Earth’s tectonic plates won’t slide forever

In a few billion years they’ll grind to a halt

Slowly, slowly, Earth’s crust — what we think of as its surface — reshapes itself. This has been going on month after month, year after year. It started several billion years ago. It won’t continue forever, however. That’s the conclusion of a new study.

Earth’s surface rock (and the soil or sand above it) moves slowly atop shifting rocky slabs known astectonic plates. Some plates collide, putting pressure on the edges of a neighbor. Their thrusting movement can lead to an upheaval of those edges — and the formation of mountains. In other places, one plate may slowly slide beneath a neighbor. But a new study argues that these movements of the tectonic plates could be a passing phase in our planet’s history.

After using computers to model the flow of rock and heat flow throughout Earth’s lifetime, scientists now now conclude that plate tectonics is just one temporary stage of a planet’s life cycle.

The computer model showed that in Earth’s youth, its interior was too hot and runny to push around the giant chunks of crust. After the planet’s interior cooled for some 400 million years, tectonic plates began shifting and sinking. This process was stop-and-go for about 2 billion years. The computer model suggests that Earth now is almost halfway through its tectonic life cycle, says Craig O’Neill. He’s a planetary scientist at Macquarie University in Sydney, Australia. In another 5 billion years or so, as the planet chills, plate tectonics will grind to a halt.

O’Neill and his colleagues report their conclusion in a paper in the June Physics of the Earth and Planetary Interiors.

Tectonics on Earth and beyond

It took billions of years before full-blown, nonstop plate activity was busy remodeling Earth’s surface. That early delay hints that tectonics might one day kick start on what are now stagnant planets, says Julian Lowman, who was not involved in the research. Lowman works at the University of Toronto, Canada. There, he studies Earth’s tectonic activity. He now suspects that there is a chance “that plate tectonics could start up on Venus.”

However, he adds, that’s only if the conditions are just right.

The intense heat flowing through Earth’s interior drives the motions of tectonic plates.Simulating that heat flow requires a computer to make complex calculations. Previous attempts to do that were too simple. They also typically looked only at brief snapshots of Earth’s history. And that,O’Neill suspects, is why they likely missed how plate tectonics has been changing over time.

The new computer model predicted Earth’s tectonic motions. It started its analyses from  the time of the planet’s formation, some 4.5 billion years ago. Then the model looked ahead some 10 billion years. Even using a supercomputer and simplifying how they modeled the planet, these calculations took weeks.

The new timeline suggests that plate tectonics is just a midpoint between two stagnant states in Earth’s evolution. Planets that started off with a different starting temperature would likely enter or end their tectonic period at a different pace than Earth's, the researchers now conclude. Colder planets may exhibit plate tectonics throughout their history while hotter planets might go billions of years without it.

Plate tectonics regulates a planet’s climate. It does this by adding and removing carbon dioxide from the atmosphere. This climate control has helped maintain Earth’s ability to support life. But lacking plate action does not mean a planet cannot support life, O’Neill says. Life may have emerged on Earth roughly 4.1 billion years ago. Back then, full-blown plate tectonics was not yet fully underway, the new computer model finds. “Depending on when they are in their history,” O’Neill says, stagnant planets may be as likely to support life as are those with moving plates.

Power Words

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carbon dioxide (or CO2)   A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

climate  The weather conditions prevailing in an area in general or over a long period.

computer model   A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

crust   (in geology) Earth’s outermost surface, usually made from dense, solid rock.

evolution    (outside biology) A term to describe the changes that naturally occur in some system over time in response to changing conditions.

greenhouse gas    A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.

plate tectonics     The processes governing the movements of massive pieces that make up Earth’s outer layer, which is called the lithosphere. Those processes cause the rock masses to rise from inside Earth, travel along its surface, and sink back down.

simulate    To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb.

simulation    To model, often using a computer, some conditions, functions or appearance of a physical system. A computer program does this by using mathematical operations that can describe the system and how it might vary in response to various situations or over time.

stagnant      Not moving. The adjective is used to describe things that normally move or flow, such as now-stagnant air or a now-stagnant stream.

supercomputer   A powerful computer that is able to carry out complex calculations more quickly than ordinary personal computers because it is able to perform many operations at one time

tectonic plates    The gigantic slabs — somespanning thousands of kilometers (or miles) across — that make up Earth’s outer layer.