GONDWANA

  There once was a huge land mass around 500 million years ago.    It was called Pangaea. The pulling to and fro of the plates of the earth meant that this large mass broke into two pieces and Gondwana and Laurasi was formed.  

Gondwana extended from a point at or near the south pole to near the equator. Across much of Gondwana, the climate was mild.  the world was on average considerably warmer than today. Gondwana was then host to a huge variety of flora and fauna for many millions of years.

Gondwana began to break up in the early Jurassic era  about 184 million years ago accompanied by massive eruptions from volcanoes of basalt lava, as East Gondwana, comprising Antarctica, Madagascar, India and Australia, began to separate from Africa. South America began to drift slowly westward from Africa as the South Atlantic Ocean opened, beginning about 130 Mya   the   and resulting in open marine conditions by 110 Mya. East Gondwana then began to separate about 120 Mya when India began to move northward.

Australia began to separate from Antarctica perhaps 80 Mya  but sea-floor spreading between them became most active about 40 Mya.

New Zealand  is believed to have separated from Antarctica between 130 and 85 Mya.

As the age of mammals  commenced, the continent of  Australia-New Guinea began gradually to separate and move north (55 Mya), rotating about its axis to begin with, and thus retaining some connection with the remainder of Gondwana for about 10 million years.

About 45 Mya, the  Indian Plate  collided with Asia, buckling the crust and forming the  Himalayas. At about the same time, the southernmost part of Australia -  Tasmania  finally separated from Antarctica, letting ocean currents flow between the two continents for the first time. Antarctica became cooler and Australia became drier because ocean currents circling Antarctica were no longer directed around northern Australia into the subtropics.

The separation of South America from West Antartica some time perhaps 30 Mya, also caused  climate changes.  Immediately before this separation, South America and East Antarctica were not connected directly. However, the many microplates of the Antarctic Peninsula  remained near southern South America   and stopped oceanic current circulation. When the  Drake Passage   opened, there was no longer a barrier to force the cold waters of the Southern Ocean north to be exchanged with warmer tropical water. Instead, a cold circumpolar current developed and Antarctica became what it is today: a frigid continent that locks up much of the world's fresh water as ice. Sea temperatures dropped by almost 10°C, and the global climate became much colder.

By about 15 Mya, the collision between New Guinea (on the leading edge of the Australian Plate) and the southwestern part of the Pacific Plate pushed up the New Guinea highlands, causing a rain shadow effect which drastically changed weather patterns in Australia, drying it out.

Later, South America was connected to North America  cutting off a circulation of warm water 

A global reconstruction of the Earth during the Late Triassic, approximately 220 Million years ago, showing Gondwana breaking away from Laurasia in the north and the formation of the Iapetus Ocean.

 

BEFORE GONDWANA

Before  Pangaea forms, Gondwana was the core of  Pannotia. About 600 Ma. Pannotia was the landmass.  With so much landmass around the poles, evidence suggests that there were more glaciers during this time than at any other time in  geological history.

The laurel forest  of Australia,  New Caledonia  and New Zealand have a number of other related species  through the connection of the Antarctic flora  as gymnosperms and deciduous angiosperm Nothofagus. in Australia, New Caledonia and New Zealand. New Caledonia and New Zealand ecoregion are separated by  continental drift  from Australia 85 million years ago. The islands still retain  plants and  animals that originated in Gondwana and spread to the southern hemisphere continents later

 

.Early in the Ordovician, the continents Laurentia (present-day North America), Siberia, and Baltica (present-day northern Europe) were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move towards Laurentia later in the period, causing the Iapetus Ocean to shrink between them.

In the beginning of the Late Ordovician, from 460 to 450 Ma, volcanoes along the margin of the Iapetus Ocean spewed massive amounts of carbon dioxide into the atmosphere, turning the planet into a hothouse. By the end of the Late Ordovician these volcanic emissions had stopped.

Gondwana had by that time neared or approached the pole and was largely glaciated..  Sea level rose more or less continuously throughout the Early Ordovician, levelling off somewhat during the middle of the period.[10] Locally, some regressions occurred, but sea level rise continued in the beginning of the Late Ordovician. A change was soon on the cards, however, and sea levels fell steadily in accord with the cooling temperatures for the ~30 million years leading up to the Hirnantian glaciation. Within this icy stage, sea level seems to have risen and dropped somewhat, but despite much study the details remain unresolved.[10]

At the beginning of the period, around 480 million years ago, the climate was very hot due to high levels of CO2, which gave a strong greenhouse effect. The marine waters are assumed to have been around 45°C (113°F), which restricted the diversification of complex multi-cellular organisms. But over time, the climate become cooler, and around 460 million years ago, the ocean temperatures became comparable to those of present day equatorial waters.[11]

As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician. Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts.

Baltica (Northern Europe and Russia) and Laurentia (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay in waters which were at least temperate.

The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. The north–south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of Middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.

 

Sources: Wikipedia   http://en.wikipedia.org/wiki/