Science Spin March 2009

Space rocks that fell to Earth - on Ireland

By Tom Kennedy

More than 20,000 meteorites of over 100 grams fall onto the Earth every year, and fortunately for us bigger hits, like those that created the 62 km long Sudbury Basin in Canada are rare.

Eight meteorites have been observed falling on Ireland since 1779, the largest being a substantial 27 kg rock that came down into Brisha townland, Co Limerick, on 10th December 1813, and the latest landed at Leighlinbridge, Co Carlow in 1999.

Always looked on with a certain amount of awe, these rocks from space are currently on view at the National Museum, Turlough, Co Mayo. Given the size, and speed of descent, it is amazing that no one, that we know of, has been killed by one of these rocks. Although some have crashed through roofs, the only known fatality was a dog, killed at Nakhla in Egypt by a meteorite from Mars.

Observers note that the descent of a meteorite is far from silent, and there is a great first hand account from 1865 that describes what happened in the parish of Clononlty, Co Tipperary.

"I, John Johnson, of the parish of Clonoulty, near Cashel, County Tipperary, was walking across my potato garden, at the back of my house, in company with Michael Fahy and William Furlong, on the 12th August, 1865, at seven p.m., when I heard a clap like a shot of a cannon, very quick, and not like thunder; this was followed by a buzzing noise, which was continued for about a quarter of an hour, when it came over our heads; and on looking up, we saw an object falling down in a slanting direction. We were frightened at its speed, which was so great that we could scarcely notice it; but after it fell, we proceeded to look for it, and found it at a distance of forty yards, half buried in the ground, where it had struck the top of a potato drill. We were some time on looking for it (a longer time than that during which we had heard the noise). On taking up the stone, we found it warm, milk warm, but not hot enough to be inconvenient. The next day it was given to Lord Hawarden."

That particular meteorite was later given to the TCD Geology Museum, but in another case, the meteorite of 1902 had hardly fallen when the British Museum rushed in to buy it. That action, among others like it, caused quite a stir, and was one of the turning points for Irish independence.

Irish meteorites are not the only rocks from space on show and among the smaller objects are the vitrified splashes from a massive impact 14,500,000 years ago. These green glass tektites were tossed over to the present day Czech Republic from the 24-km-wide Ries crater in Germany. In scale, this was relatively small compared to another impact that left a trail of strewn tektites stretching all the way from east Africa, Australia, to west China. In spite of its size, the impact site itself has never been identified, for unlike the pock-marked Moon, the Earth's surface seldom remains the same for long.

The second largest impact crater is the Sudbury Basin in Ontario, which is believed to have been caused by a 10 km wide monster hitting the Earth 1,850,000,000 years ago. That impact must have caused a lot of damage, but it left us with a miner's paradise, rich in nickel, copper, platinum, palladium and gold.