Answer to Question 1
ANSWER: One might imagine that an asteroid striking Earth would create a big hole in the ground with a shape dependent on the incoming angle of the object. However, the incredible velocity, and therefore the energy, of the impactor requires that it explode violently on impact. The effect is more like a missile being fired into a sand surface. It blasts a nearly round hole regardless of the impact. If the impactor is large enough, the explosion violently compresses material in the bottom of the crater, accelerating it to speeds of a few kilometers per second and ejecting material outward at hypervelocity. The center of the crater rebounds rapidly to form a central cone; that cone and the outer rim almost immediately collapse inward to form a wider but shallower final crater. Impact craters provide evidence about the size and date of past impacts and also help us speculate about the damage those impacts would have caused.
Answer to Question 2
ANSWER: When small pieces of rock from space enter the atmosphere at high speeds, friction with the air molecules heats the surrounding air to white-hot incandescence, forming meteors, or what we sometimes call shooting stars. When a large rock enters Earth's atmosphere, it heats up due to friction with the air and forms a fireball that glows for a period of time before it either disintegrates or survives to strike the Earth. When an object is large enough to survive its passage through the atmosphere without burning up and colliding with Earth, it is called a meteorite.
Comet Tempel 1 67 seconds after colliding with the Deep Impact probe.
Meteor Crater
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Correlates well with global temperature prior to the impact of GHG emissions