Part C
Geology of Ancient Earth
The Hadean Eon was referred to as "the rocless eon" for a reason, as the older the rocks, the harder they are to find. The oldest known earth material Hadean in age is represented by tiny zircon crystals (4.4-4.0 Ga) incorporated into younger Archean sedimentary rocks in a remote area of western Australia (see Figure 8-8). These tiny relict grains represent the existence of some Hadean rock that was either eroded away or destroyed or has not yet been found. To date, evidence of geology this ancient has not been discovered anywhere else on Earth. The oldest actual rocks and rock outcrops exist in the Slave province of northwestern Canada (see Figure 8-8). These exposures date to around 4 Ga and represent the oldest intact rock exposed on the planet.
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Figure 8-8. The oldest known earth materials and exposed bedrock. At left, a microscopic 4.4 Ga zircon crystal from the Jack Hills, western Australia (courtesy J. Valley). |
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Geologic Map of Western Australia
The western part of Australia contains a record of some of Earth's earliest geologic history, including rocks that represent Archean cratons and greenstone belts.
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Figure 8-9. Archean rocks and life forms from western Australia. At left, an outcrop of the 3.4 Ga Marble Bar Chert, Pilbara Craton (courtesy NASA). |
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Quiz Me! questions C21 through C33 refer to the Geologic Map of Western Australia (see the PDF link below).
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Geologic Map of Western Australia |
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This is a big map, so it may take a minute to load. You'll be doing some panning and zooming when reading this map. |
Main Tectonic Units of Western Australia
Explanation & Correlation of Map Units
Geologic Map
Geologic Map of the Sierra Madre and Medicine Bow Mountains
Archean rocks of the Wyoming Craton are locally exposed in the mountains of the northern Rocky Mountains, including exposures in the Sierra Madre Mountains, Medicine Bow Mountains, Wind River Range, etc.
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Figure 8-10. The Medicine Bow Mountains in Wyoming. At left, the view from the Medicine Bow Peak trail. At right, quartzite boulders below the steep slopes of the Snowy Range. |
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Quiz Me! questions C34 through C45 refer to the Geologic Map of the Sierra Madre and Medicine Bow Mountains, Wyoming (see the PDF link below).
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Geologic Map of the Sierra Madre and Medicine Bow Mountains, Wyoming |
List of Map Units & Correlation of Map Units
Geologic Map