Meteor and asteroid impacts: doom-laden myths dispelled

Among the marvellous stories that decorate Incoming!, an excellent newly published history of meteorites, is one that describes the rapid rise and fall of Elagabalus, an eccentric teenage Roman emperor.

In a temple on the Palatine Hill, Elagabalus installed a heavenly object of veneration.The thunderstone, which had fallen into the Syrian Desert, was believed to be the embodiment of the god El-Gabal. Each summer solstice, a chariot carried the meteorite around, with Elagabalus walking backwards before it.

But meteorites were often associated with doom – and that turned out to be the case for Elagabalus, whose worship of the rock became yet another reason for him to be deposed, along with his marrying a succession of women, including a Vestal Virgin, his transsexuality, and his relationship with a blond chariot driver. In the end, Elagabalus was beheaded and his remains tossed in the Tiber, after the soldiers of the Praetorian Guard lost patience with the way that, as Edward Gibbon put it, the emperor had "abandoned himself to the grossest pleasures and ungoverned fury".

His demise paved the way for Alexander Severus, a safer pair of hands. And that is the message of Ted Nield's book: that meteorites are not all bad news, since these destructive leftovers of the birth of the solar system more than 4.5 billion years ago can make way for new blood.

The best known example is the impact in present-day Mexico, 65 million years ago, of a rock six miles wide, which shrouded the planet in darkness and triggered a global winter. Colossal eruptions of volcanoes created the Deccan traps in India, generating some of the longest lava flows ever seen, along with thousands of billions of tons of noxious gases. Species that couldn't adapt to this hell promptly became extinct.

But as Nield points out, while the asteroid spelt disaster for the dinosaurs, it was good news for mammals. As a recent study by Jessica Theodor and colleagues at the University of Calgary showed, with less competition for vegetation, mammals could evolve and get about a thousand times bigger.

And this is not the only example of how meteorites can create opportunities for life. There was also the Great Ordovician Biodiversity Event, around 470 million years ago. The likeliest cause of this surge in the numbers of species can be found in space: a widespread bombardment of the Earth as a large asteroid broke up to unleash a swarm of smaller rocks that battered the Earth for millions of years.

Fossil meteorites in mid-Ordovician rocks suggests that the rate of impacts was around 100 times what it is today. This would have caused sufficient mayhem – local extinction events – to free up space for new species to flourish. The seas, where the majority of life resided, were overrun by newfangled life forms. First came massive algal blooms. These nourished filter-feeders, kick-starting an evolutionary bonanza of sponges and corals, along with reefs that were hot spots of biodiversity. There was a rise in brachiopods – shelled creatures that look something like clams – as well as bushy bryozoans and flowery crinoids, or sea lilies. Wander along the shoreline and the chances are that many of the creatures you come across, including sea urchins and star fish, emerged in this era.

And, strangely enough, a similar effect paved the way for the success of gene transplants to treat disease. In the Nineties, there was much excitement about the potential of "gene therapy", but it took another decade to make it work.

Read more at The Telegraph