Earth formed 4.54 billion years ago. The first period of the history of the Earth was known as the Hadean Period which lasted from 4.54 billion to 4 billion years ago. During that time, Earth was thought to be a magma filled, volcanic hellscape. It all sounds rather inhospitable at this stage but even then, liquid oceans of water are thought to have existed under an atmosphere of carbon dioxide and nitrogen. Recent research has shown that this environment may well have been rather more habitable than once thought.
The name ‘Hadean’ comes from Hades, the Greek god of the underworld. It nicely reflects the hot, hostile climate of the early Earth. During this period, Earth was largely a molten, chaotic world with volcanic eruptions a common sight on the landscape. Overhead, there would be regular visitors from space with meteorites and comets impacting the surface as the crust is still forming. Despite these conditions, it seems that water also began to accumulate as the planet cooled, possibly having been delivered by comets or released from outgassing from giant volcanoes. By the end of the era, the crust had solidified enough to form two early continents separated by forming oceans.
In a paper published by a team of researchers from the University of California they confirm this conclusion that, far from being in hospitable, early Earth was actually far less tumultuous. The team, led by Christopher K Jones explore the evolution of the Earth from formation to the evolution of life. They review a number of different pathways for the origins of life during the Hadean in the context of the large-scale planetary environment at the time, including Earth’s position in the Solar System.
In order to complete their work, the team look at the a number of critical aspects across different disciplines that included microbiology, atmospheric chemistry, geochemistry and planetary science. The relationships between life’s beginnings and the processes and state of the environment at the time is also assessed in their paper including the formation of the crust and evolution of the atmosphere.
The paper also explores a number of different atmospheric processes from wet-dry and freeze-thaw cycles to hydrothermal vent systems. This is not just assessed on Earth but in the Solar System at large to see if there is any correlation or overlaps. The impact of comets too are considered and how they would impact on the atmospheric chemistry.
The team conclude that Earth, during the Hadean period, most likely had liquid water. The debate still rages on however about the existence of continents and their composition. This uncertainty has an impact on just how organic life could have got a foothold on Earth. However it did, life would have taken a hold by the end of the Hadean era and started to leave evidence in the geological records of the Archean period that followed.
Unfortunately the paper is far from conclusive, leaving a number of questions unanswered but it does make a fabulous start to fill in the gaps at just how life began on this planet we call home.
“Artist concept of Earth during the Late Heavy Bombardment period.”
The paper points out that ” the severity and even existence of the late heavy bombardment is debated (Bottke and Norman, 2017).”
Else it has little to contribute on biology despite claiming it has a “focus on environmental requirements and
possibilities” such as biology informs us of. TimeTree has put the biological consensus dating of the oldest split between bacteria and archaea to 4.2 billion years for the last two decades of publications, and a recent paper puts the LUCA there by using a robust cross-bracing method.
“Here we infer that LUCA lived ~4.2?Ga (4.09–4.33?Ga) through divergence time analysis of pre-LUCA gene duplicates, calibrated using microbial fossils and isotope records under a new cross-bracing implementation. Phylogenetic reconciliation suggests that LUCA had a genome of at least 2.5?Mb (2.49–2.99?Mb), encoding around 2,600 proteins, comparable to modern prokaryotes. Our results suggest LUCA was a prokaryote-grade anaerobic acetogen that possessed an early immune system. Although LUCA is sometimes perceived as living in isolation, we infer LUCA to have been part of an established ecological system.”
Moody, E.R.R., Álvarez-Carretero, S., Mahendrarajah, T.A. et al. The nature of the last universal common ancestor and its impact on the early Earth system. Nat Ecol Evol 8, 1654–1666 (2024).