Book contents
- Frontmatter
- Contents
- Colophon
- Preface
- Acknowledgements
- Maps
- Units of measurement and abbreviations
- 1 Geology: An Australian perspective
- 2 The Earth: A geology primer
- 3 Telling geological time: The great canvas
- 4 The cratons: Building the core of Precambrian rocks
- 5 Mountain building: Paleozoic orogenic rock systems
- 6 Warm times: Tropical corals and arid lands
- 7 Icehouse: Carboniferous and Permian glaciation
- 8 Mesozoic warming: The great inland plains and seas
- 9 The birth of modern Australia: Flowering plants, mammals and deserts
- 10 Fossils: The Australian record of past life in context
- 11 The land stirs: Volcanoes and the eastern highlands
- 12 The outline and submerged terrace: Building the continental shelf and coastlines
- 13 The coral reefs: Unique parts of the continental shelf
- 14 Patterns of change: Cycles in Australia's journey
- Epilogue
- Sources and references
- Index
- References
4 - The cratons: Building the core of Precambrian rocks
- Frontmatter
- Contents
- Colophon
- Preface
- Acknowledgements
- Maps
- Units of measurement and abbreviations
- 1 Geology: An Australian perspective
- 2 The Earth: A geology primer
- 3 Telling geological time: The great canvas
- 4 The cratons: Building the core of Precambrian rocks
- 5 Mountain building: Paleozoic orogenic rock systems
- 6 Warm times: Tropical corals and arid lands
- 7 Icehouse: Carboniferous and Permian glaciation
- 8 Mesozoic warming: The great inland plains and seas
- 9 The birth of modern Australia: Flowering plants, mammals and deserts
- 10 Fossils: The Australian record of past life in context
- 11 The land stirs: Volcanoes and the eastern highlands
- 12 The outline and submerged terrace: Building the continental shelf and coastlines
- 13 The coral reefs: Unique parts of the continental shelf
- 14 Patterns of change: Cycles in Australia's journey
- Epilogue
- Sources and references
- Index
- References
Summary
What do we know of the origin and age of the Earth and how it was organised in its formative stages? What do we know of climate in the very distant past? When did life first appear and what was it like? Australian rocks have much to contribute in answering these questions. The oldest rocks tell us that the continents, oceans and atmosphere are of great antiquity but have changed remarkably with time. Plate tectonics and its consequences are also of great antiquity and had a controlling influence on shaping the crust to form the original nucleus of Australia in very deep time.
THE ORIGINAL EARTH
Formation
The Earth's surface has been comprehensively remodelled from its initial state as it has evolved through time, with new rock systems replacing and covering those of greater age. As a consequence, the early stages of the Earth's development are poorly known, through progressive lack of evidence backwards to the beginning. The most accepted scientific theory is that following the big bang and the origin of the universe, and after the contraction of the matter that formed the Sun, a huge rotating disc of dust and gas, spread across billions of kilometres of space, was left behind. This disc of debris gradually collapsed due to gravity, coalescing into a series of variously sized lumps, or planetesimals. The planetesimals, which ranged in size from a few metres to Mars-like proportions, then accreted by gravity over a period estimated to have been 29–100 million years. They aggregated to form spinning balls of rock, gas and ice – the planets – and the Earth is one of them.
The most widely accepted hypothesis is that the Moon originated from a collision between the Earth and a similar-sized body, with the mass now forming the Moon ejected as a consequence. Moon rocks can be matched with igneous rocks of the Earth and are between about 4.5 and 3.1 Ga old, overlapping substantially with the age of the early Earth's rocks. The early Earth and Moon were bombarded with meteoroids, asteroids and comets, probably the debris left from formation of the Solar System.
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- The Geology of Australia , pp. 85 - 108Publisher: Cambridge University PressPrint publication year: 2016