Much speculation about the geological history of Venus continues today.The surface of Venus is not easily accessible because of the extremely thick atmosphere (some 90 times that of Earth's) and the 470 °C (878 °F) surface temperature.The most important elevations are in the mountain chains that surround Lakshmi Planum: Maxwell Montes (11 km, 6.8 mi), Akna Montes (7 km, 4.3 mi) and Freya Montes (7 km, 4.3 mi).Despite the relatively flat landscape of Venus, the altimetry data also found large inclined plains.Nevertheless, there is substantial evidence that the Earth and the other bodies of the Solar System are 4.5-4.6 billion years old, and that the Milky Way Galaxy and the Universe are older still.The principal evidence for the antiquity of Earth and its cosmic surroundings is: Spontaneous breakdown or decay of atomic nuclei, termed radioactive decay, is the basis for all radiometric dating methods.
There are shield and composite volcanoes similar to those found on Earth.
No landforms indicative of past water or ice are visible in radar images of the surface.
The atmosphere shows isotopic evidence of having been stripped of volatile elements by offgassing and solar wind erosion over time, implying the possibility that Venus may have had liquid water at some point in the distant past; no direct evidence for this has been found.
The altimetry experiment of Magellan confirmed the general character of the landscape.
According to the Magellan data, 80% of the topography is within 1-kilometre (0.62 mi) of the median radius.