Tag: impact crater

Peering down onto an ancient Australian impact

By Phil Plait | January 11, 2012 7:00 am

When the first episode of Bad Universe aired, my Aussie friends complained about us choosing Sydney as the impact site of a small asteroid. We chose it because most other major cities have already been wiped out in TVs and movies, and the Sydney Opera House was so iconic we knew it would make a great visual (it did).

But as much as my friends complained, they had it easy. Check out this impact site just a few thousand kilometers west of Sydney:

[Click to impactenate.]

That’s Shoemaker (formerly Teague) Crater, an old impact crater about 30 km (19 miles) or so across. It’s a bit tough to see, but it’s the oddly wobbly circular shape right in the middle of this photo. Craters this big are hard to see from the ground, and are easier to identify from space; this shot was taken by an astronaut on the International Space Station. Like many large craters, it has multiple rings around it, probably formed as massive shock waves from the gigantic impact slammed through the ground. There’s a ridge at the bottom of the high-res photo that’s part of a heavily eroded outer ring. This crater is in the Outback, with mostly brown rock punctuated by colorful salty lakes.

I knew it was old just by glancing at it. Young craters look young: fresh, sharp rims, obvious outlines, sometimes surrounded by rays (long, straight features pointing away from the center of the crater, formed when plumes of ejected material collapse). This one is sloppy, vague, faded. Estimates of its age vary. It may be as young as 570 million years, or as old as 1.3 billion years! Some estimates put it even farther back along Earth’s timeline. Australia itself is ancient, with some parts having been around for 4 billion years. This crater dates back to the Precambrian age, when the most sophisticated lifeforms on Earth were soft multi-cellular microscopic creatures; the first true fossils of hard-shelled life were still millions of years in the future, even for the younger age range of the crater.

It’s hard to imagine that our lush green and blue Earth was once covered with craters like this. Heck, a few billion years ago this one would’ve been considered small! But two things have changed that: for one, the solar system had a lot more rocks to toss at us back then. Things have thinned out considerably in the past few billion years. Plus, the Earth isn’t static: it’s dynamic, with erosion and continental drift wiping out really old craters. Only a few survive now, the ones that happened to be in very stable locations like this one. Studying them is like having a direct line to the past, though muffled by time and change. Still, it’s an amazing look into what things were like before life took hold on land all those eons ago.

Oh, one more thing: if the name is familiar, it should be. It’s named after Eugene Shoemaker, a geologist who was a pioneer in studying and identifying impact craters like this one. He died in 1997 in a car accident in Australia, so it’s fitting a crater there was named in his memory.

Image credit: NASA

Related posts:

Raising an impact in Africa
New study finds giant impacts aren’t periodic
"Amateur" geologist finds a South American crater
Deforestation reveals an old scar
Terra spots an impact on, um, Terra

As from above, so from below

By Phil Plait | January 10, 2012 7:00 am

NASA’s Earth Observatory site just put up this amazing picture. I have to say, this is one of the cooler pictures from the International Space Station that I’ve seen. Not for it’s beauty or anything like that — though it is starkly lovely — but because of what it shows:

[Click to dicraternate.]

Obviously, that’s a volcano on the right: Emi Koussi, in northern Africa. But look to the left, almost at the edge of the picture. See that faded ring? That’s Aorounga — an impact crater, some 10 – 15 km wide, formed when a chunk of cosmic debris hit the Earth about 300 million years ago! So these are two craters, one formed from processes happening deep below the Earth, and one from events from far above. Yet both can be seen at the same time, from one vantage point: orbiting our planet somewhere above the surface but beneath the rest of the Universe.

Image credit: NASA

Related posts:

A long, thin, volcanic plume from space
UPDATE: more amazing Nabro volcano images
Staring down an active volcano’s throat
Volcano followup: pix, video

CATEGORIZED UNDER: contest, NASA, Pretty pictures

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