In what way are ancient egyptian hieroglyphs like letters in the english alphabet?

They are similar because:
1) both are writing systems that code language: that is, anything said in a language can be written with them and they can be read aloud

2) some of the hieroglyphs refer to meaning, but some to sounds - just like letters

3) also, our alphabet actually comes from the Hieroglyphs - though the Greek script.

The one that most represents the earths mantle would be the skin since the mantle is the upper part of the earths depths which is just like the skin of an apple.