Earth’s atmosphere has layers of gas surrounding it, our planets atmosphere is retained by it's gravity.
Earths Atmosphere contains;
78% Nitrogen
21% Oxygen
0.97% Argon
0.04% Carbon Dioxide
This mixture of gas is known for as air.
I would say it would b D. Irish moving to America during the Potato Famine, as it wasn't necessarily forced, but they went of their own free will
Hey there! I'm happy to help!
The Fertile Crescent is basically where human civilization started. It stretches from Mesopotamia and across the Mediterranean coast to Egypt. Early civilizations depended on agriculture. To make agriculture, you need a river because it is a good water source to help grow your crops.
If you look at the map I have provided below, you will see that there are tons of rivers. This would make it very easy for settlers to grow crops. This means that sea tides and eroding mountains aren't the answer. I don't think the rivers were flooding and natural canals is an oxymoron because canals are artificial waterways, but this all should give you and idea.
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Aquifer is simply ground water and one of the best sources of quality water for irrigation and home use.
aquifer can be polluted like any other sources of water.
This can happen when pollutants such as random gas, oils,and chemicals get into the aquifer thus contaminating it.