A group of researchers have identified two seismic events that they think provide the first evidence of a previously undetected form of matter passing through the Earth.

The so-called strange quark matter is so dense that a piece the size of a human cell would weigh a tonne.

The two events under study both took place in 1993.

Other scientists are tantalised, saying that while these seismic disturbances are unlikely to have been caused by strange quark matter, they do not as yet have alternative explanations.