QUESTION:
What instruments could scientists use to see if there is plate
tectonics on Mars?

ANSWER from Mike Mellon on April 1, 1997:
To answer your question, we can ask what how scientists determine that 
there is plate tectonics on Earth. Some Examples: Large geologic 
structures, such as long mountain ranges and mid ocean ridges, which 
mark the boundaries of the plates at zones of subduction or speading.  
The age of rocks on the ocean floor show younger rocks nearer the mid-
ocean ridges. Old mountain ranges on one plate that stop at the coast, 
then continue on another continent. We connect broken land masses like 
this by also looking for similar chemical make up of the rocks.  

On Mars we can look for the same things. Using cameras to take pictures 
of Mars from orbit we can look for large geologic structures. We can 
also determine a great deal about the chemical makeup from orbit by 
looking at spectra in a variety of wavelengths to identify what 
minerals and elements make up the surface; we can then map these 
minerals and elements and look for disconnected landmasses. Determining 
the age of rocks would require obtaining samples from a wide variety of 
locations and returning those samples to a laboratory for analysis.  
In addition, a network of seismic stations would tell us if there are 
localized belts of marsquakes that mark plate boundaries.