D. Krentzel (2011), A Triassic archosaur. Flickr – CreativeCommons.
Let me set the scene. It’s a sunny day in Laurentia, present day North America, circa 65 million years ago (Ma). A gigantic yet graceful Triceratops casually munches away on a fern frond, unaware that life on Earth will soon be very different. Thousands of kilometers away, an asteroid 10 km in diameter impacts at the Yucatan peninsula in the Gulf of Mexico with over 100 million megatons of force, setting into action a dramatic series of events that will see the sun set on the reign of the dinosaurs.
NASA (2011), The Chicxulub Impact. Wikimedia Commons.
At least that’s the story we are probably all familiar with. Indeed, that is the generally accepted theory for the cause of the mass extinction that marked the boundary of the Cretaceous and Paleogene periods (K-Pg; previously known as the K-T boundary) and resulted in the extinction of some 75% of all species on the planet. However, the details of where the asteroid came from and what caused it to come barreling to Earth are still being debated. As a recent article in Nature reports, the answers might be found in the periodicity of our movement through space. Allow me to explain.
Just as the planets orbit the Sun, our Solar System is moving through one of the arms of our galaxy, the Milky Way. However, the movement of our Solar System through the galaxy is not as simple as you might think. Not only are we hurdling through space at 70,000 km/hr, but the Solar System is also oscillating vertically through the galactic plane – a densely packed disk that slices through the centre of the galaxy. In the latest paper on the subject, soon to be published in Physical Review Letters, Lisa Randall and Matthew Reece (2014) propose that this disk may be composed of dark matter and that our Solar System moves through the plane at regular 35 million-year intervals.
Movement through this dense layer of dark matter is thought to cause gravitational distortion in the Oort Cloud, which is a hypothesized sphere of millions of asteroids that lies about one light-year away and surrounds our entire Solar System. Specifically, it has been hypothesized that in the centre of the galactic plane gravitational pull from the dark matter ‘stretches’ the Oort Cloud and weakens the effects of the Sun’s gravity. As the Sun exits the plane, the cloud rebounds and, similar to an elastic band shooting a wad of paper, asteroids may be sent flying into the inner Solar System.
So, is this elusive dark matter really to blame for the dinosaur’s demise? Maybe, but as astrophysicist Adrian Merlott points out, “dark matter is a possible explanation, but it’s not clear that it’s explaining anything real.” While the Chicxulub Impact Event is believed to be proximately responsible for the mass extinction 65 Ma, scientists are still searching for an ultimate, astronomical cause.
D. Young (2011), Milky Way Galaxy. Flickr – CreativeCommons.
– Joseph Burant
