Notes
Wednesday, 16 September 2026 · PlanetaryFormation.com
Continental class
Mars’s mean crust sits with Earth’s continents, not with Earth’s global mix.
Mars
Mars is half Earth’s width. Its crust sits with Earth’s continents.
Earth’s continents are typically 35 to 40 kilometres thick. Ocean floor is 7 to 11. Mix land and sea by area and the global mean drops to about 22 kilometres. That mix exists. It is not the lid to compare.
Mars, planet-wide, sits near 42 to 56 kilometres. Southern highlands run 45 to 63. Northern lowlands are thinner, about 37. InSight, one station in the north, prefers about 39 ± 8. Those numbers sit with Earth’s continents, not with Earth’s ocean floor.
This site reads Io through Mars as consecutive stages of one kind of planet, with living Earth as the present chapter. Mars is the last window before living Earth. A shell already in the continental range is what that window can look like. The missions do not prove the handoff.
Figure 1. Mars topography from the Mars Orbiter Laser Altimeter. Higher southern highlands against lower northern plains. Image: NASA / MOLA.
The ordinary view
InSight and later surface-wave work put a global mean crust on Mars in the 42-to-56-kilometre band, consistent with gravity models in a wider 30-to-72-kilometre range. Earth compilations still put continents near 35 to 40 kilometres and ocean basins near 7 to 11. The often-quoted “twice as thick as Earth” line uses the 22-kilometre global mix. That mix exists. It is not the comparison.
What was measured
| Lid | Typical thickness |
|---|---|
| Earth, continents | 35–40 km |
| Mars, global average | 42–56 km |
| Mars, southern highlands | 45–63 km |
| Mars, northern lowlands | ~37 km |
| Mars, under InSight (north) | 39 ± 8 km |
| Earth, ocean basins | 7–11 km |
| Earth, land and ocean averaged | ~22 km |
| Earth | Mars | Mars / Earth | |
|---|---|---|---|
| Mean radius | 6,371 km | 3,390 km | 0.53 |
| Surface area | 510 million km² | 145 million km² | 0.28 |
| Volume | 1.08 trillion km³ | 0.16 trillion km³ | 0.15 |
| Crust as a share of radius | ~0.6% (continents) | ~1.5% (mean ~50 km) | — |
Table 2. Mars is half Earth’s width and about a seventh of Earth’s volume. Per kilometre of radius, Mars has more crust.
What would move a clock
| Row | What would move it | What would not |
|---|---|---|
| Continental-class thickness | A new global map that puts Mars near 10 km planet-wide | A few kilometres either way inside 42–56 km |
| Not the 22 km mix | Using Earth’s land-and-ocean average as the lid to compare | Quoting 22 km as a talking point, then setting it aside |
| Last-stage pairing | Mars crust shown to be ocean-floor class after all | InSight moving the north-station number inside the same band |
On this reading
This site reads Mars as the last window before living Earth: a stagnant lid, highlands against a lowland that once held water. If that order is useful, the last proto-world would already have a shell in the continental range. It would not have to begin as a 7-kilometre ocean floor.
A later, larger face would have more area under the same rock. That is geometry. It is not a law that the crust must flatten, and it is not a finding that Mars is expanding.
What would weaken this
A new global map that puts Mars near 10 kilometres planet-wide would drop it into the ocean-floor class and end the comparison. A few kilometres either way inside the present 42-to-56-kilometre band would not. InSight is one station. The band can move. Neither result would prove a handoff.
What this page holds
Mars is half Earth’s width. Its crust sits with Earth’s continents, not with Earth’s ocean floor. This site reads Mars as the last stage before living Earth. The thickness is the measurement. The missions do not prove the handoff.
Sources
Kim, D., and colleagues (2023). Surface waves orbiting Mars. Global mean crust 42–56 km.
Wieczorek, M. A., and colleagues (2022). Global thickness consistent with InSight: about 30–72 km.
Knapmeyer-Endrun, B., and colleagues (2021). InSight crust under the lander; preferred three-layer reading 39 ± 8 km.
Mooney, W. D., and later ECM1 compilations. Earth continents ~35–40 km; ocean basins ~7–11 km; area-weighted global mean ~22 km.