The Ordovician meteorite rain
When an asteroid broke apart and Earth was showered with meteorites for millions of years.
Key facts
- When
- beginning about 466 million years ago
- Where
- Worldwide; best recorded in southern Sweden
- What hit
- debris from a parent asteroid perhaps 100 to 200 km across, broken apart in the asteroid belt
- Era
- Deep time
- Location
- 58.55° N, 13.40° E
Not one blast but millions of years of extra meteorites and craters: Earth received perhaps a hundred times more meteorites than today.
Many of today's L chondrites, the second most common meteorites, come from this same break-up.
What happened
About 466 million years ago, two bodies collided in the asteroid belt and shattered the parent asteroid of the L chondrites. Debris spread out, and some of it found its way to Earth.
In limestone quarries at Kinnekulle in southern Sweden, workers and scientists have found more than a hundred fossil meteorites in a few metres of rock laid down on the sea floor during the Ordovician period. The meteorites themselves have been replaced by other minerals, but they still contain grains of the mineral chromite with the chemistry of L chondrites.
The rate of arrivals in these layers is around a hundred times higher than today, and it stayed high for millions of years. Several impact craters of about the same age are also known, including Lockne in Sweden.
Effects
Some researchers have proposed that fine dust from the break-up cooled Earth's climate and helped trigger an ice age, or that it influenced a great burst of new species in the oceans at that time. These links are interesting but still debated.
The evidence
The fossil meteorites and chromite grains in Swedish, Chinese and Russian limestones, and the many L chondrites that fall today which were heated and shocked about 470 million years ago, the time their gases were driven out.
Did you know?
The Kinnekulle fossil meteorites were first noticed by quarry workers cutting limestone slabs for building.
One fossil meteorite from the same rocks, Österplana 065, is unlike any known meteorite type: a piece of a different asteroid, now gone.
Related pages
How is impact energy measured? See energy explained, or try the impact calculator.