Meteor Impacts and Ourselves

I am fascinated and enthralled by things that fall from space and the marks they leave behind.  It’s not just my love of space, it’s is something far more profound, it is in part what those things signify.

Go to a museum, one that has meteorites.  Often there will be at least one display of a metallic body that you can touch.  Lay your hands on it, press your palms against it, feel the soft curves, the slightly nubby surface, the coolness of the blackened metal.  You are touching the core of an extinct planet.  That should give you pause and send a small shiver up your spine.

On Earth there less than 200 known, confirmed, impact structures.  Just looking at the map it is clear that the distribution is skewed to areas where there are many people (North America & Europe), exposed bedrock (Canada & Scandinavia), or regions where weathering is slow (Australia & North Africa).

Confirmed impact structures on Earth from:

Every other rocky body in the solar system is liberally coated in the scars left by impacts.  The Earth bears the history of its impacts in a different way.  Weathering, plate tectonics, and the oceans have served to hide the marks of the numerous past impacts.  Except…

The global ocean, that covers 70% of the surface of the planet to a depth of 7 miles in some places, this, the single largest surface feature of the planet, is impact derived.  It is believed that ALL the water on the planet arrived by cometary impacts soon after the planet formed.  The Moon is another large impact structure, a relict left over from  the collision of the proto-Earth and another roughly Mars sized body.

The frequency of large impacts has, thankfully, fallen over time, but they still happen.  Some of you, I hope all of you, may remember the comet Shoemaker-Levy 9, the comet that crashed into Jupiter in 1994 after being torn apart by Jupiter’s immense gravitational field.  The fireballs in Jupiter’s atmosphere were larger than the entire Earth, and there were multiple fireballs.

Shoemaker-Levy 9 impact on Jupiter

The energy released by each of the Shoemaker-Levy impacts was on a par with the Chicxulub impact in the northern Yucatan 65 million years ago that is implicated in the demist of all terrestrial animals larger than a piece of carry-on luggage.

On Earth impacts are still frequent, but most are small and do not survive passage through the atmosphere.  Think shooting stars, grains of sand and dust traveling at orbital speeds, around 20km/second.  Several months ago, on the last day of February, I was treated to a something more dramatic than one of these little grains of dust.  A little after 10pm on the 28th I was driving under a clear sky and the snow covered landscape lit-up with a bright blue flash.  I later found out that the flash of light had been seen from New Jersey to Quebec.  This was just one of the many fireballs that flash in the sky each year, probably something small only a few meters in diameter, an explosion not more than a few kilotons.

In a few places the scars left on the ground from large impacts are still visible.  One of my favorite ones is in NE Canada.  Canada is an excellent place for finding impact structures as much of the Canadian Shield is ancient, exposed bedrock.

Manicoaguan impact crater turned into a reservoir

The Manicoaguan impact is about 215 million years old and approximately 60 miles across.  It has been dammed and the island in the middle is now one of the largest fresh-water islands in the world.  Big impacts like this are rare, but they leave dramatic remains behind.

Small impacts are surprisingly common, the frequency rapidly trailing off the larger the impact.  This is good news, but the picture is very incomplete as we have only been able to watch carefully for a short period of time.

Impact frequency Table from

We are struggling to understand how the universe fits together and have tremendous difficulty comprehending the scales and energy involved.  We are too used to thinking on our small scales, our bodies, our houses, maybe our planet, for a few our solar system or galaxy.  Our solar system is huge, our galaxy immense, yet in the lager context of our body of knowledge and what we can see even the Milky Way galaxy is barely a microscopic speck.

Look at the ocean, lay back and watch the trails left by falling meteors, look at the background of stars, go to a museum and touch the heart of a planet, if you live near an impact crater go visit.

We often say, “We are all connected,” and this is true, and that web of connection is far greater, wider, and deeper than most of us realize.

Photography as a tool

The foundation of science is observation.  Sometimes we need help making observations as the things we are interested in are small, far away, in motion, or complicated.  Not every observation can be made in the field or at real-time.

Fortunately, we live in a time where there are numerous tools to assist with observation.  One of my favorites is a camera. A good photograph can make the minute gigantic, the distant close, freeze time, and illuminate details otherwise unnoticeable.  Sometimes it takes some thinking creatively to capture and image, but the results can be worthwhile.

Nearly everyone is familiar with the incredible Hubble Space Telescope images of objects deep in space and far in our past (HST image gallery).  These images are extremely high resolution, taken using a wide variety of sophisticated techniques including multiple color bands, non-visible light, and dift-scanning, a way of tricking digital cameras into taking continuous images larger than their CCD receiving array.

Taken with an 1Phone 4 through a microscope eyepieceHubble style techniques are out of the range of most of us, but with a little creative thinking and a steady hand everyone can get some surprisingly good results with basic equipment.

In a soil ecology lab I was having trouble seeing some of the detail, and had to write a report on the nematode species I’d seen on the slide.  A photo was just the thing I needed, so I used the camera on my iPhone held over the compound microscope eyepiece to capture the image to the right (click image for a larger photo).

The same technique works well with a hand lens to capture shallow depth of field images of other small things, and with binoculars or a telescope to capture images at a distance.

I have a confession to make.  Despite being a naturalist and being reasonably knowledgeable about the natural world, when it comes to birds I am hopeless.  Those speedy little feathered dinosaurs flit hither and yon faster than I can see their detail.  They hide in shrubs or high atop trees and fly away when I come close.  Usually they are small and the identifying features are tiny, the diagnostic mark is often something like the color of an eye-ring or a barely seen flash of color on the nape of the neck.

The songs will tell you which bird is which, but not what they look like, and, in any event, I can never remember tunes.

I have turned to photography to recognize and identify birds.  I cannot get photos of many of them, miss shots of others, but I am slowly learning my birds.

Dark Eyed Junco

 Canada Warbler


Yellow-Rumped Warbler





To learn about the world we need to observe it, but it does not stop there.  We need to think about what we observe and question our observations.  Photographs offer a way of fixing our observations in time, allow us to revisit them, and invite reevaluation of them.