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How long have these organismsbeen living on Earth?

cockroachnautilus

magnolia

dragonfly

caddis fly

shark

lungfish mammal

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How long have these organismsbeen living on Earth?

cockroachnautilus

magnolia

dragonfly

caddis fly

shark

lungfish mammal

Extinctions

and possibly here

Extinctions are relativelycommon in the geologicalrecord. They may be dueto single events, like large impacts, or to a combinationof effects like changes inworld climate and volcanism.

However, as you can see, life goes on!

Apatite

Apatite is calcium phosphate.These crystals are from Cornwall in the U.K.: thelargest crystal is about 4cm long.

DNA

DNA is a very large molecule, made up of simpler units repeated billions of times.

The sides of the “ladder” are made of alternating sugar and phosphorus units.The rungs of the “ladder” are made up of pairs of bases. There are four types of base to choose from, and the sequence of these 2.85 billion pairs forms the code for life.

If you could make a model of DNA with the rungs one centimetre apart, the stretched-out coil would stretch THREE-QUARTERSof the way round the Earth, or from Canberra to Brasilia in South America AND BACK!

Archaean

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Cyanobacteria, single-celled organisms still livingtoday, flourished in shallowwater. They grow in layersto build up sheets, domes and cones by trapping sediment grains or by depositing limy material, making the stromatolites familiar to us in WA. The world’s oldest stromato-lites are found at NorthPole, in the Pilbara.

Proterozoic

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Ediacaran fossils are found in South Australia andin other places world-wide. They are all extinct species but despite their strange appearance, somecould have been the ancestors of life on Earth today.

A goblet-shaped fossilfrom around 560-550 million years ago: up to 5cm long, it has one of the earliest known mineralised skeletons.

A metre-long fossilwith a mineralisedskeleton from around 560-550 million years ago: it may be related to corals or sponges.

These trails on 1.9 billion year-old sands from the Stirling Ranges are thought to have been made by soft-bodied animals!

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Cambrian

Archaeocyathids, small (8-10cm) and vase-shaped,were filter-feeding creatures which formed great reefs.

Trilobites were segmentedmarine creatures, up to 50cmlong which were swimmers, burrowers and bottom dwellers.

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Graptolites were colonialanimals with horny skeletons,growing to about 10cm long.

Ordovician

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Silurian

Eurypterids werecarnivorous marine“sea scorpions”, the first creatures known to walk on land.

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Devonian

Lungfish

First sharks

Armoured fish

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Carboniferous

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Permian

Trilobites declined in numbers during the Carboniferous andbecame extinct by the end ofthe Permian.

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Triassic

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Jurassic

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Cretaceous

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Tertiary

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Cenozoic animals

These now extinctanimals are of Neogene (late Cenozoic) age: some date back to around 15 million years ago.Some may have co-existed withAborigines.

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Neogene: Pleistocene

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HoloceneDon’t forget thatthe Holoceneincludes us!