About 700 million years ago, Laurentia collided with another large con-
tinent on its southern and eastern borders,creating a new supercontinent
called Rodinia.A superocean located approximately in the location of the pre-
sent-day Pacific Ocean surrounded the supercontinent.The collision thrust up
a 3,000-mile-long mountain belt in eastern North America called the
Grenville orogeny (Fig. 86). A similar mountain belt occupied parts of west-
ern Europe as well. Around 670 million years ago, thick ice sheets spread over
much of the landmass during perhaps the greatest period of glaciation Earth
has ever known.At this time, Rodinia might have passed over one of the poles
and collected a thick sheet of ice.
Rodinia rifted apart between about 630 and 560 million years ago, and
its constituent continental blocks drifted away from one another. As the con-
tinents dispersed and subsided,seawater flooded the interiors, creating large
continental shelves where vast arrays of organisms evolved. The rapid evolu-
tion of species at this time was highly remarkable. Another exceptional
episode of explosive evolution occurred when a supercontinent called Pan-
gaea rifted apart some 400 million years later.
The ancient North American continent was welded together from
scraps of crust called cratons about 2 billion years ago.The African and South
American continents did not aggregate until about 700 million years ago.Figure 86The Grenville
orogeny in North
America.
Historical Geology
Grenville orogenyGrenville orogeny