Tutor profile: Andy R.
How can you tell if a sandstone formed in a desert as opposed to a beach?
Deserts, being a system dominated by wind transportation, only fine grained sand would make up the stone. Finer grains would be blown away, while coarser grains would not be entrained by the weaker winds. A beach sandstone would be more poorly sorted. Desert sandstones might also have such features as larger crossbeds, megaripples, and tafoni patterns.
Subject: Earth Science
Where is oceanic crust the oldest? Why is this the case?
The oldest oceanic crust is found right before oceanic-continental plate boundaries. Since oceanic crust spreads outwards from mid-ocean ridges, the further the basalt has been pushed from it origin, the older it is. Basalt is the subducted under the continental crust and recycled in the mantle.
What is punctuated equilibrium in regards to evolution? List evidence that supports this theory.
Punctuated equilibrium explains how species change gradually over a long period of geologic time. A small change will occur rapidly and then the species will reach a level of stability before the next rapid change occurs within future generations. These rapid changes are small and do not seem obvious until the whole evolutionary line is viewed as a whole. Punctuated equilibrium is often supported by the fossil record and biostratigraphy.
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