Diamonds are a solid form of the element carbon, where the atoms are arranged in a rigid, crystal structure known as a diamond cubic. This unique atomic arrangement gives the material its unmatched hardness, making it a witness to the Earth’s most ancient history. To understand how long diamonds have existed, it is necessary to consider multiple timelines: the billions of years of their creation, the millions of years of their journey, and the thousands of years of human interaction. The ultimate answer to the question of a diamond’s age is not a single number but a complex geological and historical narrative.
The Ancient Timeline: Diamond Formation in Earth’s Mantle
Diamonds form deep within the Earth’s mantle between 1 billion and 3.5 billion years ago. This formation period places them in the Archaean and Proterozoic Eons, making many diamonds significantly older than the continents they are found beneath. The carbon atoms must be subjected to extreme conditions, occurring at depths of 90 to 150 miles (150 to 240 kilometers) below the surface.
The necessary conditions for a diamond to crystallize include temperatures between 1,650°F and 2,370°F (900°C to 1,300°C) and immense pressure. This environment is found almost exclusively beneath the stable, ancient cores of continents, known as cratons. If the carbon were to rise too close to the surface before crystallization, the lower pressure would cause it to stabilize as graphite, the soft material found in pencils.
Scientists determine these immense ages not by dating the carbon itself, but by analyzing tiny mineral fragments trapped inside the diamond during its growth. These mineral inclusions often contain radioactive isotopes like rubidium, samarium, or uranium, which decay at a predictable rate. By measuring the ratios of these elements to their decay products, geologists can accurately date the diamond’s formation event.
Carbon Source Tracing
The source of the carbon used to create diamonds can also be traced using stable isotopes, Carbon-12 (C12) and Carbon-13 (C13). The ratio of these two isotopes provides a fingerprint that reveals whether the carbon originated from the Earth’s deep, primordial mantle or from “recycled” crustal material. Carbon that has been part of organic life near the surface tends to be enriched in the lighter C12 isotope. The presence of both types indicates that diamonds form through complex processes involving deep-earth carbon cycling.
Bringing Diamonds to the Surface: Volcanic Transport
A diamond’s journey to the surface often occurs hundreds of millions of years after its formation. These ancient gems are transported rapidly and violently through vertical structures known as kimberlite or lamproite pipes. These are rare types of volcanic conduits that originate deep in the mantle, sometimes as far down as 280 miles (450 kilometers).
The eruptions that create these pipes are driven by volatile components like carbon dioxide and water, which travel upward at high speed. This rapid ascent is a necessary mechanism because it prevents the diamonds from spending too much time in the warmer, lower-pressure upper mantle. If the ascent were slow, the diamonds would revert back to graphite.
The age of the kimberlite or lamproite pipe is the age of the eruption, which is typically much younger than the diamonds it carries. While the diamonds themselves may be over 3 billion years old, the host rocks that brought them up are often only tens to a few hundred million years old.
These volcanic structures are typically carrot-shaped and are the primary source for most of the world’s commercial diamonds today. Before the discovery of these primary source pipes in the mid-19th century, humans only found diamonds that had been eroded from these pipes and carried by rivers into alluvial deposits.
The Human Timeline: Discovery and Early Use
The human timeline for diamonds is comparatively short, beginning only a few thousand years ago. The earliest confirmed discovery and use of diamonds dates back to ancient India, where they were found in alluvial deposits along rivers. Historical accounts suggest diamonds were known in India as early as 3,000 to 6,000 years ago.
The first uses were not primarily for jewelry, but as objects of religious and cultural significance. Diamonds were treasured as talismans believed to ward off evil spirits or were used as religious icons to adorn statues. Ancient Indian texts also mention their practical use as engraving tools, capitalizing on the stone’s extreme hardness.
From India, diamonds eventually made their way to Western Europe through trade routes, becoming fashionable accessories for the elite by the 1400s. The global market remained dependent on Indian supplies until the 18th century when deposits were found in Brazil. The discovery of the vast kimberlite pipes in South Africa in the late 1800s then revolutionized the diamond trade, making the gems more widely available.