It's some change in the conditions around the organism, which the organism can detect and respond to. A change in temperature, more light, or something physically poking the organism are examples.
Answer:
Graptolites lived from the Cambrian Period, about 510 million years ago, disappearing in the Carboniferous Period, around 320 million years ago.
hope this helps!
Don't pollute the Earth.
Don't need gas.
