Gondwana

by Deb on April 9, 2012

Gondwana

Quick quiz – do you think Australia’s jungles are more like the jungles of Indonesia (directly north) or the jungles of India (several islands away)?

Seeing as there’s no point in asking a question with an obvious answer, you probably got it right by saying India, even if you have no idea why or how. The answer was several hundred million years in the making, an ancient super-continent called Gondwana.

Movement of continents

Nowadays the theory of plate tectonics is considered obvious and non-controversial, taught in schools everywhere as an explanation for such things as volcanoes, earthquakes and mountain ranges as well as continental drift. But it really isn’t that old – when I was in uni I read a paper written in 1984 that was still arguing in favour of land bridges to explain the distribution of animals like marsupials. A last, somewhat embarrassing holdout, yes. But not by all that long. It was only a few decades ago that mapping the sea floor and discovering ocean ridges finally gave continental drift a mechanism.

There’s been evidence for continents being closer together than they are today, such as fossils, plants and the shape of the land, for a very long time. But no-one could explain how light buoyant continents ploughed through dense sea floor. Hence elaborate theories of land bridges, convergent evolution, or even flipping the earth on its side to explain glaciers in the tropics. But with plate tectonics we got a mechanism that could quite literally move the earth and happily tied up reams of fossils, animals, plants and rocks that had been frustrating geographers since they started looking at them.

It’s not that people were too dumb to notice all that evidence or too hidebound to accept a new theory, but land bridges were less ridiculous than breaking the laws of physics. In the end we needed to reframe the question – it wasn’t ‘how can light continents move through dense sea floor?’ but new sea floor being created and pushing out that just happened to carry the continents along with it. As soon as they got a mechanism that worked, the land bridges were abandoned so fast none of you have even heard of them.

Note: The reason land bridges sounded slightly plausible was because there are genuine flooded land bridges such as Beringia and Bass Strait between Australia and Tasmania.

Back to Gondwana

During the Jurassic the super-continent Pangaea split into Laurasia and Gondwana, which included Africa, Madagascar, Antarctica, South America, India and Australia. It went from the south pole to the equator, but the world was warmer then and the climate was fairly mild, even near the pole. It had vast forests of temperate trees, with many dinosaurs, birds and reptiles running through the undergrowth.

Gondwana Breakup

During the Cretaceous the various continents of Gondwana broke apart as shown in the animation and moved to their familiar positions, taking their forests with them. These continued to adapt to local conditions, but the plants and animals found there now show their common origins as variations on the Gondwanic theme. Some examples:

  • Marsupials – These actually first evolved outside of Gondwana, when what is now China was part of Pangaea. They migrated into Gondwana through South America and spread through Antarctica to Australia. Genetic testing shows that all living marsupials have a South American ancestor, and it appears that a single type of marsupial made it to Australia, then evolved into all the different ones we have today.opossum
  • Proteaceae – This includes Australian banksias, macadamias and hakeas as well as South African proteas. There are examples of proteaceae from almost all the Gondwanan lands.banksia
  • Nothofagus – The southern beeches, including species from South America, Australasia and fossils from Antarctica.
  • Passerines – the perching birds are now distributed worldwide, but until the late 20th century their origins and relationships were mysterious. Now molecular genetics and fossils suggest that they evolved in Antarctica and Australia before spreading across Gondwana and then the world.passeriforme

Even tens of millions of years after they separated, the ecology and geology of different regions give us clues to their past, not just the pattern of the present.

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{ 5 comments… read them below or add one }

Laura Oreamuno Echeverria via Facebook April 9, 2012 at 1:05 pm

Exc! I will use this information the easiest way possible with kids in our Around the World Class!!

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Trinity April 13, 2012 at 6:50 am

Your post is timely- we’ve been watching the ABC series on Sunday nights- Australia The Time Travellers Guide- which talks all about this sort of stuff- continental plates, fossils, dinosaurs, and all the climate changes that the earth has had in it’s long history. It’s such an exciting thing to see a well-made documentary about Australia’s ancient history. We’re planning on getting it on DVD once it’s released to show to our little ones when they can sit still to watch it.

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Deb April 13, 2012 at 8:33 am

I admit to a bit of cross-pollination! I’d love to be able to watch it but unfortunately it clashes with our bedtime and exhausted children. My girls are loving the Life series by David Attenborough so we’ll be getting the DVD as well.

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trinity April 14, 2012 at 9:02 pm

Iview is a wonderful thing. You can even set it to save each of the programs in the series. Helpful for when I nod off on the couch:)

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Deb April 14, 2012 at 9:16 pm

It’s a bit sad – for a blogger, social media lover and owner of many electronic gadjets, I’m also a bit of a technophobe. That’s something I turn over to my husband to organise.

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