Question

what are believed to have caused the steep cliff - like north and south ridges that stretch over mercurys surface?

an impact from a moon - sized meteorite

early tectonic activity and tidal forces

giant solar flares when the solar system was formed

chemical reactions from its volatile atmosphere

Explanation:

Mercury's steep cliff - like ridges are thought to be the result of early tectonic activity and tidal forces. Tectonic activity can cause the crust to deform, and tidal forces (due to the gravitational pull, especially from the Sun) can also contribute to the shaping of the planet's surface features. An impact from a moon - sized meteorite would likely create a large crater rather than long - stretching ridges. Giant solar flares during the solar system's formation would have more of an impact on the atmosphere and magnetic field rather than creating such surface features. Mercury has a very tenuous atmosphere, and chemical reactions from a volatile atmosphere would not be the main cause of these prominent surface ridges.

Answer:

early tectonic activity and tidal forces