Cyclical oscillations in biodiversity an explanation ?

The grand precession of the earth and the solar system around the spiral of the milky way ,has been thought to have cause changes to the earth and the solar system as we pass through cosmic clouds in a 64 million journey through the disc of the galaxy and back.
A substantial amount of theory exists on this as a prime vector in the cause of global cooling.

This weeks new scientist has another paper on this subject and the possibilty of this as a vehicle for global extinction.

The solar system's up-and-down motion across our galaxy's disc periodically exposes it to higher doses of dangerous cosmic rays, new calculations suggest. The effect could explain a mysterious dip in the Earth's biodiversity every 62 million years.
The solar system moves through the Milky Way rather like a child on a merry-go-round. It completes a circuit of the galaxy once every 100 million years or so but as it goes it bobs up and down through the dense galactic disc.

Still other researchers have pointed out that the clouds could compress the solar wind, which shields the solar system from energetic cosmic rays from the galaxy. These cosmic rays - charged particles accelerated to high energies by supernova explosions - could then leak into the Earth's atmosphere. There they could spur the formation of clouds - cooling the planet - and destroy the ozone layer, killing off species by allowing harmful ultraviolet light to reach the Earth's surface.

If the flux of cosmic rays drops, fewer clouds will form and the planet will warm up. No one yet understands the mechanism, which was first described in the late 1990s. But what makes it controversial is that climate models used to predict the consequences of rising levels of greenhouse gases do not allow for the effect, and may be inaccurate.