00:00Now, let's assume that another species, whether humanoid or dolphin-like, could have
00:05existed millions of years ago.
00:07How do we find their traces?
00:09There was a Doctor Who episode about a non-human industrial civilization on Earth that existed
00:14long before us.
00:16These reptiles, called Silurians, were forced deep underground by a catastrophic rise of
00:21temperatures on Earth, and there they thrived for centuries.
00:25That inspired scientists to create the so-called Silurian Hypothesis.
00:30If there was an advanced civilization before us, we should find their traces somewhere.
00:34Well, let's try.
00:37Climatologist Gavin Schmidt and astrophysicist Adam Frank decided to dive into this themselves.
00:44Like us, any technologically advanced civilization would be hungry for energy.
00:49So they looked for global effects that would leave a widespread mark.
00:53For example, hints of large-scale industrial processes, like plants and factories, and
00:59their leftovers.
01:01Then comes the question of how long these civilizations would last.
01:04If they existed for a long time, we should look for long-lasting signs, like residues
01:09from burning fossil fuels, mass extinctions, synthetic chemicals not found in nature, and
01:15even traces of nuclear fission.
01:17Basically, we should search for the same kinds of things that humans are currently leaving
01:22behind as evidence of our activities.
01:25Unfortunately, this evidence isn't that easy to find.
01:29Let's imagine an unsettling scenario if humanity suddenly disappeared.
01:34Even though it seems like we've left a lot of changes on our planet, the future civilization
01:39millions of years from now would struggle to find any remnants of our existence.
01:44Why?
01:45Well, our planet has existed for 4.5 billion years.
01:49Most life on Earth has existed for more than 400 million years.
01:53Compared to that, our industrial period only lasted around 300 years, and we haven't
01:59left any significant traces.
02:01Our record of Earth's history is full of gaps, especially the further back you look.
02:05The fossil record captures only some things, being very selective and incomplete.
02:11On average, one fossil emerges every 10,000 years, and dinosaur footprints are even rarer.
02:18Tides rise, oceans change, and plate tectonics can easily wipe out evidence of entire civilizations.
02:25After a couple of million years, chances are any physical signs of a civilization would
02:30disappear.
02:31In order to find at least something, we have to look for things like odd sediment patterns
02:36or unusual isotopic ratios.
02:39Also, fossils mostly form in water, leaving us in the dark about creatures on land or
02:45in the jungles.
02:47So even if there was a technologically advanced society millions of years in the past, and
02:52even if they were far more advanced than us, we might struggle to find any clues of its
02:58existence.
02:59Frank and Schmidt tried to understand how we could ever hope to spot signs of them.
03:04Discovering actual cities would be the ultimate proof of a Slurian-style civilization on Earth.
03:10But Adam Frank isn't too optimistic.
03:13Even now, our cities cover less than 3% of the surface, making it easy to miss ancient
03:18city ruins.
03:20Whether a city survives over tens of millions of years depends on whether the land around
03:25it is sinking, getting locked into a rock, or rising, getting worn away by rain and wind.
03:31So places like the French Quarter in New Orleans might have a better shot of making it into
03:36the geologic record than, say, Haight-Ashbury in San Francisco.
03:41When it comes to finding artifacts, the odds are pretty slim as well.
03:45No prehistoric iPhone would survive millions of years, fancy glass or not.
03:51Finding their fossilized remnants might be a bit more promising, but it's still tricky.
03:56Considering modern humans have only been around for about 100,000 years, it's quite possible
04:01that we might overlook any traces of an earlier advanced species.
04:08There is one thing, though.
04:09We could stumble upon their traces in rocks.
04:12Our current chaotic era might leave a distinct mark on the Earth's geological history.
04:18Especially since we're basically experiencing PTM 2.0.
04:21I'll get to that in a moment.
04:24So they try to look at the changes in the carbon cycle.
04:27Humans have been releasing a lot of fossil carbon since the 18th century.
04:31This leaves a special mark in the carbon isotope ratio, like a signature that shows the difference
04:37between carbon in living things, such as seashells, and carbon in lifeless volcanic rock.
04:44Scientists also look for signs in the way sediments are arranged.
04:47Large coastal deltas might mean that there were bigger rivers made by folks in this hypothetical
04:52civilization.
04:54Traces of nitrogen could suggest big-scale farming where they used a lot of fertilizer.
04:59Spikes in metal levels in the sediment could mean runoff from heavy industries.
05:04Of course, a single find like that wouldn't tell us anything.
05:08Schmidt says the key is to look for multiple signs together.
05:12Without clear artifacts, the uniqueness of an event might show in various clues rather
05:17than a set of changes linked to a single cause.
05:22On a quest for Silurian-style clues, scientists even decided to check the Moon.
05:28Some astronomers find it surprising that no one has looked into this before.
05:32They even joked about the possibility of dinosaurs building rockets and leaving traces
05:37on the Moon or other celestial bodies.
05:40These astronomers think that Earth-like planets tend to erase signs of civilizations on their
05:45surfaces.
05:46So, they're exploring the wild notion that these beings might've been space travelers.
05:51In that case, remnants of their technology, known as technosignatures, could be lurking
05:56not only on our Moon but also on asteroids, or even buried on Mars.
06:02Where they might endure for millions or even billions of years.
06:06Unfortunately, so far, despite digging into the past 380 million years and examining all
06:12suspicious events, the researchers haven't found a clear mat for a technological civilization.
06:19They don't give up, though.
06:20Frank calls for more investigation.
06:22For example, we could study how modern industrial chemicals stick around in ocean sediments.
06:28This, he believes, could help us identify similar chemical traces in the Earth's history.
06:34If there are no traces, why do we even bother to find something like that?
06:39This research is based on Schmidt and Frank's recent papers.
06:42They were delving into the Anthropocene.
06:44It's the proposed epoch dominated by human activities on Earth.
06:49It's full of these things called hyperthermals.
06:52They're prehistoric events when temperatures on Earth sharply increased over a relatively
06:57short time.
06:58They're like extreme heat waves from the past.
07:01A great example of this is the Paleocene-Eocene Thermomaximum, or PETM for short.
07:08It happened around 55.5 million years ago and saw a rapid rise in global temperatures.
07:14Over 200,000 years, the average temperature on Earth jumped from about 9 to 14 degrees
07:20Fahrenheit.
07:21We study these hyperthermals to understand how they occurred, from natural causes or
07:26human activities.
07:28So these hyperthermals sparked the genesis of Frank and Schmidt's research.
07:33To study them, scientists started examining chemical signals and tracers left in rocks.
07:40When doing that, Schmidt and Frank uncovered some eerie parallels between all the climate
07:45issues we have today and past periods of rapid temperature shifts.
07:49There's a close similarity between the PETM and other hyperthermal events.
07:54So all this work isn't just about solving a historical mystery.
07:59Understanding our impact on the environment can guide us to finding better ways to live
08:03in harmony with the planet and avoid becoming a forgotten species in the future.
08:09Our Milky Way is filled with lots of planets that could be just right for life.
08:14But we don't know if there are other civilizations out there.
08:17Earth is the only place we know of with living beings.
08:21About 200 years ago, people wondered if there might be civilizations on Mars.
08:26Back then, it was a real question.
08:28But once we got pictures from space probes, we decided there wasn't any evidence for
08:33it, and that idea got stuck in our minds.
08:36Now it's not even considered a valid topic for serious science.
08:40It's seen as kind of silly, but no one has set clear limits on what could've happened
08:45on our own planet a really long time ago.
08:48So even if there is no proof, we shouldn't throw away the possibility.
08:52Don't forget, it took humanity a while to recognize dinosaurs.
08:56Maybe Silurians are just patiently waiting for their time.
09:00That's it for today!
09:02So hey, if you pacified your curiosity, then give the video a like and share it with your
09:07friends!
09:08Or if you want more, just click on these videos and stay on the Bright Side!
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