When we think about alien civilizations we tend to look into the vastness of space,
to far away planets. But there is another
incredibly vast dimension that we might be giving too little thought to: time.
Could it be that over the last hundreds of millions of years,
other civilizations existed on earth? Indigenous technological species that
rose and died out? And that they or their artifacts are buried beneath
our feet? What does science have to say about this and what are the implications for us?
Life on earth has existed for 4 billion years, mostly as single celled organisms
until some 540 million years ago the Cambrian explosion heralded the age of animals. A huge
time window for our indigenous aliens. Where would we look for them and what could we hope to find?
Sadly we have only one civilization to look at: Ourselves.
Anatomically modern humans emerged around 300,000 years ago and probably lived in small
groups of hunter gatherers, slowly spreading around the world. Progress was slow and our
lifestyle did not change much, although there may have been local bursts of complexity.
Until about 10,000 years ago, when the agricultural revolution changed
our lifestyle forever, enabling massive population growth and technological progress.
Rather than just animals with culture and tools that would have been invisible from space,
we changed the face of the planet, cleared forests and
constructed cities and temples for our gods at breathtaking speeds and scales.
Until about 300 years ago, we became an industrial species and yet again
our numbers grew exponentially as did our impact on the planet.
We could say that our 300,000 year long history has three phases:
We were hunter gatherers for 97%, farmers for 2.9% and industrialists for 0.1% of our history.
And yet we are super new on earth.
On geological timescales, even the sturdiest things lose their durability. The oldest large
scale surface is in the Negev Desert, a meager 1.8 million years old. Everything older has been
crushed to dust or turned over and it is either below the ground, or covered by ice or ocean.
Our age, the Anthropocene will be a layer only a few centimeters thick in a few million years.
If there were aliens before us and they too went through these three phases,
what would remain of them? What can we learn about indegnous aliens by looking at ourselves?
Hunter & Gatherer Aliens
We actually know that in the last few million years, there were hunter gatherers aliens.
Our ancestors like Homo Erectus and cousins like the Neanderthals or Denisovans and probably many
more that we haven’t found yet or are lost to time forever. They left fragments of their bodies,
of weapons and tools and even art. Considering how long they existed and how little remains of them,
although they lived not that far from our present it is easy to think there have been others.
Intelligent animals like us that could talk and use tools and fire, that had culture and art. For
the last two million years, most hominins lived as hunter-gatherers – so if these aliens never moved
up higher on the tech tree, hundreds of different species and cultures could have existed without
leaving any traces. Their artifacts lost to biological and then geological processes.
At worst they would leave absolutely nothing to be found after thousands of years.
But what about fossils? We talked about how unlikely the process of fossilization is in more
detail in our dinosaur video, but in a nutshell, per hundred thousand years of earth's history
we only get a handful of good fossils. So we might easily just miss fossils of such people – but even
if we had any, we would not necessarily be able to identify them as hunter gatherers.
Agricultural and Empire Aliens
Looking at humans again, agricultural societies left much more to be dug up and found,
because they used more sophisticated tools made from sturdier materials and had to feed millions,
leaving many more artifacts. Farming allowed them to specialize and develop tech
from writing to navigation, architecture and government. Over thousands of years city
states became kingdoms and empires, some existing for millennia before they fell.
Many of the buildings or monuments they constructed are still around
and traces of them will exist for a few thousand more years. Some only as outlines in the ground,
but still recognizable to future archaeologists. The pyramids are piles of limestone so massive
that they will probably be around for hundreds of thousands of years. And because of the
greater numbers of humans that lived during our farm and empire period, we can expect way more
fossils and artifacts to be detectable, maybe for a few million years before they vanish.
So we can say with confidence that no such indigenous alien civilization existed in the
last few million years because otherwise we would have found something that they left.
This still leaves a window of hundreds of millions of years, back to the emergence of complex life,
where we would not be able to tell. If there were alien pre industrial societies and empires on the
level of the ancient Romans or Chinese, they would have likely disappeared without a trace. Their
tools, even advanced metals, would have rotted away. If they dug up canals, cleared forests and
built cities, their traces would be very hard to distinguish from nature. Maybe there once was an
empire of cephalopods occupying impressive cities in swamps and lakes, made from wood and stone.
Their engineers flooding land to build wet cities, their poets reciting poems in a language of
colors. Maybe they never industrialized – maybe their society was too stable or not inventive
enough or they never got a chance. A single event like an asteroid, an epidemic or an ice age
could just have deleted their civilization, ground up their temples as their soft bodies
rotted away. Sadly we don’t have the tiniest amount of evidence for any such civilization.
After a few million years at best, their achievements would have dissolved into nothing.
Industrial Indigenous Aliens
What about industrial civilizations, like humanity today? Imagine humans
died out suddenly, through a pandemic or cosmic rays or something like that. What would remain?
Our impact on the planet is orders of magnitude greater than that of our ancestors.
The fossil record will show a great extinction of wildlife
and an explosion of fossils from human associated animals, like rats, cows, pigs and chickens.
Like the structures of our ancestors, skyscrapers and streets and harddrives will basically crumble
into nothingness in a few millennia. But because there were so many humans everywhere,
for a few million years after our sudden end, there would be clear hints of our existence.
The byproducts of our industrial lifestyle might
actually give us away for some hundreds of millions of years .
We use massive amounts of artificial fertilizer which redirects earth’s flow of nitrogen that
is being deposited in the soil. Mining metals and rare Earth elements leaves long term scars
and depletes natural resources. We saturate our oceans with plastics that find their way
to the ocean floor and may persist for hundreds of millions of years.
There are radioactive elements and their decay, unnatural accumulations of elements that do not
exist outside labs or weapons. And of course, in our short industrial history we have changed the
proportion of CO2 in the air by burning massive amounts of fossil fuels, increasing the acidity
of the oceans and so on. We may already have left a mark in the geological record.
So far we have found no traces of an industrial alien civilization.
No layers of weird chemicals or displaced elements. No radioactive layer to indicate
that once great nations waged nuclear war. We do see mass extinctions and
massive shifts in the fossil records but no evidence that they did not occur naturally.
And ironically we’ve hit upon an interesting problem here: If industrial societies stress the
ecosystem enough to cause their own extinction, they won’t be around that long. But if they become
sustainable their imprint on the geological record may be tiny. If past industrial civilizations were
sustainable before they died out, we may have little to no chance of ever knowing about them.
In any case, over hundreds of millions of years these signatures may become
very subtle and get overlooked or interpreted as natural. Even if an industrialized alien society
existed 200 million years ago and lasted for 100,000 years, 300 times longer than
industrial humanity, it still might be easy to miss it in the geological record.
In any case, all of this is speculation. In the end we should not use our imagination to
trick ourselves into thinking we know anything about our blind spots. Just assuming a thing
happened because we don’t have evidence against it is a trap we should avoid.
So for now, if we look at the vastness of time it seems as
devoid of aliens as the vastness of space. Maybe we are alone in this universe and always were.
Maybe we’ll find traces of others eventually, we don’t know. But there is one important takeaway:
The continuation of our civilization is not guaranteed and if we are not careful,
we may disappear forever. Let’s hope that in a few million years,
there won't be another civilization studying our layer in the fossil record.
It’s frustrating to know there are so many things in our past we can’t access.
At least you can avoid that annoying feeling when it comes to other stuff you are interested in,
like your favorite TV shows or movies. You can make this possible by going to
NordVPN.com/kurzgesagt. NordVPNs service lets you change your virtual location by choosing from over
5200 fast servers in 60 countries all over the world and access regionally blocked content or
games that may not be available in your country. Secure your internet traffic with top-tier
NordVPN encryption, no matter if you’re using a Computer, Tablet or Smartphone.
It’s compatible with every major platform and can be used on 6 devices at once.
If you want to make the rest of your digital life airtight as well,
NordVPN also offers the secure Password manager NordPass and encrypted cloud storage NordLocker.
To explore all the games and shows you can get your hands on, go to NordVPN.com/kurzgesagt
for an exclusive deal for our viewers. It’s risk free with NordVPN’s 30 day money back guarantee.