Sky and Telescope - July 2016 - 16

Cosmic Relief
David Grinspoon

The Golden Spike
of Tranquility Base
A modest proposal: the Anthropocene began with the lunar landings.
A far-future geologist studying Earth
history would observe that our time was one of sudden
and unprecedented planetary changes. Could this be a
type of transition that other planets also go through, when
cognitive systems begin to inﬂuence global systems?
I've written before about the proposal to formally
rename our current geological epoch the Anthropocene (S&T: Apr. 2013, p. 16) to acknowledge the fact that
humans have become a major force of global modiﬁcation. Within geological and other academic circles it's
been contentious but fruitful - sparking interesting
debates about how we humans should regard, and
attempt to guide, our own planet-altering presence.
There's no consensus over when exactly this humanized age began. Did it arise with the ﬁrst atomic bomb
explosions in the 1940s? If there was ever a time when
we started to realize we were all in the same boat, shooting holes in the hull, it was the dawn of the nuclear age.
We began to see what we'd become, and it left an indelible isotopic signature. This provides what geologists call
a "golden spike," a unique time stamp associated with an
event or transition. Others place the onset of the Anthropocene at the beginning of the Industrial Revolution, or

thousands of years earlier when we ﬁrst undertook largescale modiﬁcation of landscapes.
These arguments are most valuable if we read them
as a protracted dialogue on how humanity has journeyed
from being just another hominid species in East Africa
to the global force we are today. I view them as a series
of waypoints, each proposed origin marking a diﬀerent
stage in the "hominization" of the planet. Looked at in
this way, there is no single, correct moment of genesis.
But if geologists are going to formalize the deﬁnition,
they need to pin it to a speciﬁc stage in the rock record.
So let me oﬀer my own modest proposal for a "golden
spike" to mark the Anthropocene. If we must choose one
geological deposit that announces the human presence,
I would suggest the area of Mare Tranquillitatis where
Apollo astronauts ﬁrst stepped onto another world, leaving a ﬂag, machines, and footprints.
Those boot marks will fade in a few million years as
micrometeorites grind them into the dust, but signs of
our presence, including the alien artifacts we left, will be
detectable for as long as there is an Earth and a Moon.
These lunar landmarks could not have been made by a
species without world-changing technology. This altered
landscape also captures the moment we ﬁrst looked back
and saw the unity of our home and our common destiny
with all life on our planet.
Of course, as an actual proposal for correlating geological events on Earth, a Tranquility Base golden spike
is ridiculously impractical. But so what? There is nothing practical about the decision to formalize the Anthropocene Epoch. Any geologists, human or alien, studying
our time millions of years from now will not care about
our nomenclature. This is all about symbolism and our
self-image as we confront the challenges of this new age.
So, I know I'll lose but I vote for Tranquility Base. ✦
David Grinspoon is an astrobiologist, author, and senior
scientist at the Planetary Science Institute. Follow him on
Twitter at @DrFunkySpoon.

S&T: PATRICIA GILLIS-COPPOLA

July 2016 sky & telescope

Sky and Telescope - July 2016

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