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


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Impact

Comments (41)

Links to this Post

  1. Lonar crater summer getaway | Go Trek | March 24, 2012
  1. Mike

    Deep Impact South, mate.

  2. (Now to insult all the aussies reading this blog)
    Thats no crater, that is where the tried to dig their way back to England.

  3. Pete

    Well, am I amazed! As an Australian, I was under the impression that we only had the one impact crater, Wolf Creek, but boy was I wrong. Regardless, as a geology student, studying such landscape features is an aspiration which I hope will, one day, come into fruition.

  4. Bubba

    So who was Teague, and why did he lose the credit?

  5. Messier Tidy Upper

    Great image – thanks. :-)

    Reminds me of the Acraman Crater relatively recently discovered in my own state of South Australia :

    http://en.wikipedia.org/wiki/Acraman_crater

    which is of a fairly similar vintage.

    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.

    This Carl Sagan “cosmic year” timeline analogy :

    http://palaeos.com/time/cosmic_calendar.html

    may help put this & the rest of Earth’s long prehistory and exceedingly super-uber breif history into perspective. I hope. :-)

    Really minor nit to pick :

    That’s Shoemaker (formerly Teague) Crater

    Actually it was formerly the Teague Ring according to :

    http://en.wikipedia.org/wiki/Shoemaker_crater

    &, whilst I don’t know for sure, I suspect the answer to (#3) Bubba’s question is that Shoemaker was the one who identified it as an impact crater. BTW. Teague gets a type of granite honouring her or his name so she or he doesn’t totally miss out. :-)

  6. Nigel Depledge

    The BA said:

    It may be as young as 570 million years, . . . 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,

    This is not very accurate. If the crater is as young as 570 million years, then it’s roughly the time of the Ediacaran fauna, which were macroscopic soft-bodied animals, not microscopic. While it is true that this would have been millions of years before the first hard-shelled animals, you seem to be implying that animals went straight from microscopic soft bodies to macroscopic hard shells with nothing in between.

  7. I have a question… why is there no actual impactor at the bottom of the crater? Something big hit, enough to form a crater that lasts over a billion years, so why is there no sign at all of the thing that caused the crater? Same for all those uneroded craters on the moon, or Mars. Not a sign of the impactor anywhere!

  8. Chief

    How about the large crater at Sudbury Ontario Canada.

  9. And then there’s Dalgaranga crater in Western Australia. At just 25 metres in diameter, it is Australia’s smallest (so far) known crater:
    http://www.yalgoo.wa.gov.au/AttractionDetails.aspx?trmID=20

    Discovered when a station hand accidentally rode into it, so the story goes. Estimates of its age also vary greatly, but an impact does appear in local Aboriginal lore and some have placed the time of impact as recently as 3000 years ago. It’s not even big enough to be clearly visible in Google Earth!

  10. Tom Ogletree

    Looks like a golf course in and around it. very cool

  11. He’s also the Shoemaker part of the Shoemaker-Levy 9 comet that hit Jupiter in the early 90s.
    @ Alex (#7): I would venture that the original impactor is buried under debris. In some cases the impact itself pulverizes or melts the object.

  12. Messier Tidy Upper

    @7. Alex Hall : Probably because the impacting object was totally vapourised & completely destroyed in the impact? ;-)

    @4. Bubba : “So who was Teague, and why did he lose the credit?”

    This website explains the second half of that :

    http://www.galaxyresources.com.au/projects_shoemaker.shtml

    The Shoemaker Meteorite Impact crater was previously known as the Lake Teague Ring Structure but was renamed the Shoemaker impact structure in honour of the late Gene Shoemaker and as a tribute to his and Caroline Shoemaker’s work on Australian impact structures.

    Plus gives a geological map of the structure. This paper :

    http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/18924/1/98-0040.pdf

    notes that the original Teague name came from nearby Mount (hill) and (salt) Lake Teague. It was “informally” named that by Butler in 1974 and has a little more info on the crater /ring system itself; a lot of it in geologese.

    Unfortunately, I can’t really find anything definitive on who or what Teague was for you. :-(

    There was an Aussie politician – Senator Baden Teague (another South Aussie too!) whose bio is on wikipedia but I cannot determine whether the Ring was named in his honour or has any connection with him.

    @3. Pete :

    Well, am I amazed! As an Australian, I was under the impression that we only had the one impact crater, Wolf Creek, but boy was I wrong.

    Yep. See :

    http://www.passc.net/EarthImpactDatabase/Australia.html

    for a list of many more examples with photos and more info. :-)

  13. Scott P.

    A question: I always imagine that when a large body hits, the meteorite and the ground that it slams into is basically pulverized, and that the crater ring is more or less a huge mass of loose rubble. But surely an uncompacted heap of rock and dirt wouldn’t persist for half a billion years. How exactly was the crater rim formed?

  14. Regner Trampedach

    Alex Hall @ 7 and Scott P. @ 11: I am afraid you fail to appreciate the energies involved in asteroid impacts. The impactor melts completely and a good chunk of the impacted ground melts and together they form the crater of the mixed material. The cooled solidified rock is rather hard.
    Cheers, Regner

  15. dave chamberlin

    The subject raises an interesting question which I have no answer for and hope it can be answered by others. Is there a graph showing the decrease in earth impacts going back in time. It interests me from a history-biological point of view. Why did earth only get moving with the Cambrian Explosion 7/8ths of its way through the history of life on planet is a complicated question that might in part be due to a slower decrease in earth impacts IF this graph shows a slow decrease from earths beginning. But I have no clue if such a graph exists or if one does it is accurate. Anybody?

  16. dave chamberlin

    A second question related to the first one would be to look at the moons craters dating them in age and then use that graph as one to apply to the earth. Afterall the earth has a long and irratating habit of erasing it’s past history while the moon is a highly cooperative historian.

  17. It looks like a multimedia art with – with fabric, beads, and impasto paint.

  18. HvP

    Alex Hall asked, “why is there no actual impactor at the bottom of the crater?”

    That’s like asking why no one finds the remains of a nuclear warhead at the center of an atomic blast. The explosion released in a meteor impact of this scale is equivalent to several (hundred? thousand?) nuclear warheads all detonating in the same place.

    Consider that when we sent our own impact probes to slam into a comet that the solid slug was complete vaporized by the explosion.

  19. Bill

    @dave chamberlin

    Is there a graph showing the decrease in earth impacts going back in time?

    There have been two recent colloquium talks @ http://www.seti.org/talks on just this subject. The first is by Don Lowe discussing spherule deposits (small round sand sized objects created by a large impactor) laid down about 3.5 Gyr ago. At the end of the talk, he does relate the rate of impactors to the basin forming impacts on the moon. A subsequent talk by Bill Bottke covers the Late Heavy Bombardment and as well as some of the recent modelling of the formation of the solar system (the Nice Model, etc). From a biological point of view, the interesting observation is that the last of the string of large impactors coincides with the accumulation of oxygen — coincidence? Perhaps, but I recall a lecture on the chemistry of the oceans and the effects of large impactor events but I don’t have the time now to look up the talk (I think it was one of the NASA Astrobiology Institute webinars).

  20. 11 Scott P: A question: I always imagine that when a large body hits, the meteorite and the ground that it slams into is basically pulverized, and that the crater ring is more or less a huge mass of loose rubble. But surely an uncompacted heap of rock and dirt wouldn’t persist for half a billion years. How exactly was the crater rim formed?

    The thing about such hypervelocity impacts is that even materials like steel or rock act like liquid at these speeds. This is the principle behind many armor-penetrating tank projectiles. When they run a super slow motion simulation of an APDS (armor piercing) round impacting solid steel, it looks very much like a drop of viscous liquid falling into another viscous liquid. The same applies (much more so, in fact) to meteors. The crater rim is like the ripple formed by a drop of rain hitting a puddle.

  21. @15 Jen Deland: Heh, that’s true, actually. As craters go, she’s a pretty one :)

    For anyone in the US (or anyone planning on visiting on vacation), you’ve got to check out the unimaginatively named Meteor Crater in Arizona. It’s a relatively young, only about 50,000 years old, and about 2 kilometers across. My folks took me there when I was maybe 7 years old, and I can still remember it. It was one of the experiences that really first sparked my curiosity for space.

    I actually have a picture of meteor crater on one of my credit cards. I figured that an enormous hole in the ground was a good visual metaphor for my financial situation ;)

  22. MadScientist

    That’s funny – I saw Australia and ‘impact site’ and I thought of Gene Shoemaker all those years ago and stories about an impact crater so large that it’s best seen from satellite photos. I didn’t realize a crater was renamed Shoemaker. I guess you just can’t mention meteorites without Gene Shoemaker coming up.

  23. Wzrd1

    @20, Joseph G, actually, tank penetrators VAPORIZE, some to the point of becoming plasma, which causes far more destruction than liquid metal or a solid projectile, due to multiple fires starting inside of the tank (which the ammunition greatly resents).
    The same is true of hyper-velocity impactors, that is how the impacted area instantly turns liquid (OK, a bit MORE complicated, as shockwaves moving at supersonic velocities in solids generates a tremendous amount of heat too, along with the compression effects, all dissipating the energy of the impactor.
    I once saw the equations for those tank penetrators, you’d be shocked how much math goes into making one! And how easy it is to defocus the jet, which is why the US Army Stryker vehicles have those slat panels on the side, to prematurely detonate any RPG fired at them.

    @Messier Tidy Upper, I’d be surprised if there aren’t MORE impact craters that are hidden by erosion over time, you ARE on a generously sized continent. :)
    I’ve always been surprised how many meteorites have been witnessed (and found) in the middle east. One would think that they’re a meteorite magnet, but then, one need only consider the size of area, how spread out the populace has historically been and how sparsely the rest of the world is.
    It makes one wonder how many impact in the Gobi…

  24. Messier Tidy Upper

    @ ^ Wzrd1 : Yep. We’re also on a very old and eroded continent which is mostly desert or semi-arid so I’d be surprised if there weren’t a lot that have since been eroded away entirely or buried and lost.

    Incidentally, I gather that Antartica is apparently the best place in the world for finding meteorites – they stand out well against the snow & with few people or creatures to disturb them are in the most pristine state. If memory serves the ALH (numbers) martian meteorite with the controversial possible nano-fossils was found there among others.

    .. 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).

    You know that by choosing Sydney you’ll have made the Victorians jealous you didn’t vapourise Melbourne instead right? ;-)

    State rivalry here is pretty strong – the reason why Canberra is our nation’s capital – they couldn’t choose between Sydney or Melbourne so it was the compromise creation to avoid a conflict between (then) colonies.

  25. agenoria

    I haven’t seen Bad Universe (I’m in the UK), but I’m curious – did you mention this album cover?

    http://oilbase.deadheart.org.uk/faqs/red.sails.html

    It’s Midnight Oil’s “Red Sails In The Sunset” and has craters by both Sydney Opera House and the Harbour Bridge.

  26. Wzrd1

    @Messier Tidy Upper, your memory serves you well, let’s face it, meteorites don’t come in white, so they stand out quite well in Antarctica. :)
    I wonder what ground penetrating radar would see on the Australian continent? I’d bet those eroded craters would stand out like a man in a convent!

    State rivalry pops its head up here in the US too, as well as regional rivalry. That’s why they took a swamp, backfilled it and named it Washington, D.C. Right between the north and south. And there are still hard feelings in the South for their being trounced in the civil war. ;)
    But then, there is this legend about how the first two brothers didn’t get along and one killed the other. Rather explains some habits of the species well… :/

  27. Simon says

    Pete; this is interesting for Google Earth to see where all the craters are in Australia (and worldwide). I found it easier because it gives the info in 3d with location etc

    http://bbs.keyhole.com/ubb/ubbthreads.php?ubb=showflat&Number=1211741

  28. Scott P.

    “I am afraid you fail to appreciate the energies involved in asteroid impacts. The impactor melts completely and a good chunk of the impacted ground melts and together they form the crater of the mixed material. The cooled solidified rock is rather hard.”

    If you end up with a bunch of liquid rock at high temperature, why doesn’t it spread out until you get a big flat puddle of molten rock? Why do you get a ring range? I would think that much liquid rock must take years, if not decades, to cool enough to solidify.

  29. (Now to add insult to the English reading this blog)

    It’s actually where we filled the hole in so no more of you arrive :D

    Amazing stuff though, wonder if we will experience any large impacts in out lifetime. I thought Wolf Creek was our only crater also. hmmm.

  30. I simply can’t imagine a 6 mile wide meteor being completely vaporised at impact… I know scale is a massive thing, but if part of it is still poking out of the atmosphere surely there’s not enough energy to completely destroy the whole thing? Or is my imagination just not big enough yet?

  31. JB of Brisbane

    Hey, what gives? The image above is different from the one I saw this morning… or is it?

  32. Nigel Depledge

    @ Scott P (28) –
    Well, I don’t know for sure, but I can take a guess. Or guesses:

    1) It probably does not take much time for most of the liquified rock to cool down enough to become very viscous. Some types of lava eruptions are pretty viscous and gloopy even at their hottest.
    2) You’re sure to have a gradient of temperature from the point of impact outwards, so at some point it’ll be hot enough to be liquid but not hot enough ever to get runny.
    3) Rock is a fluid anyway – at least, it behaves thusly when considered over long time periods (the only way to model plate tectonics is to treat the Earth’s crust as a viscous liquid). It may not ever need to melt to transmit a large transverse wave.

  33. Nigel Depledge

    @ Alex Hall (29) –
    Supersonic shock waves cause a lot of heating.

  34. Peter B

    Scott P @ #28 asked: “If you end up with a bunch of liquid rock at high temperature, why doesn’t it spread out until you get a big flat puddle of molten rock?”

    It doesn’t spread out to form a puddle because the strength of the shock wave caused by the impact is sufficient to blast material out for tens, hundreds or thousands of kilometres, or even into orbit. It’s the difference between pouring water out of a plastic bottle onto the ground, and dropping the full bottle onto the ground from the top of a building.

    “Why do you get a ring range?”

    The raised rim is caused by compression of the rock surrounding the impact site. The rock is close enough to the impact site to be slightly softened by the heat of the impact and compressed by the shock wave generated by the impact. The rock is shoved outwards, but before it can settle back it cools sufficiently to solidify again.

    “I would think that much liquid rock must take years, if not decades, to cool enough to solidify.”

    Why should liquid rock take years to solidify? Lava is liquid rock and it generally cools solid in a few days at most.

    Can I recommend you read the Wikipedia article on Impact Craters? It answers your questions better than I can. But in summary, I think you’re missing the sheer amount of energy released by these sorts of impacts. They’re incredibly fast and incredibly violent.

  35. Peter B

    Alex Hall @ #30 said: “I simply can’t imagine a 6 mile wide meteor being completely vaporised at impact… I know scale is a massive thing, but if part of it is still poking out of the atmosphere surely there’s not enough energy to completely destroy the whole thing?”

    What do you mean by saying a 6 mile rock would be still poking out of the atmosphere at impact? The Earth’s atmosphere is much deeper than that. Six miles is only a little higher than the top of Mount Everest – at that altitude there’s still just enough oxygen for people to stay alive.

    “Or is my imagination just not big enough yet?”

    This might be the problem. :-)

    The important thing to keep in mind is speed. These rocks hit the Earth at speeds something like ten times faster than bullets, and possibly more. That’s the difference between you walking down a path and a car driving down a suburban street. And remember energy is proportional to the square of the speed. Something that big travelling that fast is going to release a lot of energy when it hits.

  36. Lost in this discussion is the fact that the Earth’s surface is 3/4 water. There are no doubt many more impact craters under our oceans’ surfaces (though a crater probably wouldn’t survive very long under water).

  37. Wzrd1

    Lugosi has a point, ocean bottom remodeling from tectonic activity does tend to erase any impact craters under the ocean. And most impactors that WOULD reach the ocean would tend to not create a crater, due to size.
    Meanwhile, debate, rather than sampling and study surrounds most oceanic craters, such as Silverpit, Shiva and a few others. After all, drilling for oil is far more important than silly endeavors like science, right? :/

  38. @23 Wzrd1: @20, Joseph G, actually, tank penetrators VAPORIZE, some to the point of becoming plasma,
    Weird. I wouldn’t have thought there was enough energy to vaporize something that size (especially made of tungsten or DU)!
    But there ya go. Things aren’t really intuitive at these kinds of nutty energies :)

  39. @24 MTU: Yep. We’re also on a very old and eroded continent which is mostly desert or semi-arid so I’d be surprised if there weren’t a lot that have since been eroded away entirely or buried and lost.
    I recall seeing some kind of documentary on the geological history of the Earth, and the geologist traveled to Australia, saying that the oldest exposed rocks on Earth were there. Something like 4 billion years old!

  40. Matt B.

    “continental drift wiping out really old craters”

    It would be really amazing to find a crater half gone at the edge of a subduction zone.

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