Pockmarked Planet

“I had kicked against a hard, black stone, the size of a man’s fist, a sort of moulded rock of lava incredibly present on the surface of a bed of shells a thousand feet deep. A sheet spread beneath an apple tree can receive only apples; a sheet spread beneath the stars can receive only star-dust. Never had a stone fallen from the skies made known its origin so unmistakably.”

– Anointe de Saint Eupéry, “Wind, Sand and Stars”

For today I am going to step aside from my usual photographic theme and write about a subject that has recently captivated my interest.

At 10:38 in the morning of February 12th, 1947, a large fireball was seen in the sky over the Sikhote-Alin Mountains of Russia. Approaching at 31,000 miles per hour, the meteor broke apart in an explosion about 3.5 miles above the ground. The fragments spread out over an elliptical area about a half mile wide, many of them leaving craters, the largest of which was six metres deep and 26 metres wide. The biggest piece weighs just over 1,700 kilograms and is on display in Moscow. Other fragments weigh from 1,000 kg down to a few grams. What was originally destined to be a part of the earth’s continuing accretion process found its way into rock specialty stores around the world.

A piece of the Sikhote-Alin meteorite next to a Canadian dime

Several of those pieces ended up in a rock shop in Whistler, British Columbia, and for $119 CND, one small but weighty fragment from outer-space came home with me.

There is quite a market for meteorites. Pieces can be collected from sites such as the Sikhote-Alin impact, when there are witnesses to the event. Otherwise, desert environments are excellent places to find meteorites, as French pilot and author Antoine de Saint Exupéry found out when minor plane trouble left him on a truncated cone of rock in the Sahara until help arrived. “Excited by my adventure, I picked up one and then a second and a third, finding them at about the rate of one stone to the acre.” Nomadic people who roam those sandy blankets that catch star-dust find plenty of meteorites and bring them to markets in Morocco, where they are sold to buyers who in turn sell them to collectors and museums.

Meteorites are classified into four main groups: Irons, Stony Irons (pallasites and mesosiderites), Chondrites and Achondrites. The first is from the core of planets or planetoids that were destroyed by some kind of catastrophe early on in the history of the universe. Pallasites are from the zone between the core and the mantle. Chondrites and Achondrites are from the crust and were formed by similar geologic processes involving igneous rocks as we find on Earth. There are also Lunar and Martian meteorites, which were blown into space when meteors impacted with the surface of the moon or Mars. These pieces of the Lunar and Martian crust may drift about in space for aeons before being pulled into the earth’s gravity well and coming shooting through the atmosphere. In 1911 in Egypt, a dog had the inauspicious honour of being the only recorded living thing to be killed by a piece of Mars when a Martian meteorite fell from the sky and struck the ill-fated creature. The number of man-made objects and living things struck by meteorites is surprisingly large (note the site claims that there is dispute over whether or not the dog was actually killed by a meteorite).

The earth was originally formed as the solar system coalesced and larger bodies of solid matter drew in smaller bodies. With increasing mass, the larger bodies became planetoids and eventually the accretion process of each planet swept up most of the large-sized debris floating about. But the blackness of space is still full of rocks and dust, some of it from our own solar system, some of it from other systems. It is estimated that the earth accretes some 214 tons of matter from space every day. Those wish-granting shooting stars are small meteors burning up in the atmosphere. Sometimes a larger chunk of space rock breaks apart and leaves a trail of orange smoke. These are called fireballs. I have been fortunate enough to witness three fireballs, the most recent only a couple of months ago. I happened to look up at the sky as I was walking home at night and a falling star suddenly left a telltale trail of smoke before bursting apart into three pieces that burned up quickly. If a fireball occurs low enough in the atmosphere, a roar of thunder may be heard. These fireballs are likely to leave meteorites intact to strike the earth.

When we look at the Moon or Mars we almost immediately recognize the pitted surfaces, craters made by meteor impacts. Do we see the same on Earth? At first glance it doesn’t seem so. All the most massive craters left by huge bolides have long since been erased by the forces of plate tectonics, erosion, and weathering. But Earth has its share of impact craters – 176 identified craters according to the Earth Impact Database web site. Many of these craters are hardly distinguishable from aerial or satellite photographs because they’ve been filled by sediments and their rims worn down, and also because of vegetation growth and human development of the land (for the criteria to determine a meteor crater look here). One had best search desert or tundra environments in order to find meteor impact craters. With the help of the   web site and Google Earth, I was able to find a couple dozen of these craters.

The East and West Clearwater Craters in Canada

The most famous meteor crater is the Barringer Crater in Arizona. A bowl-shaped pit in the middle of the desert, aerial views of the crater give a lunar impression. Australia also has a couple of famous craters: the Wolf Creek Crater and Gosses Bluff. Looking at the globe, however, there is probably only one crater that can be discerned from the landscape: the Manicougan Crater in Quebec.

One of the world's best recognized meteor craters, the Manicougan Crater in Quebec, Canada

It is easily recognized as a circular lake with a round island in the middle. The island is formed by the rebound effect when a sizable meteor impacts with the earth. Perhaps the majority of large craters have raised ridges or islands in the middle. I vaguely recall hearing once that Prince Edward Island is the raised land in a meteor crater. Looking at a map it does appear that there is a semi-circular crater with P.E.I. curving in the middle. The iron-rich soil occurring in a place that is surrounded largely by granite could be explained as the product of an iron-rich meteor impact. But when I searched the Net for more information I found nothing.

Vagaries and suspicions aside, there are craters to be found all around the world. Northern Canada, the deserts of Africa, Australia, and northern Scandinavia have some of the best examples of meteor craters, most of which are between 450 million and only a couple of hundred thousand years old. I have taken the liberty of copying some of the images from Google Earth and put them on Flickr. I have added some of them here for you to see.

I find it very exciting to think of how our planet has grown at the expense of smaller cosmic debris and that we can still find evidence of this growth in the craters and meteorites that are found around the globe. Our planet is truly a product of the stars.

The Ouarkziz Crater in Algeria

The New Quebec Crater in Canada

Note: All satellite photos here were copied from GoogleEarth and cropped and colour adjusted slightly. The photos are not used with permission.

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