What can scientists learn by studying fossils? i. how the earth's surface has changed over time ii. the appearance of an organism and its structures iii. how species have changed over time iv. how the earth's climate has changed over time

All of the above!

By analyzing the remains of fossilized organisms (such as old animal bones or plants), scientists can approximate what the organism might have looked like and the climate/environment it lived in -- and based on that, they can try to figure out how the Earth's surface has changed over time. Also, they can use the fossil to compare it to creatures that live now to see what has changed in that species over time.

Density because it’s holyyy