We think of the stars as immensely old, and in comparison to the brief span of our transient lives, they are. But many of the brightest stars we see in the night sky are young, far younger than the Earth and younger than many of the common rocks in your backyard. In this arresting image by the Canadian astrophotographer Wesley Liikane, for example, you see the oldest rocks on Earth contrasted with some of the youngest stars in the night sky.
The foreground of Liikane’s moonlit nightscape shows rocky outcroppings of the Canadian Shield west of Lake Huron in southern Ontario. The Shield dates back nearly 4 billion years, and most of its exposed rock is 2.5 to 3 billion years old. At that time, the Earth’s early atmosphere, which consisted mostly of nitrogen and carbon dioxide, began to endure the planet-altering Great Oxidation when immense blooms of blue-green algae released oxygen into the atmosphere.
The Canadian Shield is now geologically quiet. Most of the activity you find in these rocks is the rumble of dynamite and heavy equipment of miners looking for minerals and precious metals. But this immense expanse of igneous rock was formed by aggressive volcanism in the early days of our planet. Volcanic activity resulted in mountains as high as 12,000 m (39,000 feet), far higher than any mountains today. A couple of billion years ago, much of what’s now northern and eastern Canada was more rugged than the Himalayas.
These towering volcanic peaks have all been sandpapered down to bleak, rocky plains by wind, rain, and innumerable ice ages over the past 3 billion years. So much of the Canadian Shield is just 300 m to 600 m above sea level. Despite their great age, these rocks are covered by only a thin layer of soil because they were polished clean by the mile-high glaciers that slowly thundered across North America during the last ice age.
By contrast, the bright stars in and around the constellation Orion in the above image are quite young. Many are part of the Gould Belt, an elliptical necklace of stars tilted at an angle to the plane of the Milky Way. The origin of the Gould Belt is unclear. It may have formed when a large cloud of extragalactic dust and gas slammed into our part of the galaxy about 50 million years ago.
Most of the biggest stars produced in the Gould Belt have already detonated as supernovae. This has triggered further star formation which proceeds apace, most vigorously in the famous Orion Nebula in the sword of the constellation Orion. Many stars in Orion are second-generation members of the Gould Belt. Rigel, Orion’s western “foot”, is just 8 million years old. The stars of Orion’s Belt are even younger. They formed about 5-6 million years ago, around the same time our ancestors Australopithecus were spreading across the African continent.
So they may not look like much compared to the bright blue-white stars of Orion, but the ancient rocks of Earth have been around a lot longer. Of course the distinction between stars and Earthly rocks doesn’t really matter if you take a cosmic view of things. Because before the Sun coalesced 5 billion years ago, the stuff of the Earth, rocks and all, was all “out there” floating among the stars.
(Note: Thanks to Wesley Liikane for his generous permission to use his image “Orion Over Killbear”. You can see more of Wesley’s nightscapes and nature photography at www.cowboywithacamera.zenfolio.com).