It's no secret that humans are the Earth's most dominant species.
And, without proof of life anywhere else in the universe,
we can probably consider ourselves the most dominant species in space too.
We know that complex life has existed on Earth for 400 million years.
But how could we look that far back?
Ancient ruins and artefacts only take us back a few thousand years,
geologic records only about 2 million,
So, if we can't rely on direct evidence,
then where else could we find traces of a potentially extinct civilization?
And what can we learn to make sure we avoid the same fate?
Here are some numbers to make your brain hurt for a second.
With all that in mind, it seems like there was ample opportunity
for another advanced civilization
to emerge, flourish, and die, all before we even showed up.
But finding any proof of a past civilized species seems like
it could be harder than even starting the civilization itself.
Physical artefacts would be the most concrete evidence
of past intelligent life, but it's not very likely that we will ever find any.
Over time, even our tallest buildings will crumble,
and our strongest materials will disintegrate.
Our cities cover less than one percent of the Earth's surface,
so any comparable cities
from past civilizations would be easy for paleontologists to miss.
Even if we knew where to look,
it's unlikely that these artefacts would last any longer than a few million years
Sure, there's always fossilization, but it only provides a limited record of the past.
Due to variables like when they lived and where,
an industrial civilization that lasted 100,000 years
-that's 333 times longer than we've made it so far-
might leave no fossil trace at all.
So maybe we're better off looking for more indirect evidence.
The best way to find that
would be to look at what traces our own civilization would leave behind
if it collapsed in its current state.
One place we're leaving a clear trail is in the sediment at the bottom of our bodies of water.
One look at this stuff, and you would immediately see the wacky chemical balances
that would imply some sort of outside influence.
For instance, the nitrogen fertilizers that we use to grow food
are running off into our bodies of water, and producing low oxygen
"dead zones" that would be visible in sedimentary layers.
On top of that,
we'll be leaving long-lasting synthetic molecules from radioactive fallout,
steroids, and all the plastic we dump in the ocean.
So yeah, future species are going to have a great impression of us.
In case we're not embarrassed enough, our technological advances
are rapidly changing the environment,
which has brought on widespread extinctions that would be visible in fossil records.
Ironically, perhaps the most promising marker of an advanced civilization
could be one of the very things that brought on its downfall.
When we burn fossil fuels, we are releasing carbon back into the air.
Fossil fuels ultimately derive from decayed plants and animals,
which contain a variety of carbon
that has a different atomic mass than most carbon in our atmosphere.
When this kind is released it changes the molecular make up of the atmosphere,
and leaves a clear signal to future scientists.
In a 2018 study, scientists hypothesized
that civilizations could even have fossil fuel driven life cycles.
When fossil fuel use leads to climate change, the oxygen levels decrease in the ocean
and help create a breeding ground for new fuels like oil and coal.
In this way, a civilization and its demise
might sow the seed for new civilizations in the future.
In our search for intelligent neighbors from the past,
we may never actually find any evidence,
but we can learn a lot about ourselves.
Analyzing our own long-term ecological footprint can have practical benefits.
It helps us recognize where we can do better, to achieve a balance with our planet
so that we don't become the forgotten civilization of tomorrow.
While it doesn't seem likely that intelligent life was here before us,
that doesn't mean there wasn't any.
For all we know, they were so advanced they were able to clean up their mess as they went.
The only verifiable way to check if someone was here before us
may be to rev up a time machine to go see for yourself.