How can it be known that Venus does not have plate tectonics?

Question

This answer provides some insight into Venus' surface geology:

Water may be necessary as a lubricant for plate tectonics. Whether or not this is the case, Venus does not have plate tectonics. It instead has a stagnant lid geology, punctured occasionally by extreme vulcanism (Siberian traps level vulcanism, and then some).

What are the observations that lead to this conclusion? The existence of plate tectonics on Earth was first determined by putting a lot of pieces of the first-hand observational puzzle together. There's much less data available from Venus.

Answer 1

There's much less data available from Venus.

Some data exists. As mentioned in HDE 226868's answer, maps of Venus's surface exist. Like Earth's atmosphere, Venus's atmosphere is transparent to some low frequency electromagnetic radiation such as those used by radar. These observations are consistent with a planet that has stagnant lid tectonics and inconsistent with a planet that has active plate tectonics; more on this below.

In addition to these remote observations, the Soviet Union successfully sent several spacecraft into Venus's atmosphere, some of which landed and briefly operated on the surface of Venus. The initial attempts failed because nobody thought the surface conditions on Venus would be as brutal as they are. To make landing successful, the Soviet Union had to significantly downsize the parachutes and they had to use materials and avionics that could withstand very high temperatures.

Every piece of evidence gathered to date regarding Venus is inconsistent with a planet with active plate tectonics:

• Venus surface temperature and pressure are well above water's critical point. Venus cannot have any liquid water on its surface. Water is widely (but not universally) thought to be critical as a lubricant that enables plate tectonics to occur.
• The radar observations show a planet with a nearly universal surface age, about half a billion years old. This is inconsistent with a planet with active plate tectonics but consistent with a planet with stagnant lid tectonics.
• Venus's atmosphere is very thick, much thicker than the Earth's atmosphere, and is dominated by carbon dioxide. Plate tectonics recycles carbon dioxide at subduction zones. Stagnant lid tectonics does not. A planet with plate tectonics will see a gradual reduction in the amount of carbon dioxide in its atmosphere over geologically long periods of time. A planet with intermittently active stagnant lid tectonics will instead see a gradual increase in the amount of carbon dioxide in its atmosphere over geologically long periods of time.
• Multiple physics-based models of a planet with very high surface temperatures suggest that such planets will have rather thin and rather ductile crusts that can readily repair themselves against damage caused by subsurface tensions.

Note very well: The stagnant lid tectonics of hot terrestrial planets such as Venus and possibly Titan (Titan is "hot" because its geology is ice-based rather than rock-based) is rather different from the stagnant lid tectonics of cold terrestrial planets such as the Moon and Mars. The surfaces of the Moon and Mars are very old. The surface of Venus is much younger in comparison. Venus has undergone at least one somewhat recent nearly global resurfacing event. This has not happened on the Moon or Mars. Plate tectonics appears to require a planet whose surface is neither too cold nor too hot, and that has a good amount of liquid water on the surface.

Some references:

• David Bercovici and Yanick Ricard, "Plate tectonics, damage and inheritance," Nature 508.7497 (2014): 513.
  DOI: 10.1038/nature13072.
• A. Davaille, S. E. Smrekar, and S. Tomlinson, "Experimental and observational evidence for plume-induced subduction on Venus," Nature Geoscience 10.5 (2017): 349.
  DOI: 10.1038/NGEO2928.
• James F. Kasting and David Catling, "Evolution of a habitable planet," Annual Review of Astronomy and Astrophysics 41.1 (2003): 429-463.
  DOI: 10.1146/annurev.astro.41.071601.170049.

• Mikhail A. Kreslavsky, Mikhail A. Ivanov, and James W. Head, "The resurfacing history of Venus: Constraints from buffered crater densities," Icarus 250 (2015): 438-450.
  DOI: 10.1016/j.icarus.2014.12.024

• Ignasi Ribas et al., "Evolution of the solar activity over time and effects on planetary atmospheres. I. High-energy irradiances (1-1700 Å)," The Astrophysical Journal 622.1 (2005): 680.
  DOI: 10.1017/S0074180900182427.
  Accessible pdf: https://iopscience.iop.org/article/10.1086/427977/pdf.

Answer 2

Essentially, it boils down to the question of uniformity.

Magellan reached Venus in the early 1990s, and was able to greatly improve on previous mapping attempts. The spacecraft was able to map essentially all of the surface, including the distribution of craters. By measuring the crater density, scientists found that the surface was fairly uniform; given our knowledge of cratering on other inner Solar System bodies (e.g. the Moon), they were able to say that the surface is roughly 500 million years old.

What's more, that's a uniform figure - while there are variations across the planet, it's believed that they're due to local resurfacing events from volcanism. One possible explanation for the planet's particular age is that it underwent a period of global volcanic activity about 500 million years ago, and the entire crust was essentially reformed.