Mars for Earthlings > Lesson Modules > In-Class Activity 2- Is it a Soil?

Is it a Soil?

In-Class Activity 2_Weathering and Soils

Julia Kahmann-Robinson PhD and Marjorie Chan PhD, University of Utah Department of Geology & Geophysics


Identify Earth soil horizons and extrapolate what characteristics of soil would be observable on Mars.


Study Figure 1 (or the image provided by your instructor).

  1. What part of this picture is a soil and why?
  2. What criterion are students using to define a soil?
  3. Brainstorm at least four factors that create and form soil on Earth.
    • Factor 1:
    • Factor 2:
    • Factor 3:
    • Factor 4:
  4. Are all factors of equal influence? Explain why/why not.
  5. After discussing the soil forming factors, determine which factors exist and/or have the greatest influence on Mars. List and describe them.


Identifying Soil Horizons

In Figure 2 draw lines and/or labels at horizon boundaries. Indicate if any layers are not present.

O Horizon- thick organic-rich layer

A Horizon- relatively thin organic layer with rooting

E Horizon- leached layer (not always present)

B Horizon- mineral layer

C Horizon- Parent material

1. What characteristics of this profile might you observe on Mars? Can you observe it remotely? What do you think makes that yellow layer "yellow"?


  • The 5 soil-forming factors are: (1) parent materials (2) time (3) biota (4) topography and (5) climate
  • In order for a soil to be classified as a soil it must have evidence of life and/or plant material
  • With regard to general soil horizons: the O-horizon must have a thick layer of organic matter, an A-horizon typically has an abundance of roots and some organic matter, an E-horizon is a leached horizon (of most base-forming cations), the B-horizon is a mineral layer where minerals accumulate, the C-horizon has some characteristics of pedogenesis but still may show structures of the parent material such as bedding, the R-horizon is the parent material.


Observe Figure 3 from Mars at Mawrth Vallis, one of the landing site considerations of MSL Curiosity (captured via JMARS):

  1. What observations can you make of this image?
  2. What do you think the changes in color represent?
  3. Do changes in color follow any other pattern you can discern?


  1. If you had the opportunity to test the surface of Mars at Mawrth Vallis, what evidence would you look for to identify if soils are present.
  2. If soils were (are) present at Mawrth Vallis, what horizons would be most likely preserved?