What significant event marks the end of the Noachian Period on Mars?

The end of the Noachian Period on Mars is significant due to a transition in the planet's geological and climatic history. This period is characterized by extensive heavy cratering, which reflects a time when the surface was bombarded by asteroids and comets, leading to the formation of many craters. The end of the Noachian is typically marked by the decrease in heavy crater impacts and the commencement of more distinct geological processes.

The evidence pinpointing the transition away from the Noachian is based on both the number of craters and the shift to a period where volcanic activity and erosion became more prominent. While other options may describe various features or phenomena associated with Mars, they do not represent a definitive end marker for the Noachian Period. For instance, while Olympus Mons, the largest volcano in the solar system, is a notable feature of Mars, its formation does not align specifically with the end of the Noachian. Similarly, subsurface ice melting and the onset of giant dust storms represent processes and phenomena that occurred later or concurrently but do not themselves define the boundary of this particular geological period.