This tin is a long way from home. It was lost off Israel over three thousand years ago. It most likely came from Cornwall, about twenty-four hundred miles away. A trace of lead inside it points to ore about two hundred and ninety million years old.
More than three thousand years ago, blades and tools around the Mediterranean were made of bronze. Bronze is about nine parts copper to one part tin. But tin is scarce. In the Earth's crust, copper is more than thirty times as common. And near where this tin was found, there were almost no big tin deposits. So where did it come from?
This is the seabed off the Carmel coast of Israel. Tin has come up here from three spots. At one, it lay with copper ingots and stone anchors. No hull has been reported. The team that excavated one site thinks a ship probably ran aground there in a storm. In two thousand and thirteen, they wrote that the tin's source could not yet be known.
But the tin kept a clue. It is smelted from a mineral called cassiterite, the tin ore. That ore takes in some uranium as it grows, but almost no lead. Over millions of years, the uranium slowly turns into lead. Smelting leaves the makeup of that lead unchanged.
In two thousand and nineteen, scientists measured that lead in tin from all three spots. On a chart, the ingots fall on one line. The longer the uranium has been at work, the steeper the line. Its slope gives a rough model age for the tin ore. It is about two hundred and ninety million years, give or take seventeen million. That assumes all this tin came from ore of one age and one source.
So the age rules places out. Tin ore in Afghanistan is only about eighty million years old. Egypt's is more than five hundred million years old. Turkey's is the wrong age too. That turns the search toward Europe.
But the age alone cannot pick one place. Tin ore formed around then in Spain, in France, in Germany, and in Cornwall and Devon. From the trace of lead alone, the team wrote, any of them could have supplied this tin. Some researchers argue that smelting often mixed extra lead into Bronze Age tin, so the method itself is still debated. So what else is in the metal?
One clue is indium, a rare metal found in some tin ore. Tin ore from Spain and France has very little. Cornish tin ore is often rich in it. So is the tin off Israel. The mix of tin atoms in it fits Cornish ore, though other regions overlap. And it is chemically much like tin ingots found off Devon, made from British ore. Put together, the team concluded that Cornish tin mines were the most likely suppliers. Other places could not be ruled out completely.
Cornwall is at the far end of Europe from that seabed. In a straight line, it is about twenty-four hundred miles. Nobody knows the route. The tin may have passed from hand to hand.
So what happened under Cornwall and Devon? After a long collision of continents, the crust there stretched thin, and rock deep below began to melt. From about two hundred and ninety-five million years ago, that melt rose and cooled into speckled granite. Body after body went in, until about two hundred and seventy-five million years ago. Today it stands up as moors and tors.
As the granite set, hot fluids from the magma carried tin into cracks. There it grew as cassiterite, in veins that miners call lodes. Under one mine, South Crofty, the lodes were already forming by about two hundred and eighty-six million years ago. That is the date on our calendar.
Over time, rain and rivers wore the veins down and washed tin ore into the valleys. In the Carnon Valley, an antler pick and a wooden shovel from tin gravels are over three thousand years old. By the Bronze Age, people were washing tin out of Cornish streams.
Much later, miners chased the veins under the sea. At Botallack, one shaft ran more than two thousand feet out under the sea.
Now go back to the seabed off Israel. A trace of lead in that lost tin points to ore about two hundred and ninety million years old. Under South Crofty, veins were forming by about two hundred and eighty-six million. The age from the lead is rough, and it cannot date a vein. But it fits the time Cornwall's tin veins formed.
That tin was lost a long way from home. And the trace of lead inside it still keeps a rough record of its ore's age.
