The Early Earth Wasn’t Completely Terrible

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. 

Artist concept of Earth during the Late Heavy Bombardment period. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab.

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.

This view of Earth from space is a fusion of science and art, drawing on data from multiple satellite missions and the talents of NASA scientists and graphic artists. This image originally appeared in the NASA Earth Observatory story Twin Blue Marbles. Image Credits: NASA images by Reto Stöckli, based on data from NASA and NOAA.

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. 

According to a new study, a comet impact triggered massive wildfires and a temporary cooling 12,800 years ago. Credit: NASA/Don Davis

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.

Source : Setting the stage: Building and maintaining a habitable world and the early conditions that could favour life’s beginnings on Earth and beyond

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