© Andrzej Wojcicki/CorbisAn artist’s illustration of an asteroid impacting Earth.
If you enjoy leaves turning, pumpkin patches and other rites of autumn, thank the giant impact event early in Earth's history which knocked our planet's axis off kilter, creating the seasons that we know and love today. But was there just one planet-tilting impact?
University of Western Ontario geologist Grant Young thinks there were two, separated by billions of years. He has been studying rocks from the Ediacaran Period, 540 to 635 million years ago and says he sees signs of massive changes to Earth's seasons and climate that can best be explained by a axis-shifting collision of a small planetary body into the ocean about 570 million years ago.
That's long after the famous smash up with a Mars-sized body that is credited with creating the Moon around 4 billion years ago and giving Earth its mild tilt and modern seasons. It was also at the time Earth was seeing the earliest animals, or metazoans, come into being.
"I think this might have stimulated the evolution of metazoans," Young told Discovery News.
The scenario he has presented in the October issue of
GSA Today is that there was first the collision that created the Moon. But instead of that giving Earth its current tilt (which wobbles a bit, and is currently at 23.5 degrees), that first event knocked the planet over almost on its side. That orientation would give the poles a temperate climate without nights for half the year and the equator much less sunshine all year round.
Comment: For some food for thought see: On viral 'junk' DNA, a DNA-enhancing Ketogenic diet, and cometary kicks