7 November 2020 | New Scientist | 15AT THREE moments in the past,
Earth’s geological activity picked
up the pace. Its tectonic plates
moved faster than normal
and there were bursts of
volcanic activity and mountain
building that helped to create
supercontinents. These three
geological big bangs may have
played a role in the evolution
of life on Earth.
In 2014, Kent Condie at
the New Mexico Institute of
Mining and Technology and his
colleagues found that Earth’s
gigantic tectonic plates are
moving faster now than they
were a billion or so years ago.
That conclusion came from
analysing several types of data,
including magnetic signals
locked in ancient rock that
suggest where on Earth’s
surface the plates were at a
particular time in the past. This
can help establish how fast the
plates were moving at the time.
Now, Condie and his team
have analysed more data.
They say there is no longer a
signal suggesting the plates
have accelerated through time.
In its place is another, evenmore intriguing, pattern. At
three points in Earth’s distant
past – 600, 1100 and 1850
million years ago – the tectonic
plates sped up for a few tens of
millions of years, so that the
global average speed was 30 to
50 per cent faster than normal.
At the same time, there
were peaks in volcanic activity
and mountain building,
heralding the formation
of supercontinents – Nuna
at about 1850 million years,
Rodinia some 1100 million years
ago and the coalescence of landmasses some 600 million
years ago that would lead to
the formation of Pangaea.
“Something dramatic was
happening at those periods
of time that was affecting all
of these systems,” says Condie.
The researchers think this
is evidence of a vast geological
cycle that begins with the death
of a supercontinent. As it breaksup, some slabs of Earth’s crust
sink down into the mantle – the
thick layer of hot rock between
the crust and the core. Condie
says the slabs take 100 to 200
million years to drift down to
the bottom of the mantle. When
they arrive, the temperatures
and pressures turn the former
crust into a plume of hot rock,
which rises back to the surface.
“When that hot plume
hits the bottom of the
tectonic plates, it increases
plate speed, which in turn
increases orogenic [mountain
building] activity,” says
Condie, who presented the
work at an online meeting
of the Geological Society
of America last week.
“The notion that the deep
mantle is controlling the speed
of Earth’s tectonic plates just
before supercontinent assembly
is fascinating,” says Hugo
Olierook at Curtin University,
Australia. Earlier this year,
Olierook and his colleagues
presented evidence that,
110 million years ago during the
Cretaceous period, all of Earth’s
tectonic plates suddenly slowed
down by 25 to 50 per cent,
which they also linked to the
return of crust to the mantle.
Condie says it might be no
coincidence that two of the
three geological big bangs
roughly coincide with eventful
episodes in life’s history: the
appearance of complex cells
about 1.7 billion years ago and
the emergence of animals
about 600 million years ago.
“Plume events pump carbon
dioxide into the atmosphere,”
says Condie. “I think there
would be an effect on life.” ❚SOMEONE who types while on a
video call may be giving away more
than they realise. A computer model
can work out the words that the
person is typing just by tracking
the movement of their shoulders
and arms in the video stream.
“There are significant movements
that occur when typing,” says
Murtuza Jadliwala at the University
of Texas at San Antonio. “We
thought if we are able to model
them scientifically, we should be
able to infer different keystrokes
by looking at the video data.”
Jadliwala and his colleagues
developed a model to do just that.
They mapped the movements onto
a keyboard and cross-referenced
the results against a dictionary of
commonly typed words, finding
they could correctly identify the
word being typed 75 per cent of
the time. Their experiments were
conducted both in lab conditions
and using real-life video call data.
The computer model removes
the background information from a
frame of a video call. It then detects
the outer edges of the shoulder
by analysing each frame using an
image-processing technique called
optical flow, which traces how
pixels change in a video and maps
arm movements onto a keyboard.
Touch typers are more difficult
to discern than those who “peck”
at their keyboard, for whom the
model could recover 83 per cent
of words correctly. Those who
wore clothing with some sort of
sleeve were also less susceptible
to being analysed accurately
(arxiv.org/abs/2010.12078).
Jadliwala says pixellating
the shoulders would mitigate
the issue, but Alan Woodward at
the University of Surrey, UK, argues
such a solution defeats the purpose
of video calling. “The whole point
of a video call is to see people,” he
says, adding that it is alarming that
video calls can reveal so much. ❚The San Andreas fault is
where the Pacific and North
American tectonic plates meetTechnology GeologyChris Stokel-Walker Colin BarrasDAVIDPARKER
/SCIENCE^PH
OTO^ LIBRAR
YEarth may have had three
geological ‘big bangs’
Software can guess
what you are typing
during video calls
“ A hot plume hitting the
bottom of tectonic plates
increases plate speed
and mountain building”