IDIOT’S GUIDES: SCIENCE MYSTERIES EXPLAINED
How can we be sure there wasn’t a technological
civilization living on Earth millions of years ago?
Are humans really the ﬁrst technology-using animal to walk the Earth? With a billion
years of history, it seems pretty unlikely! Though surely if smart city builders had lived
here before us, there’d be some kind of sign ….
The fossil record has nothing in it to indicate a technological species came before us. But we’ve made some
very particular changes to the world that should remain for millions of years—a sort of technological ﬁnger-
print for later life forms to discover …..
To be totally scientiﬁc about this, we have to say
that it’s still possible we are not the ﬁrst high-tech
species to live on Earth. And there is, hidden away
somewhere in the geological record, evidence of
super-smart dinosaurs or something similar.
After all, humans are just another kind of mam-
mal, and our species may even be less than a million
years old. Surely in the 135-million-year history of
the dinosaurs, there was at least one species that
used tools, made ﬁre, built houses … no?
To explain why there almost deﬁnitely hasn’t
been another high-tech animal on this planet,
it’s helpful to look at what humans would leave
behind if we all left or died out in the next few
For anyone visiting in the next hundred
thousand years or so, the evidence of human
habitation will be pretty plain. Our cities will
be buried under plants and our roads long since
eroded away, but alien scientists will, with a
little digging, be able to uncover all sorts of
junk—especially plastics, toxic wastes, and
certain metal objects.
After millions of years have passed, our for-
mer stewardship of Earth will be more dicult
to detect. But good scientists will still be able to
spot clues. Our quarries and mines, with their
unusual geometric fracturing of hard rock,
should endure for millions of years, though they
will be ﬁlled with sediment. Deep-penetrating
radar should be able to detect them, though.
There will also be unusual deposits of pure metals,
because we mined ore and reﬁned it into pure elemental
metal. The Earth will be strangely lacking in radioactive
isotopes of uranium on the surface—we used it in nuclear
reactors and weapons. And the distribution of such
rare-earth elements as lithium will be odd, too, because
we mined it and made it into batteries and other things.
Some of our metal tools, machines, and art could
survive for millions of years, especially bronze statues.
And if we do die out rather than leave, our legacy will be
preserved in the fossil record.
If fossils can show detail as ﬁne as individual feathers
and the points where muscle anchored onto bone, it’s
likely human civilization will leave all sorts of intriguing
shapes in rock strata.
Because of all this, it seems reasonable to assume
that if there had been a city-dwelling, jet-plane-ﬂying,
nuclear-reactor-building, high-tech civilization on Earth
before humans, evidence of this kind would remain. We
would see their mines, their machines, their culture
preserved in the rock, if nothing else. But as far as we can
tell, the Earth really was “primordial”—untouched by
technology—before humans evolved.
On the other hand, we should never underestimate
the erasing power of Earth’s tectonic and seismic activ-
ity. Much of the rock on the surface is new—geologically
speaking—and the signs of a prior civilization could have
been recycled back into the mantle by now. The fossil
record is, after all, enormously patchy.
For now, though, it looks like humans are indeed the
ﬁrst technological species to roam the Earth. Let’s hope
we’re not the last.