Scientists have uncovered the oldest direct evidence that Earth’s tectonic plates were already moving about 3.5 billion years ago. The discovery challenges earlier ideas that the planet’s outer surface may have remained rigid for a long time after Earth formed.

Researchers from Harvard University analyzed magnetic signals preserved in extremely old rocks. Their findings suggest that parts of Earth’s crust were already drifting and rotating billions of years ago.

Tectonic plates shape many of the planet’s key geological features. Their movement forms continents, creates mountains, and influences long-term climate conditions. Scientists have long debated when this dynamic system first began.

The new study, published in the journal Science, provides the clearest evidence yet that early plate motion occurred much earlier than some theories predicted.

Researchers say the results show Earth’s crust was already divided into moving sections billions of years ago.

🪨 Ancient Rocks Reveal Early Earth Activity

The research focused on some of the oldest well-preserved rocks on Earth, located in the Pilbara Craton in Western Australia. These rocks formed during the Archean Eon, when early microbial life existed on the young planet.

Scientists examined more than 900 rock samples from over 100 locations in the region. The team drilled cylindrical cores from the rocks and analyzed their magnetic properties in the laboratory.

Tiny magnetic signals locked inside mineral grains act like a record of Earth’s ancient magnetic field. By studying these signals, researchers can determine where rocks formed and how the crust moved over time.

The process required highly sensitive instruments capable of detecting extremely weak magnetic signals. Researchers also heated samples to separate different magnetic signatures recorded throughout the rocks’ history.

Consequently, the analysis provided detailed clues about the movement of Earth’s early crust.

📊 Evidence Shows Large-Scale Crust Movement

The scientists discovered that part of the Pilbara region shifted significantly in latitude during a period about 3.5 billion years ago. The area moved from about 53 degrees to 77 degrees latitude over tens of millions of years.

The rocks also revealed that the region rotated more than 90 degrees clockwise. The movement likely occurred at speeds of several centimeters per year, similar to modern tectonic plate motion.

To confirm the findings, researchers compared their results with rocks from the Barberton Greenstone Belt in South Africa. Earlier studies showed that this region remained close to the equator during the same period.

These differences suggest that Earth’s surface was already divided into separate pieces of crust that could move independently.

🔬 Findings Change Understanding of Early Earth

Scientists have proposed several theories about how Earth’s early surface behaved. Some models suggested the planet once had a “stagnant lid,” meaning a single solid outer shell without moving plates.

The new evidence challenges that idea. The research shows that the lithosphere was already segmented into pieces capable of moving relative to one another.

However, researchers say the findings do not yet reveal exactly how the earliest tectonic system worked. Early plate motion may have been slower or more irregular than today’s tectonic activity.

🧭 Oldest Magnetic Reversal Also Detected

The study also identified the oldest known geomagnetic reversal, a process in which Earth’s magnetic field flips direction. During such events, a compass would point south instead of north.

These reversals occur because molten iron inside Earth’s core generates the planet’s magnetic field through a process known as the geodynamo.

Researchers believe reversals occurred less frequently billions of years ago than they do today. Understanding these early magnetic patterns may help scientists learn more about how Earth’s interior evolved.