Our Milky Way galaxy contains tens of billions of potentially habitable planets, but we have no idea whether we’re
alone. For now Earth is the only world known to harbor life, and among
all the living things on our planet we assume Homo sapiens is the only species ever to have developed advanced technology.
But maybe that’s assuming too much.
In a mind-bending new paper entitled “The Silurian Hypothesis” — a reference to an ancient race of
brainy reptiles featured in the British science fiction show "Doctor
Who" — scientists at NASA’s Goddard Institute for Space Studies and the
University of Rochester take a critical look at the scientific evidence
that ours is the only advanced civilization ever to have existed on our
“Do we really know we were the first
technological species on Earth?” asks Adam Frank, a professor of physics
and astronomy at Rochester and a co-author of the paper. “We’ve had an
industrial society for only about 300 years, but there’s been complex
life on land for nearly 400 million years.”
went extinct today, Frank says, any future civilization that might arise
on Earth millions of years hence might find it hard to recognize traces
of human civilization. By the same token, if some earlier civilization
existed on Earth millions of years ago, we might have trouble finding
evidence of it.
discovery of physical artifacts would certainly be the most dramatic
evidence of a Silurian-style civilization on Earth, but Frank doubts
we’ll ever find anything of the sort.
“Our cities cover
less than one percent of the surface,” he says. Any comparable cities
from an earlier civilization would be easy for modern-day
paleontologists to miss. And no one should count on finding a Jurassic
iPhone; it wouldn't last millions of years, Gorilla Glass or no.
fossilized bones is a slightly better bet, but if another advanced
species walked the Earth millions of years ago — if they walked — it
would be easy to overlook their fossilized skeletons — if they had
skeletons. Modern humans have been around for just 100,000 years, a thin
sliver of time within the vast and spotty fossil record.
these reasons, Frank and Gavin Schmidt, a climatologist at Goddard and
the paper's co-author, focus on the possibility of finding chemical
relics of an ancient terrestrial civilization.
human technology as their guide, Schmidt and Frank suggest zeroing in on
plastics and other long-lived synthetic molecules as well as
radioactive fallout (in case factions of ancient lizard people waged
atomic warfare). In our case, technological development has been
accompanied by widespread extinctions and rapid environmental changes,
so those are red flags as well.
After reviewing several
suspiciously abrupt geologic events of the past 380 million years, the
researchers conclude that none of them clearly fit a technological
profile. Frank calls for more research, such as studying how modern
industrial chemicals persist in ocean sediments and then seeing if we
can find traces of similar chemicals in the geologic record.
argues that a deeper understanding of the human environmental footprint
will also have practical consequences, helping us recognize better ways
to achieve a long-term balance with the planet so we don't end up as
tomorrow's forgotten species.
Then again, he’s also a
curious guy who's interested in exploring more far-out ideas for finding
Silurian-style signatures: “You could try looking on the moon,” he
moon is a favored target of Penn State University astronomer Jason
Wright, one of a handful of other researchers now applying serious
scientific thinking to the possibility of pre-human technological
“Habitable planets like Earth are pretty
good at destroying unmaintained things on their surfaces,” Wright says.
So he’s been looking at the exotic possibility that such a civilization might have been a spacefaring one. If so,
artifacts of their technology, or technosignatures, might be found
elsewhere in the solar system.
SpaceX’s recent launch of a Tesla Roadster into space offers an insight into how such a search might go. Several
astronomers pointed their telescopes at the car and showed that, even if
you had no idea what you were looking at, you’d still quickly pick it
out as one weird-looking asteroid.
technosignatures in space is an extreme long shot, but Wright argues
that the effort is worthwhile. “There are lots of other reasons to find
peculiar structures on Mars and the moon, and to look for weird
asteroids,” he says. Such studies might reveal new details about the
history and evolution of the solar system, for instance, or about
resources that might be useful to future spacefarers.
If the efforts turn up a big black obelisk somewhere, so much the better.