Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: The scientists used geologic dating techniques on seafloor rocks. They found that the youngest rocks on the seafloor were at the mid-ocean ridges. The rocks get older with distance from the ridge crest. The scientists were surprised to find that the oldest seafloor is less than 180 million years old. This may seem old, but the oldest continental crust is around 4 billion years old. Answer: mid-ocean ridges
A:
Scientists found that the youngest rocks on the seafloor were where?