Meteorite Age

Graeme
4StarLounger
Posts: 533
Joined: 11 Feb 2010, 12:23
Location: Medway, Kent, UK

Meteorite Age

I'm doing an astronomy course which I'm enjoying immensely. There was an assignment set for the first module which was on the subject of Planetary Science. We all handed in the assignment tonight so I haven't come here to ask anyone to do my home work for me! But whilst talking to the other people on the course it would appear that we all got differing results on a particular question about calculating the age of a meteorite!

Here's the question:

(b) Fig. 1 is a Sm-Nd isochron plot of the orthopyroxene mineral that makes up the bulk of the meteorite ALH84001.

(i) Determine the slope of the isochron.
(ii) Thus calculate the age of the meteorite. The constant for the decay of 147Sm, λ = 6.54 x 10-12yr-1.
Isochron Plot.png
Spoiler
(i) Slope = rise/run

= (0.518-0.51)/(0.4-0.12)

= 0.008/0.28

= 0.029

(ii) t = ln(m+1)/λ

= ln(0.029+1)/6.54*10-12

= 0.02859/6.54*10-12

= 175*106 years
My answer seems quite low for the age of a meteorite but the rock in question is acrondrite so it might not be. I would be interested to know what others here might make it.

Regards

Graeme
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HansV
Posts: 74138
Joined: 16 Jan 2010, 00:14
Status: Microsoft MVP
Location: Wageningen, The Netherlands

Re: Meteorite Age

If I calculate = 0.02859/6.54*10-12 in Excel, I get 4.37*109, or a bit over four thousand million years. That is slightly less than the age of our solar system (about 4.6*109 years).
Regards,
Hans

PaulB
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Posts: 1524
Joined: 26 Jan 2010, 20:28
Location: Ottawa ON

Re: Meteorite Age

42
Regards,
Paul

Rudi
gamma jay
Posts: 25393
Joined: 17 Mar 2010, 17:33
Location: Cape Town

Re: Meteorite Age

PaulB wrote:42
That's BobH's number...the answer for everything!

Graeme, your maths is a bit advanced for me so I'd rather eat Pi and look at shooting stars.
Regards,
Rudi

Graeme
4StarLounger
Posts: 533
Joined: 11 Feb 2010, 12:23
Location: Medway, Kent, UK

Re: Meteorite Age

HansV wrote:If I calculate = 0.02859/6.54*10-12 in Excel, I get 4.37*109, or a bit over four thousand million years. That is slightly less than the age of our solar system (about 4.6*109 years).
That's interesting, when I'm at work I only ever use a spreadsheet for maths, I don't use a calculator. My error was because I didn't use the calculator properly! I did 6.54 xy -12

175 million years seems too young and 4.6 billion years seems too old. I'll check the rest of the calculations using a spreadsheet! I only used a calculator because I didn't know how to do natural logs in Excel. Or I could just Google ALH84001.

Graeme
4StarLounger
Posts: 533
Joined: 11 Feb 2010, 12:23
Location: Medway, Kent, UK

Re: Meteorite Age

Rudi wrote:
That's not very likely!

Rudi wrote:
I'd rather eat Pi.........................
Pi day was last Saturday!

HansV
Posts: 74138
Joined: 16 Jan 2010, 00:14
Status: Microsoft MVP
Location: Wageningen, The Netherlands

Re: Meteorite Age

According to articles I found on Google, the ALH8001 meteorite does appear to be about 4 billion years old (give or take half a billion - peanuts!).
Regards,
Hans

Graeme
4StarLounger
Posts: 533
Joined: 11 Feb 2010, 12:23
Location: Medway, Kent, UK

Re: Meteorite Age

Likewise.

My assumption that an acrondrite meteorite is not as old as a crondrite is incorrect. It could have been knocked into space from the surface of Mars at any time. And I need to learn how to use a calculator properly!

Thanks Hans