Given a scientific question, generate a correct answer to it.
--------
Question: What were the first living things to evolve on earth?

Answer: prokaryotes

Question: Both fats and oils are made up of long chains of carbon atoms that are bonded together. what are these chains called?

Answer: fatty acids

Question: What is the outer layer of an axon that acts like a layer of insulation, similar to the plastic that encases an electrical cord?

Answer:
myelin sheath