When Armstrong and Aldrin returned from the Moon, they were decontaminated and locked in quarantine, lest they bring back infectious diseases. Soon enough, however, it was confirmed the Moon was utterly hostile to life. But according to a newly published theory, this was not always the case. The Moon has experienced two periods where it might have been possible for primitive life to survive there, either having evolved locally or been transported from the Earth.
Professor Dirk Schulze-Makuch of Washington State University noted the Moon is thought to have had major volcanic periods 4 billion and 3.5 billion years ago.
It is thought there was plenty of water vapor among the gasses released by these volcanoes, and Schulze-Makuch thinks this would have fallen as rain to create lakes and ponds. Today, with effectively no lunar atmosphere, water can’t stay liquid on the Moon's surface – it would turn to gas or ice almost instantly. However, the presence of all these volcanic gasses meant things were different then.
Writing in Astrobiology, Schulze-Makuch argues this would have created sufficient atmospheric pressure to keep these lakes liquid, perhaps for millions of years.
"If liquid water and a significant atmosphere were present on the early Moon for long periods of time, we think the lunar surface would have been at least transiently habitable," Schulze-Makuch said in a statement.
The Moon was then much closer to Earth, had a protective magnetosphere, and rotated quickly enough to avoid the blistering days and sweltering nights it has today.
Schulze-Makuch doesn’t rule out the possibility of life evolving on the Moon during this wet period, but the circumstances would have been less favorable than on Earth. However, we know the Earth was still experiencing numerous impacts at the time from large asteroids, which would have blasted rocks into space, sometimes carrying life.
“Some of the debris should have ended up on the Moon,” Schulze-Makuch told IFLScience. “A small but significant proportion.”
We know little about the lunar atmosphere at the time, but it was probably similar enough to Earth's atmosphere then as to not poison arrivals from Earth, raising the possibility they would have flourished there for a time.
Although any microbes that managed to live on the Moon during this period would be well and truly dead by now, Schulze-Makuch argues it is possible they could have left detectible residues behind. To test this, however, we are going to need to go back to the Moon, at least with robots, since none of the Apollo missions collected rocks from the relevant eras.
The theory will no doubt face much skepticism, but Schulze-Makuch is no crank, being an expert on life in dry places, including the Atacama Desert.
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