Geology Reference
In-Depth Information
arriveatsimilargeographiesofaworldwheretheAtlanticOceanhasovertakenthePacific
as the grandest body of water on Earth.
Fromthatpointon,modelsdiverge.Oneschoolofthought,calledextroversion,assumes
that the Atlantic will continue opening and the Americas will eventually crunch into Asia,
Australia, and Antarctica. In the latter stages of this supercontinent assembly, North Amer-
ica sweeps in from the east to close the Pacific and impact Japan, while South America
wraps around clockwise from the southeast to snuggle against equatorial Antarctica. It's
amazing how well all the pieces seem to fit together. Novopangaea is projected to be one
immense landmass stretching east to west along the Equator.
The central assumption of this extroversion vision is that the great mantle convection
cellsthatunderlieplatemotionswillcontinuemoreorlessastheydotoday.Thealternative
view, called introversion, takes the opposite tack by invoking past cycles of the opening
andclosingoftheAtlanticOcean.Reconstructions ofthepastbillionyearssuggestthatthe
Atlantic (or an equivalent ocean positioned between the Americas on the west and Europe
plusAfricaontheeast)hasopenedandclosedthreetimesonacycleofafewhundredmil-
lionyears—aresultthatsuggestsvariableandepisodicmantleconvection.Therockrecord
reveals that the movements of Laurentia and other continents about 600 million years ago
formed the Atlantic's predecessor, called the Iapetus Ocean (named for the Greek Titan Ia-
petus, father of Atlas). The Iapetus Ocean closed at the assembly of Pangaea. When that
supercontinent began to split apart 175 million years ago, the Atlantic Ocean was formed.
According to the introversion advocates (probably best not to call them introverts), the
still-widening Atlantic will follow the same pattern. It will slow, stop, and reverse in about
100 million years. Then some 200 million years later, the Americas will once again collide
with Europe and Africa. At the same time, Australia and Antarctica will have been sutured
to Southeast Asia to complete the future supercontinent of “Amasia.” This great landmass,
shaped something like a sideways
L
, uses the same puzzle pieces as Novopangaea but this
time with the Americas forming the western side.
Forthetime being,bothsupercontinent models, extroversion andintroversion, appear to
havemeritandarestillinplay.Andwhatevertheoutcomeofthisfriendlydebate,everyone
agrees that Earth's geography 250 million years from now, while strikingly different from
today, will echo past times. The transient collection of continents at the Equator will re-
ducetheimpactsoficeagesandmoderatechangesinsealevels.Mountainswillrisewhere
continents collide, while patterns of weather and vegetation shift and atmospheric levels of
carbon dioxide and oxygen fluctuate. Such changes will continue to be central to the story
of Earth.
Impact: The Next Fifty Million Years
