Scientists believe Earth is under attack from tiny cosmic missiles weighing tons and travelling at 900,000 mph.
They are only the size of a pollen grain but so dense they can rip through the planet and exit on the other side in seconds.
Scientists have concluded that two mysterious explosions in 1993 were caused by the missiles, known as 'strange-quark nuggets' or strangelets.
Their theoretical existence was posited 20 years ago but no scientists have been able to confirm their existence until now.
A team of researchers from the Southern Methodist University in Texas studied earthquake data for evidence of strangelets hitting Earth.
Strangelets were formed in the Big Bang. They are predicted to have many unusual properties, including a density about 10 trillion (10 million million) times greater than lead. Just a single pollen-sized fragment is believed to weigh several tons.
The team analysed more than a million earthquake records for signs of strangelets hitting Earth, reports The Sunday Telegraph. They looked for events producing two sharp signals - one as they entered Earth and the other as it left.
They found two such events, both in 1993. The first in October when seismometers recorded a violent event in Antarctica that packed a punch of several thousand tons of TNT. The disturbance then ripped through Earth exiting through the floor of the Indian Ocean 26 seconds later - implying a speed of 900,000mph.
The second event in November started in the Pacific Ocean travelling through Earth to appear in Antarctica 19 seconds later.
The small size of strangelets means the blast is only big enough to have a very localised effect and humans are unlikely to be harmed.