back to article Early Earth’s ‘golden shower’

Rocks from Isua in south-west Greenland have been hailed as providing evidence for what geologists believe is the source of complex and heavy elements on Earth: an asteroid shower that endowed our young planet with gold (as well as platinum, iridium, nickel and tungsten). The research to be published in Nature suggests that the …

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Happy

Only El Reg could use "golden shower" in a science story headline

Keep up the good work.

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Facepalm

@Mahatma Coat -- A shower? Hardly!

A shower? Hardly!

Wouldn't want to be around at the time.

Journos can't help themselves but I'm surprised it wasn't

"EARLY EARTH'S 'GOLDEN SHOWER' WITH THE MIDAS TOUCH".

Duh...

...El Reg's slipping.

>:-)

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Boffin

Re: Hardly?

Just a suggestion. Type the words "golden shower" into your favoured image or video search engine.

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Coat

Are you taking the...

... oh, sorry, *that* sort of gold!

Nothing to see, move along...

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Facepalm

I am confused......

I was thinking how I would explain this to my wife realising I would say 'well, they date the rocks....', which then did not make sense.

Surely, dating is the way to resolve this.

If 'gold' is dated to 3.9byo, then it is not a likely option, though not impossible.

If gold, and nickel and cadmium etc turns out to be , say 7.5byo,, then the asteroid answer sounds fine......

Or am I talking tosh as usual ?

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Boffin

You can only use radiocarbon dating...

to date things which contain a certain predictably-decaying isotope of carbon.

You can't just 'date' a lump of gold or other metal.

There is also a discussion about the accuracy of this method as some evidence suggests we may need to adjust for changes in 'predictable' patterns over geological timescales.

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Facepalm

Still Confused... @Your Retarded

And this is where I get more confused.....

Gold [au] has atoms. Obviously.

It has protons, electrons and neutrons. But it also has isotopes. I know it is not carbon, so I was not suggesting "carbon dating" but, was thinking of "other dating", in the same way that other non carbon "things" are dated.

Or, is this where I am going wrong : one can only date using carbon ??????

Still confused.

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Ru
Boffin

Re: "one can only date using carbon ??????"

Not at all. There are various colours and flavours of radiometric dating, suitable for different ages and levels of accuracy. Have a peek at http://en.wikipedia.org/wiki/Radiometric_dating if you're bored.

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You can only radiodate radioactive isotopes

And if you want to date multi-billion-year-old isotopes, then you need multi-billion-year half-lives.

They mostly use Uranium/Lead or Thorium/Lead dating for things this old.

Radiodating measures the ratio of undecayed radioisotope to decay products, compares it to the half-life and then works out how long it's been. But this only works if the decay products are still stuck in the rock, ie there hasn't been a chemical process to separate them out.

Uranium that decayed before the rock was formed (ie in the asteroid) will have been separated out when it all melted when the asteroid hit earth. What you're measuring with radiodating is the length of time since the rock was formed.

[Radiocarbon is different because there is new C14 formed in the upper atmosphere - what you're measuring then is how long it's been since the carbon was attached using photosynthesis in a plant; in practise, that's effectively the length of time since the animal you're looking at died]

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Radio dating

You're right about using radioactive decay of isotopes to perform dating, but where it falls down is that there aren't any isotopes of gold with half lives long enough to perform geological dating. So you have to make an assumption that the gold was present when the rock was formed (in the case of Isua when sediments were metamorphosed into gneiss) and use the radiodate established from other elements in the rock - IIRC the Isua was dated using rubidium strontium dating.

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Trollface

Testing the method

And you test the dating method by seeing how accurately it dates items you know, through documentation, the date of.

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Boffin

@Richard Gadsden -- Put some figure to it.

Put some figures to it.

Of all the uranium on earth, half has decayed to lead. And it took 4.5 billion years to do so!

(Uranium 238 half-life: ~4.47 * 10^9 years.)

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Devil

Not just that

If memory serves me right C dating is limited to a few hundred thousand years tops. The C14 halflife is not long enough to date prior to that.

Prior to that for the few M range you have to use K/Ar (pray for nicely solid rocks which do not release Ar) and for anything beyond a few M your primary choice are methods based on Pb isotope ratios (Pb mainline vs impurities from U and Tho alpha-decay products).

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Title

"New Scientist notes that there appears to be too little precious metals for the hypothetical bombardment to be a complete explanation."

New Scientist went on to ask for greater amounts of precious metals be sent to their offices for comparison purposes.

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Pint

Can We Backtrack And...

...locate a few of these gold asteroids?

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A.C. Clarke beat you to it

In 3001, he describes how people have been engaged in a search for the fabled "golden asteroid", which had become an urban legend of the day.

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Thumb Up

Dr Who beat you to it as well

cf. Dr Who Revenge of the Cybermen - Tom Baker 1975 - The fabled "planet" of gold - asteroid Voga

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Alien

If you want a planet made of gold

just order one from Magrathea

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@ Michael

Great idea, but unfortunately they are temporarily only taking orders from mice.

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Alien

True, but

They might be persuaded by the dolphins

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Holmes

Umm.. correct me if I'm wrong...

..but didn't ALL materials the Earth is made of arrive from space in the form of colliding objects?

It's purely a matter of when the objects arrived - early or late....

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Happy

Mr.

Doesn't sound very plausible to me. When's the last time y'all picked up a lump of gold that fell from the skies? Surely this should be happening all the time still?

Anyway, I'm definitely no scientist so maybe there are good examples around of golden meteorites. The ones I've seen were either made up of rock or iron. Must admit though that I probably wouldn't be in a hurry to report a meteor strike to the authorities if I woke up one morning and found my backyard covered in gold.

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Anonymous Coward

Plausible?

"When's the last time y'all picked up a lump of gold that fell from the skies? Surely this should be happening all the time still?"

It almost certainly is -- but since most of what comes through the atmosphere on a daily basis (more than 10,000,000 tons per year I think) is vaporised on entry, you're probably breathing it.

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Anonymous Coward

Isotopes ...

and their relative abundance in the sample should tell you where and when it came from. With Iridium it is particularly easy to identify if its terrestrial or extra-terrestrial in origin I believe.

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Happy

Golden asteroid, maybe

but someone *has* discovered a planet made almost entirely of diamond. Will that do?

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Coat

That was one from Magrathea too

mine is the one with a trilogy in 5 parts in the pocket

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Boffin

Absolutely not.

Have you ever tried to use diamond to build an electrical contact? And never, ever use it to conduct heat away from the CPU. It has to be a metal.

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Coat

Why gold is rare..

.. because most of the asteroids were made of Purest Green

I'm off

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Alien

origin?

So it seems that around 3.9 years ago this planet passed through a supernova remnant shock wave. I wonder if it's possible to find evidence of that supernova remnant still expanding, and track it back to the neutron star/black hole left behind by the supernova which gave us our gold?

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