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Starts With A Bang

Why Earth is the only planet with plate tectonics

Mercury, Venus, and Mars are all uni-plate planets, and may always have been. Here’s what’s known about why Earth, uniquely, has plate tectonics.
mauritius reunion ISS earth night
This image, taken from the International Space Station by astronaut Karen Nyberg in 2013, shows the two largest islands on the southern part of the Mascarene Plateau: Réunion, in the foreground, and Mauritius, partially covered by clouds. These features can only arise on an ocean-covered world with plate tectonics, and evidence suggests that anything more than a single plate, despite the internal heat produced inside of Earth, may not be possible without the interplay of water as well.
Credit: NASA/Karen Nyberg
Key Takeaways
  • Here in our Solar System, of all the known planets, only Earth — not Mercury, not Venus, and not Mars — is known to possess plate tectonics.
  • Although Earth is relatively large for a rocky planet, as you can only be about twice as massive before you hang onto a volatile gas envelope, size and internal heat isn’t enough to guarantee plate tectonics.
  • But clues from Jupiter’s moons, which may exhibit their own version of ice-plate tectonics, might point to the ultimate reason why: perhaps water + size makes it possible.

Terrestrially, plate tectonics are a vital part of Earth’s evolution.

Earthquake map of the world
This map of Earth shows, in black, the more than 300,000 earthquake epicenters identified from 1964-present. The earthquake locations clearly trace out a number of “lines” on the map, which correspond to a number of boundaries between tectonic plates here on our planet.
Credit: A. El-Aziz Khairy Ebd el-aal, Egyptian National Seismological Network, 2011

The crust and upper mantle form the lithosphere: fragmented into a series of plates.

diagram of plate tectonics on Earth
At the boundary between two plates on Earth, they can either diverge, where new crust is produced as the plates pull apart, converge, where crust is destroyed as one plate is pushed beneath another, “transform” where they slide horizontally past one another, or at boundary zones where interactions are unclear. These are responsible for and related to surface features such as mountain-building, earthquakes, volcanoes, and more.
Credit: USGS

These plates collide, spread apart, uplift, and subduct, creating diverse surface features.

hawaii hotspot earth mantle plume
The Hawaiian islands, like most island arcs that form on Earth, initially arose as a mantle plume delivered material up to Earth’s surface by rising through the crust. Over time, the lava builds up to poke above Earth’s oceanic surface, and then, as the plate slides over so that the forming, growing mountain is no longer over the same hot-spot, a new island begins to form. Once a mountain has moved off of its hotspot, it can only erode, not grow any further. This provides strong evidence for Earth’s active lid tectonics; a property not presently seen on Venus.
Credit: Joel E. Robinson, USGS

From mountain formation to volcanic island chains to oceanic spreading, plate tectonics affect Earth globally.

Lake Baikal
Lake Baikal, as viewed from space aboard NASA’s OrbView-2 satellite. Lake Baikal is the 7th largest lake in the world by surface area, but holds more fresh water than any other lake by quite a wide margin. It is the deepest continental rift valley, formed when plates spread apart, known on Earth.
Credit: SEAWIFS Project, NASA/GSFC

Continental drift creates and breaks apart supercontinents many times throughout history.

supercontinent breakup
This animation shows the breakup of supercontinent Gondwanaland, which itself was a large subsection of Pangaea at one point, into the smaller continents of South America, Antarctica, Africa, Australia, as well as components of other continents that are recognizable, such as Arabia and India. The theory of plate tectonics and continental drift is so successful because of the evidence that supports it.
Credit: B. Goldberg/Quora, modified by E. Siegel

But is Earth unique? No other known planet possesses plate tectonics.

densest planet
This cutaway view of the four terrestrial planets (plus Earth’s moon) shows the relative sizes of the cores, mantles, and crusts of these five worlds. There are compelling similarities between Earth and Mars, as they both have crusts, mantles, and metal-rich cores. However, the much smaller size of Mars means that it both contained less heat overall initially, and that it loses its heat at a greater rate (by percentage) than Earth does.
Credit: NASA/JPL

Mars is a single-plate planet, enabling Olympus Mons to form.

olympus mons
This computer-generated view of Olympus Mons shows the volcano’s size, its caldera, and its long, sloping sides that make it the largest planetary volcano presently known. Because Mars lacks plate tectonics, the magma chamber beneath Olympus Mons, when it erupts, keeps on growing this one volcano over and over. It’s been the Solar System’s largest for billions of years, and continues to grow over geologic timescales.
Credit: Dreksler Astral/Lowell Observatory

With an unmoving uniplate and a hotspot beneath it, Olympus Mons is the largest planetary volcano.

Mars topographic map MOLA Olympus Mons
Mars Orbiter Laser Altimeter (MOLA) colorized topographic map of the western hemisphere of Mars, showing the Tharsis and Valles Marineris regions. The impact basin Argyre is at lower right, with the lowland Chryse Planitia to the right (east) of the Tharsis region. Olympus Mons, near the upper-left, is the largest and tallest of the four major tall planetary volcanoes shown here on Mars.
Credit: NASA/JPL-Caltech/Arizona State U./Mars Global Surveyor MOLA Team

Mercury lost most of its mantle early on, having cooled to form a solid, one-plate planet.

densest planet
When it comes to the large, non-gaseous worlds of the Solar System, Mercury has by far the largest metallic core relative to its size. However, it’s Earth that’s the densest of all these worlds, with no other major body comparing in density, owing to the added factor of gravitational compression. Unlike Venus, Earth, and Mars, Mercury has no separate crustal layer to speak of.
Credit: Bruce Murray/The Planetary Society

But Venus, almost the size and mass of Earth with comparable internal heat, appears single-plated today.

Venus Earth comparison
Earth, in visible light at right, and Venus, as seen in infrared at left, have nearly identical radii, with Venus being approximately ~90–95% the physical size of Earth. Despite producing similar amounts of internal heat, Earth exhibits plate tectonic activity while Venus only has one single, non-moving plate. Both worlds, however, are volcanically active.
Credit: NASA/Magellan

Although it’s still volcanically active, Venus’s surface deforms, but doesn’t flow.

Venus active volcanoes magellan
These two images of the same region of the surface of Venus, taken by the Magellan spacecraft in 1990 and 1992, show evidence of a changing landscape: consistent with a volcanic eruption resurfacing and adding material to part of the imaged landscape depicted here. The resurfacing, or covering-over of previous craters, is extremely strong evidence for such a phenomenon. Io, however, was the second world in the Solar System (after Earth) that humanity discovered to be volcanically active.
Credit: R.R. Herrick and S. Hensley, Science, 2023

Perhaps Earth owes its tectonic uniqueness to global oceans, with hints found elsewhere.

Europa surface subsurface ocean
This artist’s rendition shows observed surface features on Europa mapped onto the theoretical subsurface structure of Jupiter’s second Galilean satellite. Numerous features that show evidence for plate tectonics are visible on the surface, although they’re ice plates, not rock plates on Europa.
Credit: K.P. Hand et al., Europa Clipper/NASA, 2017

Europa, Jupiter’s ice-covered moon, exhibits evidence for ice-plate tectonics.

Europa plate tectonics
This conceptual illustration of the subduction process (where one plate is forced under another) shows how a cold, brittle, outer portion of Europa’s 20-30 kilometer-thick (roughly 10-20 mile) ice shell moved into the warmer shell interior and was ultimately subsumed. A low-relief subsumption band was created at the surface in the overriding plate, alongside which cryolavas may have erupted. The Europa Clipper mission aims to research this moon of Jupiter further.
Credit: NASA/Noah Kroese, I.NK

Subduction and subsurface liquid upwelling occur there, with similar activity possible on Pluto.

Liquid water may be the key.

pluto subsurface ocean New Horizons
The geological features and scientific data observed and taken by New Horizons indicate a subsurface ocean beneath Pluto’s surface, encircling the entire planet. There may be plate-like behavior as various regions of Pluto’s icy crust collide, and possibly uplift and subduct: something that it may have in common with many worlds with large surface and subsurface quantities of water.
Credit: J.T. Keane et al., Nature, 2016

Internal heat plus water’s lubricating effects, combined, likely enable Earth’s flowing, sliding plates.

cutaway earth surface layers
Although only 0.02% of Earth’s mass is in the form of water, that water is distributed not only in the oceans, in stores of continental freshwater, and in icecaps and glaciers, but in groundwater as well. According to a 2023 study, approximately 0.00016% of all of Earth’s water was rearranged, from groundwater to ocean water, from 1993-2010.
Credit: USGS

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