JULY/AUGUST 2019. DISCOVER 43
Gondwana: Long-Lived
but Only Somewhat
Super
When: Formed at least 550 million
years ago; broke up around
180 million years ago.
What went where: Centered around
Antarctica, it included most of today’s
Southern Hemisphere landmasses.
What’s so super about it: While not
all geologists consider Gondwana
a true supercontinent, they do
agree it was around a lot longer
than Pangaea, which formed when
Gondwana joined Laurasia, another
semi-supercontinent. The longevity
of Gondwana, and its timing, gave
it a starring role in the evolution oflife on our planet. It formed around
the Cambrian Explosion, when
the fossil record suggests a rapid
increase in biodiversity. It then kept
itself together as plants and animals
emerged from the seas and onto
its shores. By the time Gondwana
began to bust up, dinosaurs and
other iconic animal groups had used
it as a superhighway to spread across
much of the Southern Hemisphere.
Pangaea: A Super-
Supercontinent
When: Formed as early as 335 million
years ago; began breaking up around
180 million years ago.
What went where: Most — but not all
— continental plates joined together
in a rough C shape, centered around
the equator.
What’s so super about it: Sometimes
spelled Pangea, this mighty mashup
was first proposed by German con-
tinental drift enthusiast Wegener in
the early 20th century. (He originally
called it Urkontinent, but an Anglicized
version of his other term for it, Pangäa,
was what stuck.) Although Wegener
was wrong about some of the details,
putting Pangaea on the map, so to
speak, was an important landmark
on the road to plate tectonic theory.
Researchers believe that when this
largest of supercontinents splintered
into smaller pieces, it completely
remade the global climate by forcing
massive shifts in ocean currents. A
2017 Nature Geoscience study found
the breakup released enough stored
carbon dioxide to cause additional
climate chaos.The Next Big Thing
When: About 100 million years
from now.
What’s going where: Likely in the
Northern Hemisphere, joining
the North American and Eurasian
plates — and possibly Australia
— around the North Pole.
What will be so super about it:
While models remain highly
theoretical, projections suggest
continental plates will bump
together next in the Northern
Hemisphere.
How to Date a Creep
A host of satellites, plus additional ground monitoring networks, precisely track current plate movement speeds.
To learn how fast these slabs of creeping crust moved in the past, researchers have a few tools.
Make a match: Rocks of the same age and composition — especially if fossils from the same ecosystem are present — likely
came from one formation. If pieces of that formation are found on different plates, researchers can measure the distance
between them and, using their age, calculate the speed of the split.
Follow the stripes: Earth’s polarity switches back and
forth over time. As magma cools into rock, magnetite
grains, dispersed within and aligned with the magnetic
field, become fixed: This records Earth’s polarity at the
time the rock formed. Oceanic crust, made of basaltic
rock and rich in magnetite, is created at divergent plate
boundaries, where the mantle is constantly coughing up
new magma. As the magma rises, cools and gets pushed
aside by newer magma, the magnetite within it preserves
a record of Earth’s fickle magnetic field. Seen on a sea-
floor map that shows this record, the periods of reversed
and normal polarity appear as stripes. This magnetic
striping can reveal how fast the plate boundary expanded
during a particular period of polarity, providing a broadersense of the speed of plate movement at that time.
?
Different models predict
different arrangements of our
continental plates in the future.
One potential up-and-coming
supercontinent is Amasia, above.E
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B AGE OF CRUST
DATING OCEANIC CRUST
Rising
magmaOceanic ridge
spreading centerEarth's
polarity1.060.900.78 present 0.780.901.06
millions of years ago millions of years agoNSNSNSNSSNSNSN