With reference to the internal structure of the Earth, consider the following statements:

1. The mean thickness of the oceanic crust is about 5 km, while that of the continental crust is around 30 km.
2. The mantle extends from the Moho discontinuity to a depth of approximately 2,900 km.
3. The lithosphere comprises the crust and the entire mantle.
4. The outer core is liquid, whereas the inner core is solid and the core is composed mainly of nickel and iron.

Which of the statements given above are correct?