Author Question: Which stage of planetary development has all but eliminated much of Earth's surface history? a. ... (Read 121 times)

azncindy619 · **on:** Jul 27, 2018

Which stage of planetary development has all but eliminated much of Earth's surface history?

a. flooding
b. cratering
c. differentiation
d. bombardment
e. slow surface evolution

Question 2

Briefly discuss the gas-stars-gas cycle.

What will be an ideal response?

nikmaaacs · **Reply #1 on:** Jul 27, 2018

Answer to Question 1

e

Answer to Question 2

During a star's lifetime, it fuses hydrogen into helium and helium into carbon. If it is more massive, it also creates heavier elements, up to iron, by fusion, and even heavier elements during a supernova event. When the star ends its life as a planetary nebula or in a supernova explosion, it disperses these elements into the interstellar medium. The interstellar medium thus gains these heavier elements and has a smaller proportion of hydrogen but a larger proportion of heavier elements than it did before. The newly added material to the interstellar medium cools, forms molecular clouds, and then forms new stars, which are now made out of material in the interstellar medium with a larger heavy element content. These stars evolve and the cycle continues.