Was Earth Terraformed by Martians?

Avi Loeb
4 min readDec 26, 2022

About 2–2.5 billion years ago, life in the Solar system witnessed nearly simultaneously good news and bad news. On the one hand, Mars lost its atmosphere and its surface reservoirs of liquid water, turning into the frozen desert it is today. But just around the same time, cyanobacteria abruptly raised the oxygen level in the atmosphere of Earth. This Great Oxidation Event enabled aerobic metabolism and the complex lifeforms that ultimately led to our existence.

Did this coincidence in timing between the two events occur by chance or was it triggered by cause and effect?

For example, if Mars lost its atmosphere as a result of a giant asteroid impact, the same collision could have transferred numerous Martian rocks with biological organisms or unique chemicals to Earth, tilting the balance in favor of cyanobacteria and triggering a transformation of terrestrial life. The possibility that Mars and Earth share the same biological ancestry will be testable as soon as we identify traces of life from Early Mars. But the ancestry could go deeper and involve intelligence.

In a previous essay, I calculated that if an advanced technological civilization originated on Mars twice as fast as on Earth and then disappeared when Mars lost its habitability, then all technological infrastructure on Mars would have been eroded into dust by now as a result of asteroid impacts. This natural devastation would have been equivalent to dropping several tens of Hiroshima atomic bombs per square kilometer on the Martian surface.

But let’s follow this logical possibility a bit further. If an advanced technological civilization existed on early Mars, surely there would have been a Martian version of Elon Musk who had founded a Martian company, say SpaceY, with the goal of bringing Martians to Earth after expressing a wish to die on Earth. And imagine that this wish was fulfilled 2–2.5 billion years ago, unlike the mirror-image of Musk’s current wish to die on Mars which is yet to be carried out.

In such a case, the revenues and stock value of SpaceY must have skyrocketed 2.5 billion years ago, when it became clear to the Martians that their planet is about to lose its atmosphere and ability to sustain liquid water. Inhabiting Earth became their obvious path to salvation, and terraforming Earth became a major priority in Martian politics.

Was the Great Oxidation Event the result of a Martian project for terraforming Earth? The rise in cyanobacteria activity could have been artificially cultivated by suppressing competing species, by seeding or by enhancing the nutrients that allowed cyanobacteria to thrive. In such a case, was the Great Oxidation Event on Earth followed by a Great Exodus Event on Mars?

Frankly, I do not enjoy science fiction when the storyline violates the laws of physics. But I do love science and this “Terraformed Earth” hypothesis is testable based on the scientific method. One could easily rule it out by studying early life on Earth or Mars and finding that the genetic code of living organisms on the two planets are different. But one could also search for archaeological evidence on Earth, Mars or even the Moon if an earlier civilization landed there.

Salt crater dating using data from the Mars Reconnaissance Orbiter implies that Mars had liquid water about 2–2.5 billion years ago. NASA’s MAVEN Orbiter presented evidence that Mars lost its atmosphere around that time. So far, the Perseverance Rover has not noticed any relics of Martian technology. But it is also possible to follow the latter search on Earth.

What would the archaeological traces of a Martian civilization on Earth look like? As calculated in my previous essay, the technological infrastructure of a civilization that predated us and then perished billions of years ago, would have been removed by meteor impacts and geological activity in the form of volcanoes and plate tectonics. But in places where the devastation was incomplete, we might find unusual relics.

Any such search would constitute a high-risk, high-reward operation. But the level of risk or reward associated with the search is far smaller than that involved in an actual exodus of a technological civilization from a rocky planet to its nearest neighbor. In case Martians arrived here first, Musk’s current ambition to bring humans to Mars resembles a trip plan to a childhood home after the parents passed away.

Incidentally, this is exactly what I did over the past few days while driving near the childhood farm where I was born, located in proximity to the Weizmann Institute where I am scheduled to deliver a public lecture on the Galileo Project — in search of extraterrestrial technological relics near Earth.

It occurred to me that in case we find anything, the answer to Enrico Fermi’s paradox: “Where is everybody?”, would be: “Right here, in front of us.”


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 chairs the advisory board for the Breakthrough Starshot project, and 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”, is scheduled for publication in August 2023.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".