The Unique Australian Environment Ashleigh Bartlett.

The Unique Australian Environment

Ashleigh Bartlett

Approximately 250 million years ago the world was made up of one ‘Supercontinent’ containing all the separate continents that we have now. This supercontinent was called Pangaea, coming from the Greek language, pan meaning ‘entire’ and gaia meaning ‘world’. Due to there only being one land mass, there was only one enormous ocean, this was called Panthlassa.

There is much evidence supporting Pangaea’s existence. Many fossils or similar or identical species of plants and animals has been found in continents which are now very far apart. Geological trends in continents great distances apart also confirms the existance of Pangaea. Glacial deposits from the carboniferous period have also been found on several different continents that at one stage may have been connected.

Pangaea

The Breakup of PangaeaThe breakup of Pangaea occurred in three stages.The first stage began in the Early-Jurassic Period, when

Pangaea began to rift from rift from oceans on the east and west, this led to the formation of supercontinents ‘Gondwana’ and ‘Laurasia’. This formed The North Atlantic Ocean.

The second stage began in Early-Cretaceous period, when Gondwana separated into multiple different continents. These new continents were South America, Africa, Australia, India and Antarctica. These continents continued to drift slightly, causing the formation of the South Atlantic Ocean, Coral Sea and Tasman Sea.

The final stage occurred in the early Cenozoic Period, when North America/Greenland broke free from Eurasia causing Laurasia to split. This caused the formation of the Norwegian Sea. Australia then split from Antarctica and moved rapidly upwards.

GondwanaGondwana (also known as

Gondwanaland) was the name given to the southernmost supercontinent after the split of Pangaea. After the split from Laurasia, Gondwana drifted to the south. Gondwana consisted of most of the land masses in the Southern Hemisphere today, as well as Arabia and the Indian Subcontinent which have moved entirely into the Northern Hemisphere.

Gondwana was made up of South America, Africa, Arabia, India, New Guinea, Antarctica and Australia.

LaurasiaAfter the split of Pangaea, the

Northernmost supercontinent was named Laurasia. It is believed that the subcontinents that make up Laurasia, were once connected before the formation of Laurasia. This was due to the breakup of supercontinent Rodinia about 1billion years ago. This was called Proto-Laurasia, to avoid confusion with Laurasia. The second breakup was due to plate tectonics, continental drift and seafloor spreading.

Timeline • Jurassic Period (208-144 million years ago)• 208 million years ago• continental drift, Pangaea begins to break apart into Laurasia and Gondwana toward the end of the Jurassic

• Cretaceous Period (144-66 million years ago)• 100 million years ago further continental drift, begins formation of modern continents 90 million years ago• 88 million years ago• Madagascar splits from India

• CENOZOIC ERA (66 million years ago to the present)

• extinction of the dinosaurs and other land animals heavier than 25 kg.• 62 million years ago• 34 million years ago separation of Antarctica from South America, begins formation of Antarctic ice 6 million

years ago• Separation of Atlantic Ocean and Mediterranean Sea by geologic activity Messinian Salinity Crisis--

evaporation of Mediterranean Sea climate change, drier conditions, loss of forests in Africa• 5.8-5.2 million years ago• 5 million years ago significant closing of gap between North and South America, increasing salinity of the

Atlantic, cooler and drier weather in Africa 3.5 million years ago rise of Isthmus of Panama, Pacific and Atlantic Oceans separated, further salinity increases in Atlantic waters, continuing cooler and drier weather trend in Africa

Cause of the breakupThe surface of the earth is broken into rigid plates, which are 100 to 120

kilometers thick and include a small part of the upper mantle as well as both continental and oceanic crusts. These crusts and upper mantle are often referred to as the lithosphere .

There are 12 major plates as well as numerous smaller ones, which get their names from the regions where they are located. These plates are constantly moving, all at different speeds and in different directions due to the convection currents in the atmosphere. It is believed that the plates move approximately 5cm per year, which over a long period of time causes the large scale movement and breakup of the continents.

Animals in Pangaea

Today, we know migration of the animals across Pangaea is documented by fossil remains found in both the northern and southern hemisphere. Fossils of Mesosaurus, a marine reptile, are found in deeply southern South America, Antarctica and South Africa, where they could not survive in today's climate.

When Pangaea broke, terrestrial animals were isolated. Some species were further isolated to the continents of Antarctica, Africa Australia and South America. Each species would travel different evolutionary paths based on the changes in the climates on the smaller continents.

Animals on Gondwanaland

The ancestors to modern marsupials, reptiles, birds, amphibians, and many plants such as ginkgoes, cycads, many pines, and flowering plants appear in the fossil record from Gondwana. There were also large numbers of cicadas and earthworms on Gondwanaland.

DinosaursAfter the breakup of Pangaea, dinosaurs roamed freely on

both Gondwana and Laurasia. The characteristics of these dinosaurs differed muchly from the northern land mass and the southern land mass. Dinosaurs evolved to be able to survive in their climate. When Pangaea split there was even spread of most of the dinosaurs across the land. Many of the dinosaurs that could survive on Gondwana could not survive on Laurasia and therefore there was a rapid decline in the numbers of some dinosaur species such as Sauropods. This could be one of the factors of the extinction of dinosaurs. After parts of Gondwana began to break away, the dinosaurs in Australia began to evolve to survive on the isolated land, as a result of this, Australian Dinosaurs were different to any other dinosaur in the world.

Changes to plants & animals

Over time all plants and animals have to adapt to the changing climate conditions. These changes are not sudden but by looking at fossil records, you can see a distinct change from one period of time to another in all plants and animals. Some species of animals survive better in the colder conditions, therefore when the weather heats up the animal needs to find somewhere cooler to live and this is the same with species of animals that prefer the warmer weather. Some species of plants and animals learnt to become more tolerant to the ever-changing weather conditions of Gondwana.

Humans on PangaeaIt is believed that

humans began in Africa and took a southerly route to spread across the world. These humans walked across the land which was once called Pangaea. This diagram shows the migration of the first humans.

Bibliography

www.wikipedia.com , WikipediaSearches; Pangaea, Gondwana, Laurasia, Migration of first humans.www.google.com/images, Google imagesSearches; Unique Australian Environment, Australian Animals, Lizards,

Dinosaurs, Moss, Snakes. http://fajardo-acosta.com/worldlit/timeline-00.htm, World Historyhttp://www.divediscover.whoi.edu/tectonics/boundaries.html, Tectonic Plates

for studentshttp://www.helium.com/items/225078-explaining-pangaea, Pangaeahttp://www.experts123.com, Question and Answer Encyclopediahttp://

animals.howstuffworks.com/dinosaurs/early-cretaceous-period.htm/printable, How Stuff Works

www.encyclopedia.com, Online Encyclopedia