The Earth's earliest tectonic activity: when the plates first separated and began to move.

The history of Earth spans over 4.5 billion years, during which the appearance of our planet has changed multiple times. This is one of the many unique characteristics of Earth: unlike any other known planet in the universe, Earth's surface is made up of rigid plates that are in constant motion, as noted by Live Science.

But when did the first tectonic plates appear, and how did they start to move? This is an extremely important question, as plate tectonics likely fuels the evolution and complexity of life on Earth. For centuries, people have sought answers to these questions, yet geologists still lack a definitive answer regarding the onset of tectonics: estimates range from 700 million to 4 billion years ago, when Earth was essentially still a "baby."

According to Robert Stern, a geologist at the University of Texas at Dallas, the oldest unequivocal evidence of modern plate tectonics dates back to the Neoproterozoic era—between 1 billion and 541 million years ago. It is during this period that the geological record of the planet reveals a wealth of ophiolites and blueschists—metamorphic rocks formed in subduction zones or areas where plates collide and sink into the Earth's interior.

Subduction is a hallmark of plate tectonics, so these widely distributed rocks convincingly indicate that plates interlocked and slid beneath one another. However, many researchers do not share Stern's viewpoint and consider it overly conservative.

This group of scientists agrees that rocks indicating plate tectonics first became widespread 700-900 million years ago, but they could very well have existed earlier and were simply erased over time.

According to Mark Harrison, an emeritus professor of geophysics at the University of California, Los Angeles, the Indian subcontinent collided with southern Asia only 55 million years ago, and much of this rock has already eroded. Moreover, the collision between Tibet and India is essentially still ongoing. If such recent evidence is disappearing, what hope do we have of finding something older?

Another group of scientists believes that plate tectonics likely began much earlier. There are numerous signs of some geological shift during the Archean eon—between 4 and 2.5 billion years ago. For instance, at least one ophiolite that remains today is dated at 2.5 billion years.

But that’s not all. In 2012, researchers discovered that more of the crust began to be recycled around 3 billion years ago. According to the study's authors, this may indicate a transition to subduction.

At the same time, a 2023 study examined zircon to investigate the Earth's magnetic field conditions during mineral formation. The results suggest that the grains have remained more or less stable since their creation around 3.4 billion years ago. This hints that landmasses did not move until that time.

However, scientists cannot rule out the possibility that different aspects of plate tectonics emerged at different times. Subduction may have started 3.8 billion years ago, but it took time for continents to begin drifting across the globe. Unfortunately, all the theories presented so far have their strengths and weaknesses.