Complex sentence: With an area of 13.1 million km² (5.1 million square miles), Siberia makes up roughly 77% of Russia's total territory and almost 10% of Earth's land surface (148,940,000 km²).
Split into simpler sentences: With an area of 13.1 million km² (5.1 million square miles), Siberia takes up roughly 77% of Russia's total territory. Siberia covers almost 10% of Earth's land surface (148,940,000 km²).