Answer:
Mass determines how hot the stellar core gets in response to gravitational contraction, and since the rate of nuclear burning is very sensitive to temperature, a star's mass determines the energy production rate and whether/when gravitational contraction can lead to explosive release of energy
Explanation:
The correct answer is - Americans moved west in the 1800's because people wanted to get a fresh start and wanted to be able to buy their own land, as well as to try new economic possibilities, such as farming and gold mining.
In the 1800's the situation in the west started to stabilize and be much more attractive for people to move in. The problems with the native American populations were almost totally put under control so the safety issue was mostly resolved. Also the government had policies to give free land or for very small amount of money as to attract people to move there and thus have the demographic basis for implementing their rule more efficiently. For lots of people, mostly the ones from the lower class, this was seen as a golden opportunity and they used it as quick as possible.
Answer:
It took climate change, fertile river valleys, domestication of crops and animals so that the hunter-gatherers became sedentary farmers.
Explanation:
Initially, all humans were hunter-gatherers. This was due to multiple reasons, with one the biggest one probably being the climate which was not enabling good conditions for the hunter-gatherers to transform their lifestyle. All other conditions needed were stopped because of the climate conditions, so humans had to do what they could to survive in those conditions.
About 10 years ago though the bad climate conditions ended, or rather the Ice Age ended. This resulted in a much warmer climate, which in turn created much more water bodies like rivers and lakes, much more vegetation, and they contributed to the creation of much more fertile soil.
With these conditions in place, the humans quickly saw that there is huge potential in some plants and animals, so they started to farm them, select the ones with the best characteristics, and gradually producing enough food for themselves. With the food problem solved, humans didn't have the need to wonder around all the time, so they started abandoning the hunter-gatherer lifestyle and started settling in one place.
In simple terms, chlorophyll makes a leaf look green because it reflects only green light.
Answering in a more detailed fashion, chlorophyll is a pigment. As a pigment it absorbs some wavelengths of visible light, (red, orange, yellow, green, blue, indigo, and violet are the colors of visible light), while reflecting others. In specific, chlorophyll absorbs all other colors of light but green, which it reflects. It is this reflection of green light that cause a leaf to appear green.
destroying one part of the ecosystem affects every other part of it .
