Mars Geology and Comparative Planetary Science

Overview

Mars is a geological treasure trove. Despite being half the diameter of Earth, Mars hosts the solar system’s largest volcano (Olympus Mons, 21.9 km high) and longest canyon system (Valles Marineris, 4,000 km long). In this two-part lesson, students analyze real NASA topographic data to compare geological features on Earth and Mars, developing explanations for why these worlds evolved so differently.

Background for Teachers

Why Mars Has Extreme Geology

The key to understanding Mars geology is plate tectonics — or rather, the lack of it. Earth’s lithosphere is divided into moving plates, which distributes volcanic activity across the surface. Mars lacks plate tectonics, so volcanic hotspots remain stationary. Olympus Mons grew so large because the same hotspot kept building the same volcano for billions of years.

Key Geological Features

Olympus Mons:

• Shield volcano, 21.9 km high (2.5 times the height of Mt. Everest)
• 600 km in diameter (roughly the size of Arizona)
• Caldera complex at the summit is 80 km wide
• Formed by sustained volcanic activity at a fixed hotspot

Valles Marineris:

• Canyon system stretching 4,000 km (the distance from New York to Los Angeles)
• Up to 7 km deep (4 times deeper than the Grand Canyon)
• Formed primarily by tectonic rifting and collapse, not water erosion
• Some evidence of water-related erosion on the canyon walls

Tharsis Bulge:

• Massive volcanic plateau, 10 km above mean elevation
• Contains Olympus Mons and three other large shield volcanoes
• Formed from a deep mantle plume — similar to Hawaii’s hotspot but with no plate movement

Impact Craters:

• Hellas Basin: 2,300 km diameter, 7 km deep — one of the largest impact structures in the solar system
• Mars preserves ancient craters because it lacks plate tectonics, heavy erosion, and biological processes that destroy craters on Earth

Lesson Procedure

Day 1: Volcanic Features (45 minutes)

Opening Investigation (10 minutes)

Display the MOLA global elevation map of Mars (color-coded by altitude). Without labeling features, ask students:

1. “What patterns do you notice in the elevation data?”
2. “Where are the highest points? The lowest?”
3. “What geological processes might create these features?”

Olympus Mons vs. Mauna Kea (20 minutes)

Provide students with topographic profiles of both volcanoes drawn to the same scale.

Data comparison activity:

Guided questions:

1. Calculate the ratio of height to diameter for each volcano. What do the gentle slopes of Olympus Mons tell us about the type of lava?
2. Why is Olympus Mons so much taller than any volcano on Earth?
3. Graph both volcano profiles on the same axes. What differences stand out?

Key concept: Introduce plate tectonics as the explanation. On Earth, the Pacific Plate moves over the Hawaiian hotspot, creating a chain of islands. On Mars, no plate movement means the same spot keeps erupting and building one enormous volcano.

Modeling Hotspot Volcanism (15 minutes)

Simple demonstration: use a candle (hotspot) beneath a sheet of aluminum foil.

• Mars model: Hold foil stationary above candle — heat concentrates in one spot
• Earth model: Slowly slide foil over candle — heat marks appear in a line (like the Hawaiian island chain)

Students sketch both models and write an explanation connecting them to planetary geology.

Day 2: Canyons, Craters, and Planetary Evolution (45 minutes)

Valles Marineris Investigation (15 minutes)

Provide elevation profiles across Valles Marineris and the Grand Canyon at the same scale.

Discussion: “These two features look similar from far away, but they formed through completely different processes. What does this teach us about making assumptions in science?”

Impact Crater Analysis (15 minutes)

Display images of fresh and degraded impact craters on Mars alongside craters on Earth (Barringer Crater, Chicxulub).

Student activity: Examine a set of Mars crater images of varying ages and states of preservation. Rank them from youngest to oldest based on:

• Sharpness of rim
• Presence of ejecta blanket
• Smaller craters inside (younger craters overlap older ones)
• Evidence of erosion or infilling

Key concept: Mars preserves its geological history far better than Earth because it lacks plate tectonics, significant water erosion (in recent geologic time), and biological activity that would break down and recycle rock.

Synthesis: Why Did Earth and Mars Diverge? (15 minutes)

Class discussion and note-taking:

1. Both planets formed from the same solar nebula about 4.5 billion years ago
2. Both started with volcanic activity and likely had liquid water
3. Mars is smaller — it cooled faster, lost its magnetic field, and its atmosphere was stripped by solar wind
4. Without a thick atmosphere, water was lost to space or froze
5. Without plate tectonics, geological recycling stopped

Final reflection: Students write a paragraph explaining how Mars’s geological features serve as a record of planetary history that Earth has largely erased through active geology.

Assessment

• Data analysis worksheets: Accurate calculations and graph construction for volcano and canyon comparisons
• Crater ranking activity: Correct relative ordering with justification based on observable evidence
• Synthesis paragraph: Demonstrates understanding of why Earth and Mars evolved differently

NGSS Alignment

• MS-ESS1-4: Construct a scientific explanation based on evidence from rock strata for how the geologic time scale is used to organize Earth’s history
• MS-ESS2-1: Develop a model to describe the cycling of Earth’s materials and the flow of energy that drives this process
• MS-ESS2-2: Construct an explanation based on evidence for how geoscience processes have changed Earth’s surface at varying time and spatial scales
• MS-ESS2-3: Analyze and interpret data on the distribution of fossils and rocks, continental shapes, and seafloor structures to provide evidence of the past plate motions

Extensions

• Use NASA’s Mars Trek web tool (trek.nasa.gov/mars) to explore Mars topography interactively
• Research the evidence for whether Mars’s volcanoes could erupt again
• Compare Mars’s geological history to that of Venus — another planet that lost its water
• Investigate how future Mars settlers might use volcanic caves (lava tubes) as natural shelters
• Write a proposal for a geological sample-return mission: which Mars site would you choose and why?