Was LUCA the First Solar-System Astronaut, 4.2-Billion Years Ago?
A new Nature paper concluded that the Last Universal Common Ancestor (LUCA) of life on Earth had existed between 4.09–4.33 billion years ago, just a few hundred million years after the Moon-forming impact.
Earth formed 4.57 billion years ago. Following the collision that spawned the Moon when Earth was 60–175 million years old, Earth’s temperature reached about 2,300 degrees Kelvin (3,680°F), too hot for liquid water to support the chemistry of life as-we-know-it. It took tens of millions of years for Earth to cool significantly. The discovery of zircon crystals in Western Australia from 4.4 to 4 billion years ago, confirms the presence of liquid water during the inferred appearance time of LUCA.
The DNA of all living organisms today, from E. coli to humans, can be traced back to LUCA. The new study shows that LUCA was a complex organism, not very different from modern prokaryotes, and it possessed an early immune system to fight viruses. The early start of life on Earth suggests that it started quickly under similar conditions on other planets.
The radiative cooling of a planet scales with its surface area whereas its heat content scales with its volume. Mars is smaller than Earth and so it cooled faster because of its larger surface to volume ratio. There is definitive evidence that early Mars hosted an atmosphere and vast bodies of liquid water similarly to Earth. The early formation of life on Earth suggests that life could have started even earlier on a faster-cooling Mars. This implies that LUCA may have formed first on Mars and then transferred to Earth in the interior of rocks.
The feasibility of the transfer of life between Mars and Earth, labeled `panspermia’, is demonstrated by the Martian meteorite ALH84001 which was discovered in Antarctica in 1984. The interior of this meteorite was never heated above 40 degrees Celsius (104°F), implying that the rock was always below room temperature even before it was kicked out of Mars as a result of an asteroid or a comet impact about 15 million years ago. A higher temperature would have broken the magnetic coupling between lattice electrons and demagnetized the rock, in conflict with its detected magnetism. Given the low level of heating, Martian life could have survived in the interior of a similar rock that was ejected in a similar way during the first hundreds of millions of years in Mars’ history.
If LUCA was delivered to Earth from Mars, then we are all Martians. In that case, the first solar system astronaut may have been LUCA in Martian rocks, long before Yuri Gagarin ventured into space in 1961.
In case terrestrial life originated on Mars, the ambition of Elon Musk to establish a Martian base in a couple of decades is equivalent to the wish of returning to a childhood home. Musk told SpaceX employees in April 2024 that he expects one million people to be living on Mars in about 20 years.
Mars lost its magnetic field dynamo at most 3.9 billion years ago, and later lost its atmosphere and liquid water a few billion years ago. If intelligent beings existed on Mars just before it became the inhabitable desert we see today, future archaeologists might find prehistoric paintings on the walls of Martian caves and lava tubes.
If Mars had never lost its atmosphere, but instead gave rise to complex life as Earth did, then contemporaneous technological civilizations could have developed independently on both Mars and Earth. Imagine a virtual reality in which both Mars and Earth developed intelligent life at the same time, out of simultaneous seeding by the same LUCA, and the technological civilizations on both planets would have been engaged in an arms race as soon as they detected each other with their telescopes. Would such a reality promote peace among nations on Earth since all earthlings would feel a sense of urgency to cooperate?
The realization by earthlings that we are all in the same boat as a result of the existential threat from Martians might have shaped geopolitics to shy away from territorial disputes on the terrestrial rock. It would have been ridiculous for Russia to fight Ukraine while Martians are developing the equivalent of Musk’s Starship to reach Earth.
This sounds like science fiction, but it might become a reality if Musk’s wish gets fulfilled. Future generations of Martians will lose their loyalty to Earth and could engage in an arms race with earthlings. Once their territorial ambitions reach Earth, earthlings will have no choice but to cooperate. John Lennon never imagined this future in his song titled `Imagine’’, where he dreamed: “Imagine all the people Livin’ life in peace.”
Intelligent Martians could easily become the enemy of earthlings. As evident from our social media, the intelligent beings we hate the most are those that we know the least.
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For the related scientific paper, click here.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, was published in August 2023.
