to 485 MA)
with hard-shells appeared in great numbers during the Cambrian
explosion. The supercontinent of Gondwana had just formed and
near the South Pole. Gondwana, the supercontinent that was assembled
during the Pan-African orogeny, was the largest continent, spanning
from the equator to the South Pole. Because of a warmer climate
across the earth, much of the continental coasts as well as
were flooded below shallow seas, a perfect world as it were for
the dramatic radiation of new and complex forms of life during
Time (485 to 443 MA)
the Ordovician, oceans separated the continents of Laurentia,
Baltica, Siberia and Gondwana. Gondwana contained most land area,
and comprised Southern Europe, Africa, South America, Antarctica,
and Australia. Throughout the period, Gondwana drifted south.
North America lay on the equator and was mainly submerged until
the Middle Ordovician. Western and Central Europe were separated
and located in the southern tropics. Europe moved southward towards
the Middle Ordovician, uplifts occurred in most of the areas that had been shallow
shelf. Such uplists are known to be predictors of forthcoming glaciation. Increased
sea floor spreading and ridge activity accompanied by volcanic activity occurred.
Ocean currents changed as a result of lateral continental plate motions causing
the opening of the Atlantic Ocean. Sea levels underwent regression and transgression
globally, causing flooding of the Gondwana craton , inturn causing cessation of
in the Ordovician, a major glaciation began. This pervasive global event caused
a profound drop in sea level, draining nearly all craton platforms. The end of
the Ordovician was one of the coldest times in Earth history. Ice covered much
of the southern region of Gondwana.
Time (443 to 419 MA)
the Silurian, Laurentia collided with Baltica closing the northern
section of the Iapetus Ocean. This collision was preceded in many
places by the abduction of marginal island arcs, resulting in
the formation of the Caledonide mountains in Scandinavia, northern
Great Britain and Greenland, and the Northern Appalachian mountains
of Eastern North America. North China and South China had rifted
away from the Indo-Australian margin of Gondwana, drifting North
across the Paleo-Tethys Ocean. Throughout the Early and Middle
Paleozoic, the expansive Panthalassic Ocean covered much of the
northern hemisphere. Surrounding this ocean was a subduction zone,
much like the modern "ring-of-fire" that surrounds the
Time (419 to 359 MA)
Devonian realized profound changes in the world's geography. Landmasses
were concentrated in two supercontinents, Gondwana and Euramerica.
These vast continents close to other in the lower hemisphere,
while a vast ocean consumed the remainder of the Earth. These
supercontinents were surrounded on all sides by subduction zones.
With the development of the subduction zone between Gondwana and
Euramerica, a major collision was set in motion that would bring
the two together to form the single world-continent Pangea in
the Permian. The collision of what is now North America and Europe,
causes in huge granite intrusions and the uplifting of the Appalachian
Mountains. Erosion of new mountains provided great volumes of
sediment hat were deposited in the also and nearby lowlands and
shallow seas. Extensive
reef building, producing some of the world's largest reef complexes,
proceeded as stromatoporoids and corals appeared in increasing
numbers. These were built in the equatorial seas between the continents.
Large areas of shallow sea in North America, central Asia, and
Australia became basins in which great quantities of rock salt,
gypsum, and other minerals precipitated.
the end of the Devonian, a mass extinction event occurred. Glaciation
and the lowering of the global sea level may have triggered this
crisis, since the evidence suggests warm water marine species
were most affected. Meteorite impacts have also been blamed for
the mass extinction, or changes in atmospheric carbon dioxide.
It is even conceivable that it was the evolution and spread of
forests and the first plants with complex root systems that may
have altered the global climate. Whatever the cause, it was about
this time that the first vertebrates moved onto the land.
Time (359 to 299 MA)
Late Carboniferous Laurussia (comprising what is now Europe and
North America) collided with Godwanaland (comprising what is now
Africa and South America) producing the Appalachian Mountains
belt in Eastern North America and the Hercynian Mountains in the
United Kingdom. The collision of Siberia and Eastern Europe created
the Ural Mountains. Ice covered much of the southern hemisphere
and vast coal swamps formed along the equator in what is now North
marine environment existed in North America during the Lower Carboniferous
as seas submerged parts of the continents. In contrast, North
America during the Upper Carboniferous alternated between terrestrial
and marine domination as seas rose and fell in sequence with glaciation.
These environmental conditions coupled with the vast amount of
plant material produced in prodigious forests set the stage for
the production of vast amounts of coal over succeeding millions
of years. The burial of organically huge organic carbon led, in
turn, to a buildup of oxygen in the atmosphere to levels some
80% higher than today. Additionally, marine strata are more common
in the earlier Carboniferous than the later Carboniferous, and
nearly absent by the latest Carboniferous.