12 | New Scientist | 16 April 2022
News
AN EARTHQUAKE as large as any
in recorded history struck the
coast of Chile about 3800 years
ago, triggering a tsunami that
caused devastation along 1000
kilometres of coastline.
In the wake of the tsunami, local
hunter-gatherers began spending
less time near the coast and
moved cemeteries further inland,
staying there for 1000 years or
more, despite not having a system
of writing to convey information
about the disaster. It is a
remarkable example of a society
transforming itself to handle
natural threats, say the researchers
who studied the event.
The team, led by Gabriel Easton
at the University of Chile in
Santiago, spent years in the
Atacama desert on the west
coast of South America, gathering
evidence of an ancient tsunami.
At multiple sites, they found
a layer of distinctive sediment
dumped by a tsunami.
Radiocarbon dates from charcoal
and shells in archaeological
deposits directly overlying the
tsunami sediment suggest it
happened about 3800 years ago.It is impressive that the team
has found evidence over such
a wide area, says Eugenia Gayo,
director of Millennium Nucleus
Upwell in Concepción, Chile.
“It’s robust.”
The coast of Chile lies on a
subduction zone, where one of
the tectonic plates that make up
Earth’s surface is being forced
under another. As a result,
the region is prone to largeearthquakes. However, the written
record in this region is quite short,
so it is unclear how big the quakes
can be and how often the biggest
ones occur.
“We propose that this
earthquake was similar to the
Valdivia earthquake that occurred
in 1960 in southern Chile,” says
Easton. “This is the largest
earthquake ever recorded in
history.” The Valdivia quake had
a magnitude of about 9.5, and
Easton’s team says the tremor
3800 years ago was similar.
In theory, the Valdivia quakecould have been a one-off caused
by a very rare combination of
circumstances, says Easton. But if
a similar quake happened within
the past 5000 years, that can’t be
true. “This is our proposal, that
this area in northern Chile is
capable to produce earthquakes
of this size,” he says.
People have lived in the
Atacama for more than 12,
years. However, Easton and his
team documented major shifts
that occurred around 3800 years
ago. Archaeological sites near
the coast show less evidence of
habitation, suggesting people
stopped going there or at
least spent less time there.
Furthermore, cemeteries
were moved inland and uphill.
This new pattern of behaviour
lasted a long time, with many
coastal sites only being reoccupied
between 1500 and 1000 years ago
(Science Advances, doi.org/hpkh).
“This is kind of surprising,
because people usually have a
short memory for this kind of
event,” says Gayo. Maintaining
the behaviour for 1000 years
“is a lot”, she adds. ❚ArchaeologyMichael MarshallTIMW
HITBY
/ALAMYAncient Chilean tsunami scared local
people away from coast for 1000 years
The Atacama desert
has been occupied
for 12,000 yearsAstronomyTHE speediest stars in the galaxy,
moving at hundreds or even
thousands of kilometres per second,
are also some of the least well-
studied. A study of 15 of these
fast-moving objects has found
that most of them probably came
from dwarf galaxies devoured by
the Milky Way in the distant past.
“This is the first time that a
relatively large sample has been
analysed and evidence has beenshown that they are not from this
galaxy,” says Henrique Reggiani at
the Carnegie Institution for Science
in California. He and his colleagues
used telescopes at Apache Point
Observatory in New Mexico and Las
Campanas Observatory in Chile to
examine the light from 15 stars
with relatively high speeds and
learn their chemical compositions.
These stars aren’t the very fastest
in the galaxy, which are called
hypervelocity stars and move
with speeds in excess of 1000
kilometres per second, but rather
a category called extreme-velocity
stars, which move at hundreds ofkilometres per second and are
significantly easier to examine.
The researchers looked at the
relative abundances of 19 elements
in this set of stars. Stars from
different galaxies tend to have
unique combinations of these
elements based on their formation
histories, so this allowed the team
to distinguish what kind of galaxies
the stars were from.
Of the 15 extreme-velocity stars,the researchers found eight
with chemical compositions that
were definitively different from
Milky Way stars, suggesting they
formed elsewhere, while the rest
were inconclusive (arxiv.org/
abs/2203.16364).
The exotic stars were probably
born in smaller galaxies that were
swallowed up by our own. Over the
course of this messy galactic meal,
the gravity of the Milky Way would
have ripped apart the smaller
galaxies, swinging them around
and accelerating their stars to the
high speeds we see today. ❚Fast-moving stars
probably come from
other galaxies“The exotic stars were
probably born in smaller
galaxies that were
swallowed up by our own” Leah Crane