12 | New Scientist | 28 November 2020
TechnologyDavid HamblingA ROBOTIC cargo vessel has
passed through the Panama
Canal for the first time.
The ship, an Overlord uncrewed
surface vessel belonging to the
US Navy, made a 4700-nautical-
mile (8700 kilometre) journey,
including passage from the Atlantic
Ocean to the Pacific, almost entirely
without human assistance.
Pentagon spokesperson Josh Frey
says the vessel was in autonomous
mode for more than 97 per cent
of the trip’s length. A remote
crew assisted when needed.
The US Navy has two of the
59-metre Overlord vessels,
modified from crewed fast
transport ships. The modification
to uncrewed operations cost more
than $100 million for each vessel.
While the technology to guide
the large vessels may not be
novel, the willingness of the canal
authorities to allow the robotic ship
to pass through indicates growing
acceptance by the shipping industry.
“This is a significant achievement
that definitely shows it is possible
to undertake such passages and
operations,” says Jon Downes at
the University of Southampton, UK.
Smaller uncrewed vessels have
made extended journeys, including
a surfboard-sized Wave Glider,
which voyaged 14,700 kilometres
across the Pacific Ocean in 2013.
However, the Overlord trip including
the Panama transit was the longest
for a robot vessel of this size.
The Overlords are part of the
US Navy’s Ghost Fleet project, which
will supplement the crewed fleet
with many smaller uncrewed ships
for less demanding roles, such as
transport, clearing mines and
submarine-hunting patrols.
The civil sector is also developing
crewless vessels. Just as DARPA’s
Grand Challenge advanced the
technology for driverless cars in the
early 2000s, the US Navy may pave
the way for uncrewed ships. ❚Uncrewed US Navy
ship passes through
Panama CanalNews
GeologyMichael MarshallEARTH’S tectonic plates may
have begun moving 4 billion
years ago, almost a billion years
earlier than thought, according
to an analysis of ancient rocks.
The claim has earned a mixed
response from geologists.
Many argue that Earth was
too hot at the time for plate
tectonics in its modern form.
Today, Earth’s crust is divided
into several dozen rigid plates
that move slowly. Where two
plates meet, one can be forced
under the other and destroyed
inside the planet, a process
called subduction.
There is a growing consensus
that plate tectonics started
about 3.2 billion years ago. But
according to Brian Windley at
the University of Leicester in
the UK, that is wrong. “It really
is a great misunderstanding
of so many things,” he says.
Instead, Windley and his
colleagues argue that tectonics
began at least 4 billion years ago.
The evidence of a shift 3.2 billion
years ago, they say, merely
reflects a change in the way
the plates were behaving.
The researchers re-examined
data from rocks laid down
between 4 and 3.2 billion years
ago. They argue that many
of them contain evidence of
mountain-building, but of
a particular kind seen today
in a few places, including
Japan and the Caribbean.
When two tectonic plates
meet, if one gets subducted,
the volcanic activity this
generates can sometimes lead
to the formation of a chain
of volcanically active islands.
Crucially, the rocks of these
mountains are chemically
distinct from those that form
when continents collide – like
the Himalayas, which were
thrust up when India hit Asia.Windley and his colleagues
argue that before 3.2 billion
years ago, the only mountains
on Earth were formed by
subducting oceanic plates. Big
continents only started to form
about 3.2 billion years ago,
once the crust was thick enough.
This explains the shift in the
chemistry of rocks at that time,
says Windley (Precambrian
Research, doi.org/fjqr).
Not everyone is convinced
by the claim. “Plate tectonics
requires rigid plates,” says
Nicholas Gardiner at the
University of St Andrews, UK.However, billions of years
ago, Earth’s interior was hotter,
so the crust was probably less
rigid. If it was divided into
plates, he says, they wouldn’t
have behaved as they do today.
Instead most of the motion
may have been vertical, as less
dense rocks rose and denserrocks sank. Overall the system
would have looked different
to today, says Gardiner.
“There are really strongly
held views on either side of
this debate,” says Kathryn
Goodenough at the British
Geological Survey in
Edinburgh, UK.
Some researchers, like
Windley, have long argued for
an early start to plate tectonics,
while at the other end of the
spectrum, others argue that
modern plate tectonics began
only 700 million years ago.
Either way, it is becoming
clear that there was exposed
land as early as 3.5 billion years
ago, says Gardiner.
Sediments, which can only be
produced when rocks on land
are weathered, are known from
that time. The oldest confirmed
fossil organisms come from
the same rocks, and life may
have emerged in small bodies
of water on the first land. ❚Plate tectonics may have
got a very early start
NICK^1803 /GET
TY
IMAG
ESThe mountains of
Japan have a distinctive
rock chemistry“When two tectonic plates
meet, if one is subducted,
it can lead to formation
of volcanic islands”