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Author Topic: The Earth is 4 1/2 billion years old?  (Read 1872 times)

Offline Gordian Knot

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The Earth is 4 1/2 billion years old?
« on: 28/09/2012 14:28:18 »
Not questioning the time. A curious comment came up in a discussion last night with some friends. When we say the Earth is that old, at what point in Earth's creation are we talking about?

Did the Earth start forming from minuscule pieces of dust and debree 4 1/2 billion years ago? Or do we start the age count after the Earth was more less fully formed?

Pre Thera? Post Thera?

In what stage of its creation was the earth at the "beginning" that we say was 4 1/2 billion years ago.


 

Offline damocles

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Re: The Earth is 4 1/2 billion years old?
« Reply #1 on: 29/09/2012 22:44:19 »
The dating methods that give the age of the Earth as 4.5 American billion years (4500 million) are based around the age of zircons from Western Australia, which are the oldest fragments of solidified rock that have survived from the beginning. Most of the dating methods used for very old rock provide the date when the material last became solid and trapped the contents immobile.
http://en.wikipedia.org/wiki/Oldest_dated_rocks

Zircons are particularly good material for dating because both uranium and thorium have very similar chemistry to zirconium and hafnium, especially thorium. Their affinity for zirconium minerals is much greater than that of lead, and they are nearly always present as significant components of zircons, and the lead in zircons is nearly all radiogenic. (There is a way of correcting for "original lead", because lead-204 is not a product of any radioactive decay chain).

 

Offline Phractality

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Re: The Earth is 4 1/2 billion years old?
« Reply #2 on: 29/09/2012 23:11:14 »
I think you mean Theia, not Thera. According to the Giant Impact Hypothesis, the collision occurred about 4.53 billion years ago. Both planets were still hot from their formation, and the energy of impact would have vaporized most of both planets. It is unlikely that any crystals survived the impact. So the atomic clocks in the oldest crystals could not have begun counting until the Earth's crust solidified after the formation of the Moon.
 

Offline yor_on

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Re: The Earth is 4 1/2 billion years old?
« Reply #3 on: 04/10/2012 17:13:32 »
Well, it's about measuring radioactive decay in the oldest rock we found, right? I wonder if that means that it is rock that have wandered upwards from the inner of Earth in tectonic upheavals, if so can we define them to some depth? Read about using atomic devices for taking 'pictures' of Earths inner. The Russians, who loved the idea of using atomic weapons as their new digging tool, did some remarkable surveys in the proceedings of that as I understood. I feel sorry for those living in those areas today btw. Makes me wonder how long we will allow id** and arse lickers to be the ones deciding a civilizations direction? Because, we're all belonging on one small world, and we're all one civilization, the human one.
 

Offline damocles

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Re: The Earth is 4 1/2 billion years old?
« Reply #4 on: 06/10/2012 03:01:54 »
Well, it's about measuring radioactive decay in the oldest rock we found, right? I wonder if that means that it is rock that have wandered upwards from the inner of Earth in tectonic upheavals, if so can we define them to some depth? Read about using atomic devices for taking 'pictures' of Earths inner. The Russians, who loved the idea of using atomic weapons as their new digging tool, did some remarkable surveys in the proceedings of that as I understood. I feel sorry for those living in those areas today btw. Makes me wonder how long we will allow id** and arse lickers to be the ones deciding a civilizations direction? Because, we're all belonging on one small world, and we're all one civilization, the human one.

Whether or not you accept the Theia theory -- and it is only one of several viable rivals for formation of the Earth/Moon system -- it is almost certain in any of the theories that the whole Earth was a rather viscous liquid at an early stage, and that solidification began with formation of a crust on the outside due to falling temperature, and with a solid core at the centre due to extreme pressure.

Of the metallic elements, some can be very strongly bonded to oxygen. They form oxides and related compounds (can be regarded as "mixed oxides" -- silicates, aluminosilicates, etc.) to make rocky sorts of material, with relatively low density. These elements are known as "lithophiles". Other elements (known as siderophiles) are less strongly bonded to oxygen, but are soluble in the molten iron that was gravitating towards the core. Zirconium is a lithophile. It is not a very common element, but zircon has a higher melting point (2715 C) than the main lithophile oxides (silica 2230 C -- quartz, alumina 2035 C -- corundum, titania 1830 C -- rutile), and a relatively low solubility in the mixed melt. It will form separate crystals as the surface is cooling, incorporating chemically compatible dioxides of hafnium, thorium, and uranium into its structure.

So the uranium and thorium present in zircons is not anything to do with human playing around with radioactive elements; it is just one place where the uranium and more particularly thorium that is present in all rocky material gets concentrated.
 

Offline yor_on

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Re: The Earth is 4 1/2 billion years old?
« Reply #5 on: 07/10/2012 15:54:38 »
No I didn't mean that Damocles, but a interesting read just the same :) It was just me remembering how the Russians were doing very deep surveys inside the earth, using shock waves from atomic explosions, getting some exceptional data of the structures, as I remember. What I was wondering was if that oldest rock once came from the inside of Earth?
 

Offline grizelda

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Re: The Earth is 4 1/2 billion years old?
« Reply #6 on: 07/10/2012 21:44:07 »
Probably the idea is that the oldest rock (whether it has been found or even still exists) would be one which crystallized out of a melt somewhere on earth rather than a pre-existing crystal from a meteor or rock which came together to form the earth.
 

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Re: The Earth is 4 1/2 billion years old?
« Reply #6 on: 07/10/2012 21:44:07 »

 

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