In 1974 we transmitted a message toward the globular cluster M13 which is 21,000 ly away. What is one reason that this object was probably not ideal for sending a message to?
A) it is so far away that we will probably have stopped communicating before we receive and return signal
B) globular clusters contain young, high mass stars with insufficiently long main sequence lifetimes and hence are unsuitable places for life
C) the message will be absorbed by interstellar dust before it reaches the cluster
D) globular clusters contain, old, low mass stars with fewer heavy elements and hence are not ideal places for life
Question 2
Given the Earth's larger size and strong gravity, the Earth's surface should have more impact craters than the Moon. However, it has very few. Why is this?
A) the Moon acted like a shield, protecting the Earth from most impacts
B) the Earth's surface was almost completely molten during the Hadean Eon so no impact craters were formed
C) almost all impacts occurred in the oceans so no impact craters were formed
D) geological processes like plate tectonics, volcanism, and erosion have erased them
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