Cool science

1. Canberra Times (ACT : 1926 - 1995), Tuesday 14 November 1995, page 13
National Library of Australia http://nla.gov.au/nla.news-article130570301
Continents
make the
break
By GRAHAM BAKER
Scientists at Columbia
University's Lamont-Doherty
Earth Observatory have re-
ported that the Indo-Austra-
lian Plate, one of the 12 rigid plates
that comprise the Earth's crust, is
breaking in two.
Since cartographers began pro-
ducing reasonably accurate maps of
the world, geographers have
remarked at how the edges of some
continents seem to match others,
like pieces of a jig-saw puzzle. They
concluded that the Old and New
Worlds had, once, been joined but
had been torn apart by the Great
Flood. Apart from that cataclysmic
event, they believed that the posi-
tions of the continent were fixed.
However, evidence challenging
this view began to mount. The
study of fossils revealed that plant
and animal life had evolved in a re-
markably similar way in different
parts of the world.
Geologists found that mountain
ranges in widely separated coun-
tries contained rock strata of the
same type, deposited in exactly the
same order and of the same age.
Antarctica, Australia, Africa and
South America all exhibit grooves
worn by glaciers 270 million years
ago. Analysis of the grooves and of
the deposits left by the glaciers
indicates that those continents were
once joined together in colder
latitudes. Coral reefs, coal and salt
deposits can be found in polar
regions, proof that these lands once
experienced warmer climates.
In 1915 German meteorologist Al-
fred Wegener developed a theory
fred Wegener developed a theory
that accounted for this evidence.
His theory of continental drift pro-
posed that ail of the land surfaces
were originally combined in a sin-
gle large continent, which he called
"Pangaea". He theorised that
Pangaea broke up into continents
which gradually drifted to the
positions that they now occupy.
Wegener continued to develop his
theory until his death in 1930, but
failed to convince the scientific es-
tablishment.
The theory was resurrected in the
1950s by scientists studying magnet-
ism in the earth's crust. As molten
rock solidifies, the ferromagnetic
minerals in it align with the mag-
netic field of the Earth. Studies of
this magnetism showed that the
continents were in different
positions at various stages in their
history. One last piece of evidence
for continental drift was the discov-
ery of extensive mid-ocean moun-
tain ranges. Magnetometer surveys
either side of these ranges led
scientists to conclude that the crust-
al plates were moving away from
each other.
Current wisdom has it that the
mega-continent, Pangaea, started
breaking up around 200 million
years ago.
It split into two pieces,
Laurasia to the north and Gondwan-
aland to the south. Around 160 mil-
lion years ago, these super-
continents also started to break up.
Gondwanaland spawned the pres-
ent-day continents of Australia, Af-
rica, South America and Antarctica
and a subcontinent, India. Australia
finally broke away from Antarctica
about 80 million

2. Canberra Times (ACT : 1926 - 1995), Tuesday 14 November 1995, page 13 (2)
National Library of Australia http://nla.gov.au/nla.news-article130570301
about 80 million years ago.
Now, it
seems, that break up of
the earth's crust is continuing. The
Indo-Australian plate, after breaking
Stress on the central area of the Indo-Australian Plate is causing
it
to split.
away from Gondwanaland, slammed
into Eurasia 50 million years ago,
pushing up the Himalayan Moun-
tains. After about 40 million years,
as the Indian part of the plate
ground to a halt against its north
ern neighbour, the eastern end of
the plate bearing Australia started
to swing around in a counterclock
wise direction.
THE CENTRAL area of the
plate, at the equator under
the Indian Ocean, started to
buckle and split about eight million
years ago. This stress zone is more
than 1000km from east to west, and
was first discovered in the 1970s
when rock samples from the sea
bed were analysed.
Later research showed that the
seafloor was spreading out from
mid-ocean ridges to the west and
south of the stress zone. This could
only happen if the Indo-Australian
plate had split and, if this was the
case, then the eastern part of the
zone should be compressed, buckled
and cracked and the degree of
compression should systematically
increase from west to east.
In cruises aboard research vessels
in 1986 and 1991, scientists from the
in 1986 and 1991, scientists from the
Lamont-Doherty Earth Observatory
used sound waves to create images
of the sub-seafloor rock structure
along north-south transects of the
stress zone, 280km apart. The
images show scores of systematical-
ly aligned cracks in the ocean floor.
Slabs of the ocean floor are sliding
upward along the faults to alleviate
the strain, as the two halves of the
plate converge.
Careful measurements were made
along more than 200 faults to
determine just how far the blocks
of crust were thrust upward. The
observations showed that the thrust-
ing at the eastern transect is
about twice that at the western
transect; direct evidence that the
eastern plate is swinging around as
suspected.
"This is a newly observed way of
creating a new boundary between
plates," says Lamont-Doherty scient-
ist James Cochran. His colleague,
Jeffrey Weissel adds, "In the Cen-
tral Indian Ocean, nature is con-
ducting a large-scale laboratory ex-
periment for us, showing us what
happens to the oceanic lithosphere
when force is applied." When

3. Canberra Times (ACT : 1926 - 1995), Tuesday 14 November 1995, page 13 (3)
National Library of Australia http://nla.gov.au/nla.news-article130570301
when force is applied." When
pushed into an immovable object,
"it buckles like a piece of tin".
The new observations contribute
to our understanding of the Earth's
crust, its
response to stress and
how far it
can be stressed before it
breaks.
This insight will help scientists to
explain past geological events and
create better computer models. It
will also improve their ability to
predict earthquake and volcanic
activity.