Final answer:
Venus exhibits a rocky surface with igneous, primarily basaltic, composition, bolstered by radar maps revealing a geologically active history. Its thick atmosphere and mixed chemical composition are similar to Earth's, with evidence of past plate tectonics.
Step-by-step explanation:
The evidence points to Venus's rocks primarily being igneous, especially basalts, which suggests a transformation from a potentially earthlike state to its present condition. Radar maps of Venus expose a planet with a surface mostly unchanged by erosion or sediment deposition, due to the lack of water and ice, and low surface wind speeds. This has left the surface features intact, indicating hundreds of millions of years of geological activity.
Analyzing the planet's greenhouses effect, due to its thick atmosphere, and its chemical composition falling between the models for a pure iron and a pure rock planet, scientists infer a mixed chemical composition similar to Earth's. Moreover, geologic evidence hints at plate tectonics in Venus's past, analogous to those on Earth.