I’ve covered this topic before and now there’s interesting research on the Earth’s 27 million year extinction cycle and its potential cause. The “nemesis” concept, that is, a dark companion to our sun that periodically (say every 27 million years) passes through the Oort cloud and sends comets our way or otherwise does a drive-by on the solar system, was considered in this research and fairly clearly discredited.
From the second link:
Today, Adrian Melott at the University of Kansas and Richard Bambach at the Smithsonian Institute in Washington DC re-examine the paleo-record to see if they can get a more accurate estimate of the orbit of Nemesis.
Their work throws up a surprise. They have brought together a massive set of extinction data from the last 500 million years, a period that is twice as long as anybody else has studied. And their analysis shows an excess of extinctions every 27 million years, with a confidence level of 99%.
That’s a clear, sharp signal over a huge length of time. At first glance, you’d think it clearly backs the idea that a distant dark object orbits the Sun every 27 million years.
But ironically, the accuracy and regularity of these events is actually evidence against Nemesis’ existence, say Melott and Bambuch.
That’s because Nemesis’ orbit would certainly have been influenced by the many close encounters we know the Sun has had with other starsin the last 500 million years.
And here’s the good news:
There is a smidgeon of good news. The last extinction event in this chain happened 11 million years ago so, in theory at least, we have plenty of time to work out where the next catastrophe is coming from.