Iridium anomalies and fractionated siderophile element patterns in impact ejecta, Brockman Iron Formation, Hamersley Basin, Western Australia: evidence for a major asteroid impact in simatic crustal regions of the early Proterozoic earth In 2007 Richard Firestone and other American scientists presented a new hypothesis: that the cause was a cosmic impact like an asteroid or comet. The impact could have injected a lot of dust into First, we must be clear on what we mean by “mass extinction”. Extinctions are a normal part of evolution: they occur naturally and periodically over time. 1 There’s a natural background rate to the timing and frequency of extinctions: 10% of species are lost every million years, 30% every 10 million years, and 65% every 100 million years. 2 It would be wrong to assume that species going ug1Ri. The work, published Dec. 1, 2021, in Journal of the Geological Society, focuses on explaining why some meteorite impacts cause mass extinctions, while others don’t. For example, the famous But life on Earth has been drastically altered by asteroid impacts before; the Chicxulub crater, for example, is evidence of the planet-shaking strike that led to the extinction of the non-avian

major asteroid impacts on earth