The
area now known as Jamestown formed more than 565
million years ago, as part of a
microcontinent called Avalonia
(labeled the Avalonian volcanic arc in
this sketch of the southern hemisphere).
| The Avalonian arc formed as a
volcanic archipelago off of both Africa
and South America, at a time when they
were joined together as part of Gondwana,
part of which is shown in this sketch. At
that time, most of the world's
land masses were south of the equator. The
area that is now the Sahara Desert was
located over the south pole
!
Gondwana evolved after the breakup of Rodinia,
an earlier supercontinent. Other
major continents, then located in the
northern hemisphere, were Siberia and
North China.
Experts debate whether Laurentia was
in contact with South America at this
time. Those who believe they were, call
the larger continent Pannotia. In
any case, about 540 million years
ago both Laurentia
(proto North America) and Baltica
(proto Western Europe) drifted away from Gondwana.
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Rhode Island and
the New England states were not the only land
masses to emerge from the Avalonian arc. In
the sketch above, J
marks the approximate location of Jamestown. EW
indicates the portion of Avalonia that became
southern Ireland, England and Wales, Ib
shows Iberia (Spain and Portugal) and Ar
Armorica and Bohemia. A portion of the arc is now
part of Morocco. Future parts of Nova Scotia, New
Brunswick and Newfoundland, as well as most of
New England are offshore from Florida (labeled
F on the map). The portion of the arc
that became part of the Carolinas is to the right
of Jamestown, offshore of what is now Venezuela,
in South America.
Follow this link to find an
interesting account of unusual 565
million year old fossils found on Avalon
Penninsula in Newfoundland, and their
relataionship to fossils found in Charnwood
Forest in central England. These fossils
represent some of the earliest soft-bodied,
multi-cellular organisms.
About the same time that
Laurentia and Baltica moved away from Gondwana,
the oxygen content of air stabilized at close to
the current concentration.
Oceanic life forms began
to explode in complexity and diversity starting
around 545 million years ago. This
“Cambrian Explosion” resulted in a huge
variety of invertebrates including worms, clams,
arthropods, corals and sponges.
Laurentia
Moves Away from Gondwana
 |
| 500
mya: The Avalonian Arc grows while
Laurentia, Siberia and Baltica move away
from Gondwana |
Avalonia Moves Toward North
America
Starting about 500
million years ago, Avalonia drifted
north and west, away from Africa and toward Laurentia
(Proto North America). Most of Laurentia was
covered by shallow tropical seas in which were
found rapidly evolving species of trilobites and
echinoderms. Laurentia included not only the
central portion of the present United States, but
much of Canada, Mexico and Greenland. Movements
of the various land masses are depicted below.
The drawings are derived from Paleomap Project
views. (Plate tectonic maps and continental drift
animations by C. R. Scotese, PALEOMAP Project (www.scotese.com))
J
marks the approximate location of
Jamestown on these drawings. The full
world views, commentary and related links can be
accessed through the caption links.
As Avalonia journeyed across the
Iapetus Ocean, life around it was evolving.
Jawless fishes, coelenterates, arthropods,
cephalopods, jawed fishes and coral reefs
appeared.
About
435 million years ago, Avalonia docked with
Baltica. Both were moving north and
west, on collision courses with Laurentia.
Click this link to the next
installment of this narrative
Building
New England
The
Taconic and Acadian
Orogenies
About 450
million years ago an arc
of small islands collided
with Proto North America,
adding a strip of land
east of the Hudson River
Valley.
About 425 million years
ago, Avalonia collided
with Proto North America,
raising the Northern
Appalachians and adding
the remainder of New
England.
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