For an explanation, see the main splats page
SPLATS about geological history
The principles of geological history
- The earth changes as time goes by: mountains are uplifted and eroded away, continents move, the magnetic poles move, volcanoes erupt and are eroded.
- All of geology is consistent with standard processes applying over the standard geological time scale lasting some 4.6 billion years: there are no exceptions.
- One explanation of the earth is based on uniformitarianism. One explanation of the earth is based on catastrophism: neither is a perfect fit to the facts.
- Land forms have been shaped by factors such as weathering and erosion that we can see operating today: this is the principle called uniformitarianism.
- One aspect of geological history is geomorphology, which studies the way in which geological forces that we see today have shaped the major landforms.
- Uplift of rocks is followed by erosion, but equally, erosion is followed by isostatic uplift, since the crust of the planet floats on the mantle.
- Erosion changes the surface of the planet, by wearing down hills and mountains, and by cutting new valleys, both with ice and with water carrying sediment away.
- A gap in the geological record may be an unconformity, where one set of beds has been tilted, folded and eroded, before being overlain by later sediments.
- A gap in the geological record may be represented by a disconformity, where the beds above and below a gap are in alignment, bet deposition stopped for a while.
- Landforms may be determined by the underlying rocks, since more resistant beds will tend to remain, forming ridges that must be bypassed by rivers and glaciers.
- The formation history of a sedimentary rock aeolian or alluvial deposits as may often be found in the rock, either in structures, or in the fossils
- Wind erosion causes dust storms and sandhills, and given the right winds, has even been known to move fine sediments from one continent to another.
- Ice or glacial erosion creates unusual landforms such as moraines, which allow us later to recognize the influence of ice in shaping the landscape.
- Glacial valleys have a different shape from those cut by water erosion, because the grinding action of the valley-filling flowing ice makes a U-shaped valley.
- The ratios of stable isotopes in fossils provide good evidence of past climates because they generally give an indication of past temperatures.
- Tree rings provide good evidence of past climates, because the tree rings formed in good years are thicker. This is called dendroclimatology.
- We can obtain evidence of past climates from fossil data of many sorts, anything which varied with the conditions such as temperature at the time.
- We can gain evidence about past climates from palynology, the study of pollen grains, because the grains are distinctive to a particular species.
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