JUNE 2019. DISCOVER 61
NEEDLES IN A HAYSTACK
The challenges of logistics and overcoming the field’s linger-
ing terrestrial bias pale in comparison to the power of nature.
Finding evidence of early human coastal dispersal is no day at
the beach.
“Half the battle in underwater work is understanding where
you should look within thousands of miles of landscape,” says
Amy Gusick, an archaeologist at the Natural History Museum
of Los Angeles County who has led underwater expeditions in
Mexico and the U.S.
“In underwater research, you have to understand sea level
rise, the cultural or historical context and also what kinds of sites
you’re looking for,” Gusick says. Shellfish foragers are likely to
leave different evidence at different kinds of sites, for example,
than mammoth hunters.
Plus, says Gusick, “you have to make sure you’re looking in
areas that have some chance of preservation.” Off the California
coast, for instance, “large portions [of continental shelf ] have
been annihilated by wave action and tidal force.”
Along the Canadian Pacific coast, the sheer weight of the ice
sheets pressed landmasses down during glacial maxima. As the
ice melted, the land sprang back up unevenly — a phenomenon
known as isostatic rebound. In some highly localized areas of
British Columbia, for example, Pleistocene sea levels are actually
several feet above the current shoreline. Add to that a host of
other forces that shape our world — such as seismic activity,
wind erosion and sediment buildup — and the complexity of
re-creating paleocoastlines becomes clear.
Now imagine you’re not only trying to locate these landscapes
— you’re also looking for signs of small bands of humans, travel-
ing with no more than what they could carry.
“The people would have been hunter-gatherers, foragers,
people in exploration and colonization mode,” says University
of Oregon archaeologist Jon Erlandson.ENGAGING YOUR CORE
To find evidence of a human presence, researchers begin not
by looking for evidence of people, but by reconstructing the
environment these early explorers would have encountered.
“We’re not on a treasure hunt,” says Todd Braje, an archaeolo-
gist at the California Academy of Sciences who is working with
Gusick, Erlandson and colleagues on a project in the Channel
Islands off Southern California. “We are mapping and sampling
paleolandscapes.... Once we’re able to predict landforms, the
soil, the ecology, we’ll start to have success identifying potential
archaeological sites.”
A paleocoastline research project often starts by developing
a customizable digital map from existing seafloor maps. The
new maps can highlight data specific to the project’s focus, such
as identifying sediment buried below the seafloor that could
indicate the course of a long-extinct river.
Researchers use these maps to zero in on areas of interest.
They then use different imaging tools to show both the sea-
floor and what’s beneath it on an ever-finer scale. Dependingon depth and conditions, the team might also deploy remote
sensing equipment or divers to refine their understanding of the
specific location.
Coring is often the next step, when researchers sample layers
of ancient soils, or paleosols, that were subsequently buried by
marine sediments as the sea levels rose.
Paleosols are typically full of pollen and microfossils of simple
organisms, such as diatoms, a
kind of algae that can indicate
climate conditions. The paleo-
sols may even preserve sedimen-
tary DNA shed from ancient
organisms. Identifying what
flora and fauna were present
at the site can help researchers
reconstruct the environment
and determine whether it might
have been attractive to human
hunter-gatherers on the move.SHELL GAME
An armchair archaeologist raised on myths of Atlantis and
Indiana Jones movies might be disappointed to learn that
researchers have more modest hopes for an Aquaterra find.
We’re talking shell middens.
These heaps of discarded shells exist the world over, some-
times the result of natural processes such as tidal deposition
or collection by birds — and sometimes the work of humans.
Bailey, who is researching massive ancient shell middens on
islands in the Red Sea, says the piles can record a surprising
amount of information about coastlines, climates and the pres-
ence of even small groups of humans.
“You don’t have to eat many oysters to have a big pile of shells,”
he says.
It’s also possible that individuals processing the shellfish,
removing the edible portions and tossing the shells, may
have left behind stone tools and other artifacts that confirm a
human presence.
Other materials that might be found at Aquaterra sites include
organic matter such as seeds, fibers and even wood. Fish and
other animal bones are also likely to survive, potentially preserv-
ing clues to the early humans’ diets.
As additional international projects get underway this
year to bring Aquaterra to the surface, researchers involved
in the work are united in their optimism about the field’s
growing momentum.
“This is really an exciting time,” Braje says of the new focus
on paleocoastlines in the human story. “Twenty or 30 years ago,
the questions we’re asking now would have been career suicide
because we had that [terrestrial bias] paradigm. Things have
fundamentally changed. It’s blown wide open.”
Erlandson agrees: “Over a 40-year career it’s been amazing to
see a 180-degree shift. Now there’s a broader understanding of
humans and our deep connection to the sea.”Fossilized diatoms, a kind of algae,
can be indicators of past climate.BIO
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