Canyon Diablo
The iron that made Meteor Crater in Arizona – and helped scientists measure the age of the Earth.
Key facts
- Type
- Iron, IAB (coarse octahedrite)
- Fell or found
- Found
- Year
- 1891 (first scientific description)
- Country
- United States (Arizona)
- Mass
- about 30 tonnes of fragments recovered
- Official name
- Canyon Diablo
In the desert of northern Arizona lies a bowl-shaped hole about 1.2 kilometres wide and around 170 metres deep. Today it is known as Meteor Crater, or Barringer Crater, and it is one of the best-preserved impact craters on Earth. The iron meteorite that made it is called Canyon Diablo, after a canyon a few kilometres to the west. Fragments of it are scattered across the surrounding plain, and they have played a starring role in some of the most important discoveries in Earth science.
A crater debated
Iron pieces had been found around the crater by the 19th century. In 1891 the mineralogist Albert Foote described specimens of the iron and was surprised to find that they contained tiny diamonds. That same year, the geologist Grove Karl Gilbert investigated the crater and concluded, wrongly, that it had probably been made by a volcanic steam explosion.
From 1903, the mining engineer Daniel Barringer argued that the crater had been formed by a meteorite impact. He spent many years drilling in the hope of finding a giant buried mass of valuable iron. He never found it, because it does not exist: most of the impacting body was vaporised, melted or scattered during the impact. The crater's impact origin was finally established beyond doubt in 1960, when Eugene Shoemaker and colleagues found coesite, a dense form of silica (the substance quartz is made of) created only at the immense pressures of impacts, in the rocks there.
What happened
About 50,000 years ago, an iron meteoroid estimated at roughly 50 metres across struck the plateau at high speed. In a fraction of a second, it blasted out the crater, overturned rock layers around the rim, and sprayed iron fragments and melted droplets across the landscape. In total, roughly 30 tonnes of meteorite fragments have been recovered, ranging from tiny pellets to masses weighing more than 500 kilograms. Around the crater, collectors in the past also found tiny metal spheres, condensed from melted and vaporised iron, and rusted, weathered iron lumps known as shale balls.
Canyon Diablo is an iron meteorite of the IAB group. It shows a coarse Widmanstätten pattern when etched, and it contains inclusions of graphite and of troilite, an iron sulphide mineral. Some fragments were shocked so severely that graphite was converted into diamond. In 1967 a new form of diamond with a hexagonal crystal structure was described in Canyon Diablo fragments and named lonsdaleite, after the crystallographer Kathleen Lonsdale.
Dating the Earth
Canyon Diablo's most famous contribution came from its troilite. Iron meteorites contain almost no uranium, so the lead in their troilite has stayed essentially unchanged since the Solar System formed. That makes it a perfect record of the 'primordial' lead present at the start. In 1956 the geochemist Clair Patterson compared the lead isotopes of meteorites, including Canyon Diablo troilite, with lead from Earth and calculated an age for the Earth of about 4.55 billion years. That figure has stood the test of time.
The troilite has also served as an international reference standard for measuring sulphur isotopes, used by laboratories around the world.
Visiting the crater
Meteor Crater is privately owned and is a popular visitor attraction with a museum on the rim. Collecting meteorites on the crater property is not allowed, and the land around it is privately owned or otherwise protected. Apollo astronauts trained there before travelling to the Moon, learning to recognise the rocks of an impact landscape.
Why it matters
Canyon Diablo links meteorites to craters, to new minerals and to the age of our planet. It helped to show that impacts are real geological processes, provided the material for one of the most important age measurements in science, and continues to teach visitors about the power of cosmic collisions.
Did you know?
Lead from troilite in Canyon Diablo helped Clair Patterson calculate the age of the Earth as about 4.55 billion years.
Lonsdaleite, a hexagonal form of diamond, was described from Canyon Diablo fragments in 1967.
Daniel Barringer spent years drilling for a giant buried iron mass that does not exist.
See more
Canyon Diablo in the catalogueBarringer Crater (Meteor Crater) crater