Timeframe: 4,600–2,800 Ma*, Hadean & Archean
*Ma = millions of years ago
This theme covers the earliest time of the earth – from its formation as a molten blob of metal and rock heated by millions of meteor hits, to a stable planet with the beginnings of oceans and a crust. There are very few rocks known from the Hadean, being in the oldest parts of Greenland, Canada and Western Australia. The asteroids still in the solar system are older than the earth. The oldest dated object from Earth is a tiny crystal remnants (zircon grains) in later rocks, particularly those of the Jack Hills Conglomerate.
In the early Archean (starting 4,000 Ma), the foundations of the future continent of Australia were laid with the formation of the Yilgarn, Pilbara, Gawler and North Australian Cratons. Areas of the crust from this time, particularly those in western Australia, show that the dynamics of the hot early earth were different from those today. Current theories suggest that the higher heat of the early earth was able to drive tectonics in a vertical direction instead of the horizontal movement we see today. Volcanics were also much more vigorous and erupted lavas which had a composition closer to that of the mantle (komatiites) than we see to today, as well as the basalts that characterise most current volcanoes.
Rocks in this theme show:
- the old cores of the continent,
- a different hotter earth.
- examples of gneiss,
- examples of greenstones (metamorphosed basalts and komatiites) and
- ancient sediments.
Key resources from the Archean are gold from Kalgoorlie, nickel from Kambalda, lithium from Greenbushes (all in Western Australia).
- 3,800 Ma – end of ‘Late Heavy Bombardment’ by huge meteorites
- 3,480 Ma – earliest signs of life; stromatolites in Dresser Formation, North Pole Pilbara
- No Early Earth rocks are on display in the garden at the moment. We are looking forward to getting our first exhibit in this theme.
- North Pole Barium ore, Pilbara, WA, 3,481 Ma
- Marble Bar Chert Member, WA, 3,460 Ma