Gondwana - gone, but not forgotton

Modern Proteaceae

Modern Nothofagus

Fossil Nothofagus

Modern Araucariaceae

Fossil Araucariaceae

Plants Triassic Fossil

Animals Triassic Fossil

Radiation of first flowering plants(Angiosperms)

FRAGMENTS OF SOUTH EAST ASIA

For much of the time, Australia had an eastern and southern extension, with Tasmania and some associated thinner continental fragments to its west and south. While a large gulf opened west of Tasmania which allowed the Indian Ocean to enter, Tasmania prevented water flowing from the Indian Ocean to the Pacific Ocean. It also allowed migration of plants and animals from South America, through Antarctica and Tasmania to mainland Australia.

Since about 33 million years ago, Indian Ocean water could flow south of Tasmania to the Pacific Ocean and circulation began around Antarctica for the first time. This water became progressively colder until snow and ice began to accumulate on Antarctica which previously had been fully vegetated with plant groups that, in an evolved form, still exist in Tasmania, New Zealand, southern South America and adjacent islands. The Antarctic ice-sheet evolved, and wiped out any vegetation other than mosses and lichens. At the same time, migration of animals and plants between Southern Hemisphere continents through Antarctica ceased, and Antarctica, Australia and South America became isolated continents. Plants and animals on these continents began to evolve in different directions.

Continental drift means that continents continually move, sometimes collide, drift apart and periodically rejoin to form supercontinents. 600 million years ago, there was one supercontinent, know as Pangaea. Gondwana and Laurasia came into being about 500 million years ago when Pangaea slowly split into two. Laurasia consisted predominantly of North America and Eurasia. Gondwana included mainly Australia, Antarctica, South America, Africa and India.

About 160 million years ago, the separate components of Gondwana began to drift apart. First to go was a fragment off north-western Australia, and at the same time, a rift developed between India and Africa.

At 130 million years, Africa/South America began to move north and separate, forming the South Atlantic Ocean. India commenced its northward path, allowing the Indian Ocean to enter along much of the Antarctic coast. This left Antarctica and Australia joined along Australia’s southern margin.

Eventually, in the last stage of Gondwana’s disintegration, Australia separated from Antarctica. This began about 90 million years ago and initially was so slow that it had no real effect, until 50 million years when the movement accelerated to the current 6cm per year.

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Showing the decline and extinction of most life forms on Antarctica followed by a postulated reduction in specialised oceanic life in the surrounding seas as a reaction to the changes in food availability.

Gondwana, Tasmania and the modern world

Showing the decline and extinction of most life forms on Antarctica followed by a postulated reduction in specialized oceanic life in the surrounding seas as a reaction to the changes in food availability.

Gondwana, Tasmania & the Modern World

Energy in the Forest - Water

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FIRST ANIMALSMARINE INVERTERBRATES

FIRST ANIMALSMARINE INVERTERBRATES

Glaciations

Extinction Event

Extinction Event

9. Unforested slopes shed rainwater quickly, eroding their surfaces thus making streams muddy or silty and contributing to flooding.10. Understorey layer of ferms, shrubs and other plants. 11. Water absorbed into forest litter. 12. Low level groundwater taken up by tree roots. 13. Water from the litter layer passes into the soil as groundwater; the surplus goes into the river. 14. The water flowing out of the forest is clear. 15. Muddy water from the bare hillsides.

1. Rain. 2. Water of transpiration. 3. Upper or first canopy. 4. Rainwater absorbed onto leaf and stem surfaces trickles down the branches and trunk to reach the litter layer, from which enters the soil to become surface and ground water. 5. Second canopy. 6. This tree illustrates the circulation of water in all forest trees. 7. Third canopy. 8. The forest acts as a sponge, slowly releasing rainwater into streams, which remain clear.

TREES AND FORESTS, ENERGY INTERCEPTORS AND CARBON CONVERTERS

Forests have accumulated huge amounts of carbon in the forms of living trees, leaf litter and in the soil. From the atmosphere’s 640 billion tonnes some 16.5 billion tonnes is taken up by land plants each year, more is taken up by phytoplankton and other aquatic plants.

This carbon has been fixed by some 5% of the solar radiation that reaches the earth’s surface driving the process of photosynthesis that turns ground water containing dissolved minerals and carbon dioxide into a place of colossal biological activity supporting complex ecosystems built on the food provide by plants.

During this process trees transpire huge quantities of water each day and can have an effect on local climates such as causing cloud forests on mountains.

Trees also intercept rainfall and absorb its energy, slowing its descent to the ground so protecting the soil from erosion. Also by storing water on the leaves and trunks and in the litter layer forests work to regulate the flow of water by extending the time it takes for it to runoff.

Forests reduce the destructive effects of soil erosion to manageable proportions, they do not eliminate them.

The distribution of modern plant families and genera, combined with the fossils, provide evidence for the former combinations of the continental plates. New Zealand also has modern Nothofagus.

Plants evidence - ancient continent

Origin & Evolution of Gondwana

Australia

Antarctica

India

Africa

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New

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Madagascar

120 Ma120 Ma

Antarctica becomes ice covered some 30 million years ago (mya) ending a long period of a wide diversity of life forms on land.

On the left is shown the relative number of living organisms on the land and in the sea against the geological time scale in the middle and some major events are shown on the right. Today is the top line and the time before the Cambrian at the bottom is referred to as the Precambrian.

Similar to the extinction event that markedly reduced the number of dinosaur species some 65 million years ago [mya] the Permian period ended with 95% of the known species from that time becoming extinct, they do not appear in the Triassic period’s fossil record.

Life emerges over long spans of time