Vredefort Crater, the world’s oldest and largest known impact structure | Hacker News Reader

Vredefort Crater, the world’s oldest and largest known impact structure

earthobservatory.nasa.gov

I grew up in the town called Parys on the map in the article. Besides creating some lovely hikes and river rafting there are also some very interesting rock phenomena that can only be seen in this area in the whole world.

I was just in Klerksdorp on business and I drove through Potch. I should have taken a detour to investigate.

Can you share some examples? I wonder if my own searching will reveal many.

Not from Parys but used to be a regular visitor: one example is streaks of obsidian in the rocks from the explosion which I believe is unique.

I read that and thought that it would be an excellent spot to prospect for gold, then it turns out that this is already the source of 1/3rd of all the gold mined on earth. Oh well, I'll have to wait for another good idea I guess.

Fun fact. The Vredefort Impact Area is roughly overlaid by a larger geological feature called the Bushveld Igneous Complex, which is from a totally unrelated geological event but resulted in this area having 60% of all the platinum and palladium in the world. So South Africa is stupendously geologically lucky twice over.

Or another asteroid to hit

If you're interested in impact craters, I recommend the book "Traces of Catastrophe" by Bevan M. French. You can read it here:

https://www.lpi.usra.edu/publications/books/CB-954/CB-954.in...

> impact was so strong that a 25-kilometer section of Earth’s crust was turned on end

This makes it sound like there was a 25km tall piece of crust sticking up into the air, at least for a moment. Is that really what happened or did I interpret "on end" wrong?

> Is that really what happened

No, that seems to be unlikely. But the impact may well have ejected soil into space, as far as I understand, and liquefied stone in its wake, whatever that means.

I think you’re interpreting the “25km” part incorrectly. It could be a 25km long, x m wide stretch that’s turned to form a 25km long, x m high ‘wall’.

At this point, I'm purely splitting hairs, but I would probably have said "turned on its side" or some other variation of "side" instead, because "end" means something different to me.

But obviously what you're saying makes way more sense physically, so that has to be what it is.

I wonder if the asteroid brought any rare materials.

Kinda disappointed nobody could figure out how big this was originally. Yes, we've lost a couple of soil layers to erosion, and yes the bottom has filled a bit with newer rock formations.

Still, you'd have to think we could estimate how big an object would need to be to carve out that much bedrock, assuming a given amount of topsoil.

Two billion years is a lot of time to wipe out useful clues.

I know, but the bedrock is unlikely to have changed that much. You could make a ballpark estimate on the mass and energy needed for that alone.

Still, I understand the top layer composition matters a lot in terms of how it could absorb an impact. Was it full of water? Earth? Sand?

> but the bedrock is unlikely to have changed that much.

We're talking about the time before the continents had formed, the scale we are looking at here is non-intuitive.

At that level of impact energy everything starts to behave like a fluid, even planet earth, so whether or not the top layer composition was water, soil, sand or rock is not that important. What's amazing is that there are traces left that much later, even more how large those features are. That's a testament to how enormous the impact must have been.

Here's the only reliable looking page I could fine : http://www.hartrao.ac.za/other/vredefort/vredefort.html

Original impact crater estimated to be 300Km in diameter. They think 70 cubic KM of soil was vaporized. For comparison's sake Mt St Helens explosion vaporized 1 cubic KM of soil and rock. Chixculub crater is 150Km in diameter, much much newer, but completely buried.

2 billion years old? I wonder if it had any impact on the Huronian glaciation which occured roughly at the same time...

That's amazing considering that pangea was created 270 million years ago and broke apart 200 million years ago.

Reply on news.ycombinator.com