rain may have helped form the first cells, kick-starting life as we know it (The Conversation 15Oct2024)
└Agrawal et al. (2024) Did the exposure of coacervate droplets to rain make them the first stable protocells?
Did the first cells evolve in soda lakes? (Phys.org 20Mar2024)
└Cohen et al. (2024) Natural soda lakes provide compatible conditions for RNA and membrane function that could have enabled the origin of life
What was it like when life first sprang forth on Earth? (Big Think 8Jan2024)
The Very First Cells Could Have Bubbled Out of Hot Springs on The Ocean Floor (Phys.org 24Jan2024)
└Purvis et al. (2024) Generation of long-chain fatty acids by hydrogen-driven bicarbonate reduction in ancient alkaline hydrothermal vents
Ways for early life on Earth to survive cosmic radiation (Phys.org 6Dec2023)
└Dai et al. (2023) An inorganic mineral-based protocell with prebiotic radiation fitness