Protoplanetary disks are collections of gravitationally bound gas and dust where stars and planets are formed.

(a) what are the 4 main types of materials that compose protoplanetary disks? and what are their typical relative abundances?

(b) why did the terrestrial planets form close to the sun, and gas giants form far away from the sun?

(c) how do we reconcile the existence of "hot jupiters," which are commonly found around distant stars, with nebular theory?

it is very hard for the climatologists to precisely predict how will the global temperatures be changing so there's lots of models, some of which differ significantly, this is due to multiple factors, and probably the most important is the human activity.

humans have been a key factor in climate change around the globe since the start of the industrial revolution, and in the past few decades the consequences are becoming more obvious. there's lots of emission of pollutants in the atmosphere as well as changing the environment on the surface itself, so it's really hard to predict how will that go in the future because there's some countries that are reducing the damage and are going towards green energy, while others are stubbornly continuing with pollution and damages to the environment.