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Author Topic: How do we know the age of the Earth?  (Read 7284 times)

Alex Hofmeyr

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How do we know the age of the Earth?
« on: 21/05/2010 06:30:04 »
Alex Hofmeyr  asked the Naked Scientists:
   
I listen to your show in Cape Town on CapeTalk.

I have had a couple of discussions with a friend of mine who is a creationist, and they seem to believe that the world is no more than a few thousand years old.

Now, even though this seems crazy to me and goes against everything that I've learnt, when you actually get into a discussion in this regard it is actually quite hard to come up with concrete proof against this.

Obviously we have carbon dating etc. but it appears that these methods are all mainly based on quite a lot of assumptions and extrapolations and not necessarily direct measurements.

Is there any proof that can be presented that not points to the actual age of our planet, but rubbishes the claim that the earth is only a few thousand years old?
 
As I say, I'm not sure if I can direct the question like this, but trying anyway...
 
Regards,
 
Alex Hofmeyr

What do you think?
« Last Edit: 21/05/2010 06:30:04 by _system »


 

Offline RD

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How do we know the age of the Earth?
« Reply #1 on: 21/05/2010 07:16:41 »
Continental drift is approximately an inch a year, how many inches between Africa and South America ?.


« Last Edit: 21/05/2010 07:40:16 by RD »
 

Offline chris

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How do we know the age of the Earth?
« Reply #2 on: 21/05/2010 09:11:37 »
That's an elegant answer, RD.

I was going to suggest uranium / lead dating, whereby the ratios of uranium isotopes to their lead decay products can be used to date an object. The very long half lives involved (4.5 billion years and 700 million years for the two decay pathways that scientists use) are on par with the age-scale of the planet and therefore very useful for ageing the Earth.

Chris
 

Offline LeeE

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How do we know the age of the Earth?
« Reply #3 on: 21/05/2010 16:29:47 »
While they cannot give the absolute age, dendrochronological records prove that the Earth is more than just a 'few' thousand years old (If these people are using Ussher's date for the creation then they're claiming that the Earth is no more than 6014 years old).

From: http://en.wikipedia.org/wiki/Dendrochronology#Growth_rings

Quote
Fully anchored chronologies which extend back more than 10,000 years exist for river oak trees from South Germany (from the Main and Rhine rivers).  Another fully anchored chronology which extends back 8500 years exists for the bristlecone pine in the Southwest US (White Mountains of California)

...and...

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In 2004 a new calibration curve INTCAL04 was internationally ratified for calibrated dates back to 26,000 Before Present (BP) based on an agreed worldwide data set of trees and marine sediments.
 

Offline FuzzyUK

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How do we know the age of the Earth?
« Reply #4 on: 30/05/2010 12:21:04 »
Continental drift is approximately an inch a year, how many inches between Africa and South America ?.

But that is based on an assumption that drift occurs at a linear rate. But could the rate of drift be non-linear?
 

Offline Mazurka

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How do we know the age of the Earth?
« Reply #5 on: 04/06/2010 14:41:16 »
Continental drift is approximately an inch a year, how many inches between Africa and South America ?.

But that is based on an assumption that drift occurs at a linear rate. But could the rate of drift be non-linear?
  Absolutely - although it is a wonderful piece of lateral thinking and a readily understood way of suggesting that the world is older than some religions suggest, spreading centres are producing new crust at different rates - this is a factor that causes stress to build up in the crust leading to earthquakes in vulnerable areas.

Geologists infer the age of the earth from the oldest rocks found on earth (Australia) and from the ages of meterorites and lunar samples.  There are a lot of assumptions about the formation of the solar sysytem, but there are a lot of indiviudal bits of evidence that corroborate the current paradigm.

More simply put, the earth is at least 4 billion years old.  This figure has been arrived at by radiometrically dating Zircon crystals from the oldest known/ accessible rocks in the world.

Zircons are particlarly useful for dating as they are highly stable and resistant to weathering.  When Zircons form they contain measureable quantities of Uranium - but importantly do not contain lead.

Broadly Uranium undergoes radioactive decay to lead and by measuring the rations between the various isotopes (using some form of mass spectrometer) it is possible to arrive at a fairly accurate date.  To improve accuracy many zircons from a particular sample of rock would be analysed to produce an average figure.   
« Last Edit: 04/06/2010 14:42:58 by Mazurka »
 

Offline stereologist

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How do we know the age of the Earth?
« Reply #6 on: 04/06/2010 20:05:37 »
There are also things called varves. These are layers that can be observed in lake bottoms. Particles during the summer are large and in the winter even the finest particles begin to drop out if the lake is completely frozen. There are places in the world where 13,000 varves have been counted.

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

There have been continuous varves counted in Japanese lakes that are over 29,000 varves in all.

Here is the important part about varves:
1) They show that the Earth is much older than 10,000 years.
2) They show no effect from a global flood.
 

Offline JimBob

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How do we know the age of the Earth?
« Reply #7 on: 05/06/2010 17:33:41 »
AND - varves go back a LOOOOONG time. Banded iron formation several billion years old are also varves as they were PROBABLY deposited in a lacustrine environment.
 

Offline Bass

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How do we know the age of the Earth?
« Reply #8 on: 06/06/2010 05:31:49 »
AND - varves go back a LOOOOONG time. Banded iron formation several billion years old are also varves as they were PROBABLY deposited in a lacustrine environment.

Really?  How do you account for the source of the iron  For precipitation of silica?  The tremendous size of some BIF's? Too many other factors don't fit a lucustian environment.

While BIF's are still a controversial subject, most research points toward either deep oceanic or continental shelf deposition, with submarine hydrothermal activity as source for the iron.
 

Offline JimBob

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How do we know the age of the Earth?
« Reply #9 on: 06/06/2010 20:24:14 »
Please refer to the word "probably" - It is an explanation I have heard bandied about. I am not infallible, although most believe I am :-)
 

Offline stereologist

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How do we know the age of the Earth?
« Reply #10 on: 07/06/2010 03:17:44 »
Another dating method that points to an older earth is the themoluminescence method. It involves getting a piece of quartz in the dark. While dark, either in pottery, or buried by sediments, electrons can get trapped inside of the crystal. The grain is heated and light is released as the electrons are allowed to escape the trap. The intensity of the released light is used to determine how long the grain has been in the dark.
http://en.wikipedia.org/wiki/Thermoluminescence_dating
 

Offline daveshorts

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How do we know the age of the Earth?
« Reply #11 on: 07/06/2010 12:43:19 »
One of the older ways of dating the earth was to look at the rate of heat loss through the crust and the rate at which the temperature changed with depth. Lord Kelvin assumed that the earth started off all at the same temperature and it is the same stuff all the way through and got an age of about 10 million years.

This was radical for the time, but a huge underestimate, because the temperature gradient in the crust is much higher than it should be because the mantle is convecting so the temperature gradient in that is much smaller, and of course he didn't know about radioactive decay which is a major heat source for the earth.

Fundamentally there is an immense amount of evidence for the earth being very very old, however if you assume an omnipotent creator, you can always say the universe was created 3 seconds ago to look like it is billions of years old.  If this was actually the case then it says something very peculiar about the creator...
« Last Edit: 07/06/2010 12:47:35 by daveshorts »
 

Offline Mazurka

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How do we know the age of the Earth?
« Reply #12 on: 08/06/2010 16:15:43 »
Please refer to the word "probably" - It is an explanation I have heard bandied about. I am not infallible, although mostly I believe I am :-)
[:0] ;)
I must admit I had been thrown up to belive that it was the sea rather than lakes where BIF formed, but it seems reasonable  that they reflect some sort of seasonal variation in O2
 

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How do we know the age of the Earth?
« Reply #12 on: 08/06/2010 16:15:43 »

 

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