Geoscience Reference
In-Depth Information
Life on land was made possible in the first place by the adaptation of plants, the source of life-giving oxy-
gen. At first, plants kept their roots in the water and grew above the surface like reeds. Gradually they moved
away from the water's edge, and by the end of the Devonian, 10-meter-tall (30-foot) trees had evolved. These
were ancestral forms of the horsetails, club mosses, and ferns, which were to assume truly giant forms in the
Carboniferous (262-290 million years ago).
EUSTHENOPTERON
Horsetails are diminutive descendants of the giant club moss trees of the Carboniferous, or Coal Age.
THE CONTINENTAL PLATES
continued to coalesce, until a third megacontinent, called Gondwana— incorporat-
ing Australia, Antarctica, South America, Africa, India, southern Europe, and Florida—drifted into place and
melded with Laurentia. This formed a supercontinent that Wegener called Pangaea, or “one land,” which be-
came the starting point for his theory of continental drift. Pangaea would stay intact for the next 100 million
years.
As the continental plates closed and the mountains rose, a series of faults formed that produced deep basins
where parts of the Earth's crust subsided. Erosion of the nearby mountains, meanwhile, poured masses of sedi-
ments into these basins, which accumulated to thicknesses of several kilometers. The Maritimes Basin exten-
ded from central Nova Scotia northward across the Gulf of St. Lawrence to the shore of the present-day Gaspé
