It stands out that the only inner rocky planet with a proper moon is earth.
Mars’ moons are tiny and very much unlike our moon, more like asteroids.
And Venus and Mercury lack a moon altogether.
This may indicate that forming moons may not have been easy for inner solar system planets,
and that’s if we can even call our moon a moon.
The Earth-moon system may be more accurately described as a double planet.
That might make our system rare, and also eyebrow raising in this regard is just how
our moon formed through a chance glancing blow with a Mars sized object early in earth’s
history.
While very likely not unique in the universe, that seems unlikely to happen very often in
the galaxy.
And it seems even less likely that it would happen at just the right time as to create
the conditions of this world as we know them today.
Because of this, our situation seems unusually special.
Even more so when you consider that it happened to a habitable planet that ended up with life
on it.
So this presents a question, what would Earth be like if it had no moon?
The answer is very different indeed, and it may have ended up to be so different that
life itself may have never appeared on this planet at all had things been otherwise.
Without the moon, it’s possible that earth might be lifeless today.
The most obvious difference would be the lesser tides.
Before we get into this, It’s worth noting that the tides are not solely an effect of
the moon.
In fact, about a third of the tidal effects that earth experiences are in fact from the
sun’s gravity, with the other two thirds being an effect of the moon’s gravity.
So the tides would not completely disappear, rather they would be muted and quite different.
But within the question of tides is a problem, they may have been a direct contributor to
the genesis of life on earth.
It’s thought that early in life’s history on earth, the chemistry that led to life occurred
in tidal pools.
It’s thought that once life arose, it was because of the tides that early life was able
to spread from one pool to another, ultimately allowing for it to colonize the rest of the
planet.
Think of it as a chemical colonization of tidal pools, and without the presence of the
moon and tides, this process may not have been able to happen.
The sun’s tides may or may not have been sufficient to do this on their own.
But there’s another effect on life here, the tides also help to agitate the ocean and
churn.
This is extremely important in the distribution of nutrients in the ocean, and without the
effect quite a bit of oceanic life on earth wouldn’t be able to survive.
We would have dead zones, and we do in fact.
The Black Sea’s circumstances are such that it has an anoxic dead zone below a certain
depth where very little can survive, which leads to wooden ships and even human bodies
-- it’s thought -- to last preserved for thousands of years because there’s literally
nothing down there to eat them.
It’s worth noting that the Black Sea represents a very special circumstantial case making
it unique on earth.
It’s thought to have been substantially altered very recently, well within human prehistory,
due to an influx of water from the mediterranean when the two bodies of water connected.
And the black sea does have tides of course, its dead zone is created by the dynamics of
the merger of two bodies of water.
But imagine if all of our oceans were like that, where the tides just weren’t large
enough to agitate nutrients?
Without nutrients, most of the bacteria couldn’t even survive, much less oxygen dependent fish
and just about everything that isn’t microscopic in our oceans.
But there would be more profound effects on earth if the moon wasn’t present.
One is that the earth used to rotate significantly faster than it does now, and it was the moon’s
gravity that slowed it down.
Without the moon, the earth today would rotate every eight to ten hours, as opposed to 24.
This would have made circadian rhythms in any biology early on very different, which
at the very least would have telescoped through to life on earth now.
Reproductive and sleep cycles would be different, and for a civilization like ours agriculture
and food production would be radically different, if not impossible.
And, what of the seasons?
For thousands of years we’ve been dependent on seasons for agriculture.
Even to this day, this is very carefully planned stuff.
We typically plant just after the last frost date for whatever zone we live in agriculturally
and then we expect to harvest at a certain amount of time thereafter, but before winter
for most crops.
Any gardener knows that this is the cycle of things.
But without a moon, this would all be very different.
And it wouldn’t just be the plants, life would have evolved very differently as well,
so could a civilization arise on a planet with very different, perhaps more extreme
seasons?
That’s an open question but the moon was key in defining it here.
Our agriculture could not be as it is without the moon.
But there’s more.
The moon also serves to regulate earth’s rotation, and without the moon to regulate
it earth’s axis would wobble far more than it does now.
This would make for a very different Earth, one where the polar caps would be extremely
unstable and rapidly grow and retreat on an almost constant basis.
Global temperatures would also vary wildly, and here is where the seasons would be completely
thrown off, with some periods having possibly having no discernable seasons at all, to much
more extreme changes to temperature in a period with seasons, depending on how earth happened
to be oriented.
This brings in questions of snowball earth, where it once in its history it seems to have
very nearly frozen over.
The microbial life survived, but in a more extreme situation they might not have.
It’s anyone’s guess if this might lead to a situation where microbial life arises
multiple independent times on an unstable world, only to get snuffed out each time as
the planet changes.
Another temperature related issue is that reflected light from the moon does actually
have a measurable effect on heating this planet.
It’s slight, nowhere near what direct sunlight does, though it’s still statistically significant,
and earth is somewhat sensitive to relatively small changes in global temperatures.
Without this effect, what might our atmospheric temperature look like?
And there’s always the question of the effects of the tides on ocean currents, which play
a role in weather patterns.
If the tidal effects of the moon weren’t present, then ocean currents and weather would
be immediately altered.
Another thing to note is that early in the earth’s history when life first appeared,
the moon was much closer to earth and would have had stronger tidal effects.
What effect that had one the early development of ocean life is not well understood, but
one hypothesis suggests that rapid changes in salinity in the coastal areas of earth
might have been crucial to the chemistry of life early on, which in itself would have
been affected by the larger tides at the time.
Had lower salinity been an issue, life might not have taken the same path at least, or
might not have gotten started at all.
And there are other concerns, without the moon the core of the earth would have spun
faster.
That would have made for a stronger magnetic field, and this also would also have made
for very different atmospheric conditions, but also a different situation for biology
if it was present, given that some species use the magnetic field for navigation.
An interesting question to ask might be what if the moon suddenly disappeared.
This is, of course, beyond highly unlikely.
But say it did, what would happen here on earth?
One thing is that balances that exist in the animal kingdom would immediately be altered.
Nocturnal predators often rely on dark conditions with varying levels of moonlight in which
to hunt.
With no moon at all, this becomes a serious problem.
Not so much for their prey however, animals such as rodents tend to take cover when the
moon is bright.
So you might see a decrease, or disappearance of nocturnal predators such as owls and an
explosion of rodents due to a lack of predators.
The loss of 2/3rds of the tides however would be devastating for coastal sea life.
Many species are dependant directly on the tides such as crabs and mussels, but indirectly
affected would be anything that fed on those animals, of which a great many land mammals
living near the coasts do.
Beyond the immediate effects, the instability issues would assert over time as earth no
longer has the stabilizing effects of the moon.
If some other immediate aspect of a calamity such as this didn’t end our civilization,
the increasingly unpredictable conditions of earth might at least force us to head into
space to colonize whatever we could.
We might abandon earth for Mars, or build giant habitats in space and forever forsake
our world of origin.
Biology itself would be very directly impacted if the moon went away, and might cease altogether
if earth froze over.
Gone would be the forests and macrofauna, leaving eventually a microbial world, much
like what earth was when life first began.
But even then, it may be relegated to an environment deep down in the earth, and no longer be a
surface phenomena.
Biology on this world lives in symbiosis with the moon.
It’s very possible that without the moon having been here since near the beginning,
life here on earth may never have come into being at all, and that includes us.
And, as an aside, if we had no moon, we would be totally without a dumping ground for tardigrades.
Recently Israel’s Beresheet spacecraft crash landed on the moon.
It was carrying several items of interesting, including at roughly 30,000 page digital archive
of various aspects of human civilization, along with human DNA, and thousands of dehydrated
tardigrades.
These samples were actually sealed in resin, and with tardigrades being among the most
resilient of earth’s complex life, if they survived the crash landing it’s anyone’s
guess how long the tardigrades can remain viable.
Perhaps decades from now someone will visit the site and see if the dormant lunar tardigrade
colony can be revived.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently plugging Event Horizon
again.
This week my guest is Isaac Arthur for a long form discussion of the Fermi Paradox, it’s
a great conversation and be sure to check out my books at your favorite online book
retailer and subscribe to my channels for regular, in-depth explorations into the interesting,
weird and unknown aspects of this amazing universe in which we live.