Gravity , Explosion
<u>Explanation:</u>
Nebulae are made of dust and gases—mostly hydrogen and helium. The dust and gases in a nebula are very spread out, but gravity can slowly begin to pull together clumps of dust and gas. As these clumps get bigger and bigger, their gravity gets stronger and stronger.
Eventually, the clump of dust and gas gets so big that it collapses from its own gravity. The collapse causes the material at the center of the cloud to heat up-and this hot core is the beginning of a star.
plays the role in skeletal muscle movement
Okay so northern Africa and the Sahara desert is the best example of desertification.
2 ways humans have contributed to that is: 1) pastoral nomadism 2) little to no settlements to increase water supply
how it impacted the environment: so now the environment there is sandy, only organisms adapted for those extreme environment can live there ex. camel, cactus, etc.,
how it impacted quality of life: quality of life diminished, not enough water to sufficiently feed the populations, people live in extreme poverty, people are moving away, and the climate is very dry and hot, pretty much not a place anyone would want to live
http://eden-foundation.org/project/desertif.html
https://www.sciencedaily.com/releases/2017/03/170314111320.htm
Out of the options I would have to say Penetrating Keratoplasty, I am not sure
