Sent in by William who makes the point, mainstream have no problem with catastrophism nowadays – as long as it happened a very long time ago. See www.yahoo.com/entertainment/alien-world-might-hiding-inside-130200108.html … continent sized remnants of an alien world may have left behind the evidence of worlds in collision. In this bit of speculation, after the hypothetical collision with the earth of a planet sized cosmic body, that is presumed to have created the moon by gouging out a rather big hole, some bits of the alien space body may have become lodged in the innards of the earth, awaiting discovery. That might take the invention of a machine to tunnel into the centre of the earth. The point is that this episode of worlds in collision occurred in Earth's infancy but is regarded as a plausible possibility. However, the red top Sun newspaper is more succinct – it is those blobs in the Mantle that gave the scientists the idea – see www.thesun.co.uk/tech/14442599/blobs-rock-earth-surface-alien-planet/
At www.dailymail.co.uk/sciencetech/article-9415075/ … sent in by Gary. Earth's 'Great Oxidation Event' saw oxygen levels surge – 2.3 billion years ago.