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The Sudbury impact
The Sudbury Basin in Ontario is the scar of an asteroid impact 1.85 billion years ago, today an oval depression some sixty kilometres long. The Sudbury structure is the second-largest confirmed impact structure on Earth and the best exposed, because later mountain-building tilted it on edge and laid open a cross-section through the entire melt sheet. It was long read as volcanic; shocked quartz and shatter cones settled the question in the 1960s. Nickel from here supplied a substantial share of world production through the twentieth century.
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