The plates do not move fast: a few centimetres a year. But they never stop.
The question
A few centimetres a year: enough to open an ocean?
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What you do Choose a speed, then let time pass: a year, a lifetime, a million years, a hundred million. Watch the distance travelled.
Without JavaScript, here are the animation’s data.
| Where | Speed | Source |
|---|---|---|
| Mid-Atlantic Ridge (average) | 2.5 cm a year | 1 |
| Pacific Plate against North American Plate (average) | 5 cm a year | 2 |
| The fastest | more than 15 cm a year | 3 |
| Time span | Speed | Distance |
|---|---|---|
| 80 years (a lifetime) | 5 cm a year | 4 m |
| 1 million years | 2.5 cm a year | 25 km |
The distances are calculated: speed multiplied by time, as if the plate always kept the same speed. The drawing of the plates is not to scale.
The takeaway A few centimetres a year is invisible over a lifetime. Over millions of years, it is enough to open an ocean.
Photo credits 3
- The relief of the South Atlantic floor, between South America and Africa (NOAA). NOAA, Public domain, source
- The breakup of Pangaea: the continents, at first joined, move apart to their present positions (United States Geological Survey, ’This Dynamic Earth’). Jacquelyne Kious and Robert I. Tilling (USGS), Public domain, source
- Blue Marble: Next Generation, with land topography and sea-floor bathymetry, in equirectangular projection: map produced by Reto Stöckli, NASA Earth Observatory (NASA Goddard Space Flight Center). Reto Stöckli, NASA Earth Observatory, modified by NordNordWest, Public domain, source
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Sources 4
United States Geological Survey, This Dynamic Earth: The Story of Plate Tectonics, “Understanding plate motions” page (https://pubs.usgs.gov/gip/dynamic/understanding.html).
The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr), or 25 km in a million years.
Open access open the source · checked on 24 October 2026
United States Geological Survey, This Dynamic Earth: The Story of Plate Tectonics, “Understanding plate motions” page, passage on the San Andreas Fault (https://pubs.usgs.gov/gip/dynamic/understanding.html).
Along it, the Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr.
Open access open the source · checked on 24 October 2026
United States Geological Survey, This Dynamic Earth: The Story of Plate Tectonics, “Historical perspective” page, 1st paragraph (https://pubs.usgs.gov/gip/dynamic/historical.html) […] “Understanding plate motions” page, part on divergent boundaries (https://pubs.usgs.gov/gip/dynamic/understanding.html).
The theory of plate tectonics states that the Earth's outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one another as they ride atop hotter, more mobile material. […] The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr), or 25 km in a million years. […] The Arctic Ridge has the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr).
Open access open the source · checked on 24 October 2026
United States Geological Survey, This Dynamic Earth: The Story of Plate Tectonics, “Understanding plate motions” page (https://pubs.usgs.gov/gip/dynamic/understanding.html), paragraphs on the types of boundary.
Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. […] Such destruction (recycling) of crust takes place along convergent boundaries where plates are moving toward each other, and sometimes one plate sinks (is subducted) under another. […] The zone between two plates sliding horizontally past one another is called a transform-fault boundary, or simply a transform boundary.
Open access open the source · checked on 24 October 2026