Answer:
about 252 to 541 million years
Explanation:
To the west the Great Valley, the Valley Ridges, and the Appalachian Plateau (including the Alleghenies) are characterized by the second type of rocks, sediments of Paleozoic age (i.e., about 252 to 541 million years old).
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What is the biggest obstacle to traveling by boat on the Congo River?
A.
the many cataracts
B.
the unusual path of the Congo River
C.
shallow areas due to drought
D.
the river's narrow width
The biggest obstacle to traveling by boat on the Congo River is A. the many cataracts
The numerous cascades on the Congo River are the main challenge for boat passage. Navigation on the Congo River is challenging and dangerous due to a number of strong cataracts, or rapids and waterfalls. The hills and troughs in the riverbed that force the water to flow quickly across them are what generate these waterfalls.
On the Congo River, there are a total of seven major cataracts that make navigation extremely difficult and demand that boats be unloaded and portaged around. There are also shallow places brought on by the drought. Because of the ideal growing conditions provided by these shallow locations, the water plants flourished, producing troublesome obstructions for the boat.
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Write a general statement that could be used to determine if other mass extinctions have occurred in Earth’s history. Explain why your statement would is appropriate. 2-3 Sentences.
Answer:
Explanation:
The most appropriate example is the extinction of the dinosaurs. All sorts of theories were put forth. Most think there was a dramatic change in the environment, a change that left no time for the dinosaurs to adapt to that change.
Whatever happened, an asteroid, volcanic eruptions, or something else, whatever you propose has to explain why birds and mammals survived.
So whatever occurred, it had to be dangerous to land animals, but not those who flew or those who could think well enough to avoid whatever was happening around them.
That said, I would propose that it was a virus that was not air born and the genetic make up of mammals could avoid the harmful effects of the virus.
I would propose that this is the only explanation that works. Perhaps the makeup of the blood could not adapt to the extinction. The blood of a dinosaur might not have included very powerful neutrophils (which fight disease).