Question by dez: What does the presence of limestone indicate about an area’s ancient history?
What does the presence of limestone indicate about an area’s ancient history?
A. The land used to be an area of many volcanoes.
B. Glaciers covered the land at one time.
C. The land used to be much higher.
D. Shallow seas once covered much of the land.
Best answer:
Answer by Rishab J
D. Shallow seas once covered much of the land.
What do you think? Answer below!
Limestones indicate shallow warm seas at the time of deposition. Lime, CaCO3 is one of the odd substances that has its maximum solubility at low temperatures. As the water temperature goes up the solubility goes down and so the lime is precipitated- dropped out of solution. Shallow seas are more easily warmed by sun light and do not have much mixing from cold water at depth.
(ANother note. Limestones also usually form a some distance from the coast. Near the coast the denser sediments drop out, the soluble lime is carried farther away from shore. This tends to show the original was shallow to a considerable distance from shore.)
None of the above necessarily apply but the expected answer will be d.
The reason it’s not necessarily correct is as follows. While limestone is usually the result of deposit of lime sediment in near coastal waters, that doesn’t apply in all cases. It can also build up in terrestrial bodies of water such as lakes. The Purbeckian Limestone in Dorset, England, for example, is largely composed of non-marine deposits. Nevertheless, it’s definitely limestone. In fairness, such cases are exceptions to the general rule.