The dangers that come from space

We think of outer space as distant and unreachable, but in fact events out in the cosmos may have helped and hindered the evolution of life on Earth

We are here by the skin of our teeth. Evolution could well have turned out differently, and the fact that it did not may well be down to freak, chance events.

Life on Earth has faced a string of accidents, weird situations and outright catastrophes, from sudden ice ages to collisions with asteroids - and it is how life responded to these contingencies that ultimately led to us.

If that is so, we can only understand the story of life by taking the broadest possible view.

Organisms are shaped by their environments, and those environments are shaped in turn by huge geological forces like volcanoes and ice sheets, and by the shifting climate.

But we should cast the net even wider.

What if these great forces were influenced by even greater forces from the wider Universe?

Might cosmic events in our Solar System and even our galaxy have also played roles? Do we literally have to thank our stars that we are here?

The most well-known example of an evolutionary shift caused by astronomical events is the hypothesis that the dinosaurs were driven to extinction by a gigantic meteorite impact 66 million years ago.

This was proposed in 1980 by physicist Luis Alvarez, his geologist son Walter, and their coworkers.

The researchers discovered that sedimentary rocks, laid down all over the world at the time of the extinction, contain large amounts of a rare element called iridium.

The team suggested that the iridium might have come from the dusty debris of a meteorite that smashed into the Earth.

Iridium is more abundant in asteroids, the most likely source of such a meteorite, than it is on Earth.

Quite how such an impact might have killed off the dinosaurs remains a matter of debate, but there are many possibilities.

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