Like all the inner planets, Mars and Earth have large cores. The solid core of Mars is takes up just over a third of the planet's diameter. Earth's core takes up over half of Earth's diameter.
The mantles of both planets are rocky. The Martian mantle is just under two-thirds of the planet's diameter. Earth's mantle is a little less than half of its diameter. Both Mars and Earth have thin crusts.
Both Mars and Earth have thin atmospheres. The atmosphere on Mars is not like Earth's. The Martian air is mostly carbon dioxide. The air on Earth is mostly nitrogen and oxygen.
