Which internal heat source still generates heat within the terrestrial worlds today?

Astudent creates a model of a closed ecosystem by filling a glass tank half full with water, then adding 10 snails and two small aquatic plants. the next day, all the snails are dead. what is the most likely cause of their death?

Often called simply "velocity," this is the velocity of an object at a particular moment in time.

What was the first instrument to ever record an earthquake?