between about 570 and 480 million years ago suggests that this ancient sea-
coast faced a wide, deep ocean.
The Iapetus stretched at least 1,000 miles across from east to west and
bordered a much larger body of water to the south. It was dotted with vol-
canic islands and resembled the present-day Pacific Ocean between Southeast
Asia and Australia. The shallow waters of the nearshore environment of this
ancient sea from the Cambrian to the mid-Ordovician, about 460 million
years ago, contained abundant invertebrates, including trilobites, which
accounted for about 70 percent of all species. Eventually, the trilobites faded,
while mollusks and other invertebrates expanded throughout the seas.
The closing of this ancient ocean basin in the Ordovician as Baltica
approached Laurentia signaled the formation of Laurasia. Large-scale mountain
building followed the closing of the Iapetus when the continents flanking the sea
collided, pushing up mountains in northern Europe and North America, includ-
ing those that evolved into the Appalachians. The spate of mountain building
might have triggered a burst of species diversity.The largest of the increases was
the Ordovician radiation of marine species around 450 million years ago.Figure 69About 500
million years ago, the
continents surrounded an
ancient sea called the
Iapetus.
Historical Geology
NORTH
AMERICAEUROPEGONDWANAIapetus
Sea