Question

what evidence suggests that asteroid and meteoroid impacts were common in early earth history?
abundance of mammalian fossils
presence of large impact craters and iridium in rock layers
widespread coral reef formations
layers of volcanic rock

Explanation:

• Abundance of mammalian fossils: Mammals evolved much later in Earth's history, long after the period when asteroid/meteoroid impacts were most common. So this is not relevant evidence for early Earth impacts.
• Presence of large impact craters and iridium in rock layers: Iridium is rare on Earth's crust but common in asteroids and meteoroids. Large impact craters are direct physical evidence of impacts. This combination is strong evidence for past asteroid/meteoroid impacts.
• Widespread coral reef formations: Coral reefs are related to marine ecological and geological processes (like carbonate deposition in shallow - water environments) over time, not to asteroid/meteoroid impacts.
• Layers of volcanic rock: Volcanic rock layers are related to volcanic activity (magma extrusion, etc.), not directly to asteroid/meteoroid impacts (though impacts can sometimes trigger volcanic activity, but the rock layers themselves are not evidence of impacts).

Answer:

Presence of large impact craters and iridium in rock layers