Earth’s moon could have supported life billions of years ago

The
moon could have had conditions that supported life not once, but
twice.
REUTERS/Mike
Blake

• The moon could
  have supported life twice in its history, according to a new
  study.
• It’s possible that 4 billion and 3.5 billion years ago,
  the moon had liquid water, an atmosphere, and a magnetic field.
  It could have even had organic material.
• These conditions may have lasted for tens of millions
  of years — long enough for life to emerge.
• To search for any signs of past life on the moon, we’d
  need a close examination of the lunar surface.

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We may not need to travel far from our home planet to find a spot
in our solar system that could once have supported life.

Long ago, Earth’s moon may have had conditions in which life
could arise, according
to a study published Monday in the journal Astrobiology.

In fact, such conditions could have arisen on the moon during two
different periods, each tens of millions of years long, the study
suggests. The authors are not saying that life ever existed on
the moon — just that the conditions that make life as we know it
possible seem to have been in place billions of years ago.

When we look for signs of life on other planets and moons,
clues that can indicate a climate supportive to life include
liquid water, an atmosphere that would help keep water stable on
the surface, a magnetic field offering protection from solar and
cosmic radiation, and organic compounds that could make up life’s
building blocks.

According to the study’s authors, at least some of those key
conditions could have existed simultaneously on the moon. 

“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,” Dirk
Schulze-Makuch, a Washington State University astrobiologist and
co-author of the study, said
in a statement.

But astronauts and rovers have never found any evidence of life
on the moon, and even if organic material did once exist on our
planet’s satellite, we don’t know if any traces remain.

The moon likely formed
when a large planetary object collided with the
proto-Earth.
NASA image adapted by
Lock et al

How the moon could have supported life

The idea that the moon could once have been habitable is based on
a series of discoveries, mostly made within the past decade, that
show the moon isn’t as dry as we thought. There’s probably still
water ice in polar craters and
water deposits trapped in the moon’s interior.

Billions of years ago, there could have been good amounts of
liquid water on the surface, the new study says.

To understand why, a bit of lunar history is needed. Sometime
around when our solar system settled into its current layout —
about 4.5 billion years ago — a proto-Earth and another planetary
body likely collided and were vaporized,
according to a paper published earlier this year.

As this theory goes, the super-heated doughnut of molten,
vaporized rock and liquid — called a synestia — cooled, then the
moon emerged, after which the remaining cloud of vapor condensed
to form the Earth. For a long time after its formation, the moon
was largely molten, with an ocean of magma spewing gases into its
sky. 

Those gases could have been enough to create an atmosphere. As
that molten ocean finished solidifying (around 4 billion years
ago), there could also have been deep pools of liquid water on
the moon’s surface. That time period, the new study suggests, was
the first time conditions on the moon could have supported life.

The second time was during a period of intense volcanic activity
500 million years later — 3.5 billion years ago. That activity
could have created an even more dense atmosphere with more water
on the lunar surface, the study says. According to calculations
cited in the paper, there could have been liquid water on the
surface for 70 million years during that period, especially if
there was a magnetic field protecting the moon from solar winds.

Life could have first
emerged on Earth at hydrothermal vents.

OAR/National
Undersea Research Program (NURP); NOAA

Where early life could have come from

During both of these time windows,
life may have already existed on Earth. We still don’t know
how organic material first appeared on our home planet. It could
have been
delivered to Earth by tiny meteorites, or life could have
been the result of a
chemical transformation at volcanic vents in Earth’s oceans.
Scientists also still don’t know how common it is throughout the
universe for conditions that support life to exist. 

Some of the oldest evidence of life we have on Earth comes from
fossilized microbes known as cyanobacteria. Somehow, certain
precursor molecules — the chemical building blocks for life —
fused together to form organic materials, which evolved
eventually into those cyanobacteria. We don’t know exactly how
long that process took, but some researchers have estimated that
it was less than 10 million years.

By that logic, there could have been enough time for something
similar to happen on the moon. If organic material was there,
life could have emerged during these two windows.

Even if there was no organic material on the moon during those
years, they were periods of intense meteoric
activity. Schulze-Makuch and co-author Ian Crawford wrote in
the study that it’s “expected that meteorites blasted off the
surface of the Earth will have landed on the moon.” So those
meteorites could have brought microorganisms with them, which
might have survived the crash if slowed down by an atmosphere.

But many doubts still linger

Although the idea of life on the moon is intriguing, we don’t
know if the factors noted in the study ever came together to
enable life on the moon. Any efforts to find out more would
involve an “aggressive future program of lunar exploration,” the
study authors wrote.

Plus, even if there were relevant evidence on the moon, chances
are it’s been destroyed by billions of years of cosmic radiation,
solar winds, and meteorite strikes. Future missions to the moon
could, however, collect samples from layers of the moon that
might provide evidence about these periods of volcanic activity.
Lunar explorers could also eventually collect samples from the
craters that still might hold ice.

Further research could also involve simulation chambers that
would mimic the moon’s conditions to see if life could have
survived.

Regardless of any potential next steps, the researchers behind
the study think their work at least shows life could have existed
on the moon during these two periods.

“It looks very much like the moon was habitable at this time,”
Schulze-Makuch said. “There could have actually been microbes
thriving in water pools on the moon until the surface became dry
and dead.”