How do scientists study the history of life on Earth? A) by ...

[ishan]

How do scientists study the history of life on Earth?
 
  A) by comparing present-day organisms with each other, and assuming past life had mixed traits of present-day organisms
  B) by assuming that life in the past was just like present-day life
  C) by using telescopes to look far away, and thus see what life was like in the past
  D) by studying fossils, the preserved remains of past organisms

Question 2

Explain how the resonance among Io, Europa, and Ganymede makes their orbits slightly elliptical.
 
  What will be an ideal response?

[millet]

Answer to Question 1

D

Answer to Question 2

For every orbit that Ganymede completes around Jupiter, Europa completes exactly two orbits and Io completes exactly four. Therefore, all three planets line up for every orbit of Ganymede, and Io and Europa line up twice each Ganymede orbit. The gravitational tugs from their sister moons add up over time, and these tugs are always in the same direction. Therefore, the moons' orbits become slightly elliptical over time.

[ishan]

Wow, this really help

[alvinum]

Thanks for the timely response, appreciate it