Which is the correct order of layers of the earth from outside to inside?

Question 1
Which is the correct order of layers of the earth from outside to inside?
- Crust, mantle, outer core, inner core
- Mantle, outer core, crust, inner core
- Outer core, inner core, mantle, crust
- Crust, outer core, mantle, inner core
Question 2
Which layer of the Earth is primarily composed of iron and nickel, and is the source of the planet's magnetic field? Explain why this layer is crucial to sustaining life on Earth.