The areas of similar figures are proportional to the square of their linear scale factor. If Mars is 1/2 the diameter of Earth, its total surface area is (1/2)² = 1/4 that of Earth.
That is, the land area of Mars is 25% of the total area of Earth.
The land area of Earth is 1-70% = 30% of the total area of Earth. 30% is more than 25%.
