Vol. 4 Num 237 Sat. January 24, 2004  

1.5 billion-year-old meteorite crater found

A crater from a meteorite that collided with earth some 1.5 billion years ago has been discovered in Finland by two amateur geologists, Finnish scientists said.

The discovery is nine kilometres in diameter, but the original crater must have been much larger, because only the floor is left, since the rest of the crater bowl has eroded away, said Lauri Pesonen, a professor of geophysics at Helsinki University who verified the find.

According to calculations, the crater must have been between 20 and 25 kilometres wide following the impact, he added.

Two local amateur scientists, Satu Hietala and Jarmo Moilanen, came across the crater last fall when they found shatter cones in stones in the area.

Shatter cones, which are typical feature found in stones in meteorite craters, are formed in the rock when the energy from the impact passes through it.

Since the surrounding rock formation is about 1.8 billion years old, Pesonen said the meteorite was likely to have collided with the earth later than that, probably around 1.5 billion years ago.

The crater, partly covered by a lake, is located some 175 kilometres north of Helsinki.

So far, 11 meteorite impacts have been found in Finland, and some 180 worldwide, Pesonen said Thursday.