Mount Thawr: The Ancient Rock Beneath Mecca

Mount Thawr stands to the south of the Grand Mosque in Mecca and is recognised worldwide for its role in Islamic history. Official Saudi visitor information states that, during the migration to Medina, the Prophet Muhammad and his companion Abu Bakr sheltered in the Cave of Thawr for three nights.

The mountain also holds a much older narrative, recorded in minerals rather than written sources. Thomas Winslow Sisson, a research geologist at the U.S. Geological Survey, calls it a geological “archive”, though Mount Thawr requires direct laboratory dating before its precise age can be confirmed.

An ancient clue beneath Mecca

Official geological sources describe the rock at Mount Thawr as tonalite: a coarse-grained, light-grey rock composed chiefly of plagioclase, a widespread feldspar mineral, together with quartz and dark minerals known as biotite and amphibole.

This material is part of a group of granite-like rocks created when magma becomes trapped beneath Earth’s surface and cools slowly enough for visible crystals to develop.

A 2025 regional assessment of the Arabian Shield - the ancient rocky base underlying much of western Arabia - gives ages of roughly 824 million and 802 million years for magma-derived rocks in the Makkah arc.

The arc is an ancient zone of volcanic and subterranean igneous rocks surrounding Mecca, and these dates suggest that certain nearby formations could be more than 800 million years old.

However, these figures are regional indicators rather than a direct date of origin for Mount Thawr. Rocks dating to around 665 million years ago are also found elsewhere across the wider shield, but they are part of distinct units and cannot automatically be interpreted as a second phase in the formation of this mountain.

How tiny crystals reveal deep time

How can a crystal smaller than a grain of sand disclose an age far beyond human experience? Geologists frequently rely on zircon, a resilient mineral capable of retaining uranium within its crystal structure as molten rock solidifies.

Uranium transforms into lead at predictable rates, forming a natural timepiece. Measuring both elements within zircon allows researchers to estimate when magma cooled into solid rock, while two different uranium-decay routes offer an internal check on the result.

The outstanding requirement is straightforward to outline, even though the laboratory process is exacting. Researchers would need representative Mount Thawr samples, detailed records of their locations, and direct zircon dating before giving the mountain a precise crystallisation age.

Ancient rock, younger Mount Thawr

The age of a rock does not automatically match the age of the mountain visible today. Tonalite could have solidified deep underground more than 800 million years ago, whereas the present-day landscape of western Arabia emerged much later as the Red Sea rift opened and Arabia separated from Africa.

Significant stretching started approximately 29 million to 26 million years ago, with research placing major uplift and erosion along the rift margins during the several million years that followed.

By around 13 million years ago, new ocean floor was developing in parts of the Red Sea, although the timing differs along this extensive and complex plate boundary.

In practical terms, stretching and heating altered the crust’s thickness and buoyancy, contributing to the rise of western Arabia while erosion stripped away overlying rock.

This was not a single, simple upward movement. Instead, mineral cooling records indicate several episodes of uplift and erosion.

How the Cave of Thawr may have formed

Photographs reveal rounded boulders and wide fractures characteristic of strongly weathered subterranean igneous rock.

From a photograph-based assessment, the geologist suggested that weathering slowly softened sharp edges along fractures, while gravity moved large blocks downhill.

Eventually, one block may have become wedged over a space between larger rocks, forming the natural roof of the shelter.

This is a credible explanation, but photographs alone cannot confirm every stage; detailed field mapping would be necessary to examine it properly.

Three clocks inside one mountain

The first clock records crystallisation. Uranium-lead dating of zircon could establish when the original magma cooled, providing the strongest direct assessment of whether Mount Thawr’s rock formed during an event more than 800 million years ago.

A second clock traces cooling as the rock travelled towards the surface. Techniques based on microscopic damage tracks in apatite, or helium held within minerals, can help reconstruct when deeply buried rock rose, cooled, and lost the material that formerly covered it.

The surface clock follows afterwards. Cosmic rays start to create rare isotopes in the outer few centimetres of exposed rock, and measuring these can show how long a boulder or cliff face has been exposed to the sky - a process sometimes likened to a geological “sunburn”.

Why direct testing matters

Mount Thawr may retain three linked chapters of Earth’s past: magma crystallisation, mountain uplift, and eventual exposure at the surface.

Direct sampling could transform a convincing regional interpretation into a timeline specific to the site, while field investigations could evaluate the proposed formation of the cave with full respect for its religious significance.

For the moment, the most accurate finding is both compelling and cautious. The mountain may contain rock that is more than 800 million years old, but its exact age is still an unresolved measurement rather than an established fact.

The principal regional geological assessment, led by Wadee Kashghari, was published by the Saudi Geological Survey as Critical Review of the Stratigraphy Framework of the Arabian Shield.