Life Existed On Earth When Hades Ruled—It Even Had A ‘Rudimentary’ Immune System

The Earth formed from a molten mass of dust and gas orbiting the young Sun about 4.5 billion years ago. This period marked the beginning of the Hadean Epoch, named after Hades, the Greek god of the underworld, to reflect the hellish conditions of the time. The Hadean Epoch lasted from about 4.5 billion years ago to 4 billion years ago.

For decades, scientists have believed that life on Earth began 3.8 billion years ago, long after the time of Hades, a hypothesis supported by the oldest fossils dating back to this time. This timeline was thought to coincide with a “cooling period” on Earth, when conditions were right for life to take root and evolve. However, this long-held belief has been significantly challenged by recent research. Investigation resultpublished in the journal Natural Ecology and Evolution.

The last universal common ancestor dates back to the dawn of the Earth

Earth formed from the accumulation of dust and gas, emerging as a hot sphere with no stable landmasses or oceans. Initially, the surface was mainly covered by lava, and the planet was subjected to frequent and violent meteorite bombardments. This epoch, known as the Hadean epoch, featured a harsh landscape that seemed inhospitable to any form of life.

As the Earth’s surface gradually cooled, like a crème brûlée, the first solid crust began to form and water vapor accumulated in vast oceans, paving the way for the emergence of protocontinents.By the end of the Hadean and Archean epochs, roughly 4 billion years ago, Earth began to approximate its present-day shape, with land masses and large bodies of water emerging.

Recent findings suggest that the Last Universal Common Ancestor (LUCA) existed before this time, 4.2 billion years ago, when Earth’s topography was significantly different from today’s – when lava was still flowing and a solid crust was just beginning to form.

How do we know this if there are no fossils that survived the Hadean Era?

Tracing life back to the Hadean Era is a difficult task for scientists, mainly because traditional methods of archaeology and paleontology rely on a fossil record that simply doesn’t exist from this era: Earth was so intense and hot during the Hadean Era that any biological material from that time would have been destroyed or would never have been preserved in the first place.

However, by making full use of advanced genetic and molecular techniques, Physical fossilsScientists have been able to get around these limitations and date LUCA more precisely.

Why is accurate dating of LUCA important?

Dating LUCA to 4.2 billion years ago advances the timeline of life on Earth by 400 million years from the 3.8 billion years previously estimated based on the fossil record, and is significant for several reasons.

• The rapid emergence of life. The revised timeline highlights how quickly life emerged after Earth’s formation. Given that Earth is approximately 4.5 billion years old and was originally in a largely molten state, the emergence of life in 4.2 billion years suggests that life began shortly after Earth’s environment became minimally habitable. This rapid emergence suggests that the conditions necessary for life may be less stringent than previously thought and may be more common in the universe.
• The complexity of early life forms. According to the new findings, LUCA’s genome size was probably about 2.5 million base pairs, encoding about 2,600 proteins, similar to modern prokaryotes (simple single-celled organisms without a nucleus, such as bacteria). The findings also suggest that LUCA was a primitive anaerobe capable of generating energy through acetogenesis (a process that converts hydrogen and carbon dioxide into energy) and had an early immune system. The discovery that LUCA had a primitive immune system suggests that early life was not only able to colonize under harsh conditions, but also developed complex biological mechanisms at an early stage. This calls into question the previous idea that primitive life was overly simple, and highlights the inherent complexity of life from its very beginning.
• An ancient evolutionary arms race. The presence of an ancestral immune system in LUCA was likely a key adaptation for fighting off ancient viruses. This suggests that an evolutionary arms race between organisms and pathogens began almost simultaneously with the emergence of life itself, highlighting the constant struggle for survival and adaptation that has shaped the history of life on Earth.
• Geological and biological interactions. LUCA’s dating advances highlight the interplay between Earth’s geological development and the emergence of biology. The fact that life could thrive in such an unstable environment indicates a more dynamic interplay between Earth’s physical changes and life’s adaptability, reshaping our understanding of the influence of planetary processes on life.
• Implications for astrobiology. Knowing that life emerged quickly on Earth and developed complex mechanisms like an immune system within a very short geological time frame opens up the possibility of life on other planets, which could adjust the criteria for habitable conditions and what to look for in the search for extraterrestrial life.

In essence, this new dating from LUCA does more than add hundreds of millions of years to the age of life on Earth: it greatly advances our understanding of the resilience and complexity of life, changing the way we think about life on Earth and throughout the universe.