# Can scientists determine the age of something older than the earth? **URL:** \ **Category:** Factual Questions\ **Created:** [July 14, 2008, 3:15am UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393 "2008-07-14T03:15:20Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [July 14, 2008, 3:15am UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/1 "2008-07-14T03:15:20Z")
Say meteorite fell that was a lot older than the earth. How could scientists date such an object? ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 14, 2008, 3:50am UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/2 "2008-07-14T03:50:52Z")
According to [this](http://www.meteoritestudies.com/protected_dating.htm), the decay of rubidium-87 into strontium-87 has a half life of 49 billion years, which should be ample, since it’s more than 3 times the estimated age of the universe. ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [July 14, 2008, 3:56am UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/3 "2008-07-14T03:56:05Z")
They have already found a meteorite that contained particles [older than the solar system](http://www.guardian.co.uk/science/2006/dec/01/uknews) ---
**Author:** ![Stathol](https://avatars.discourse-cdn.com/v4/letter/s/71e660/32.png) [@Stathol](https://boards.straightdope.com/u/Stathol)\ **Post date:** [July 14, 2008, 4:22am UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/4 "2008-07-14T04:22:20Z")
The meteorite Fubaya mentioned notwithstanding, the vast majority of meteorites are just fragments of asteroids from the asteroid belt. The asteroid belt - like everything else in the solar system - was formed about 4.5 billion years ago. So with that one notable exception, you basically won’t find any meteorites that are very much older than the earth. I did come across [this article](http://www.universetoday.com/2004/05/20/asteroids-change-colour-with-age/), though, which was kind of interesting. Apparently the surface of an asteroid gradually “weathers” in a way that causes a slight color change. If you crack one open, the interior is a different color until it has a chance to weather. When a larger asteroid gets fractured into smaller ones, you could theoretically “date” them in the sense of determining how long ago they broke off from the parent asteroid by examining their color. I’m not sure if it’s possible to do the same thing with a meteorite, since the outer surface has been subjected to quite a lot of heat. Also, in a more general sense, astronomical objects can be roughly dated based on their chemical composition. Pretty much everything heavier than hydrogen is the product of fusion reactions in stars. The heavier elements take longer to form, so you can get a rough idea of how old something is by the elements that are present. Or, at least, you can set an upper limit on its age. Ex., if a rock contains silicon; therefore, it can’t be any older than X years because silicon would not have existed in any significant quantity before then. ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [July 14, 2008, 12:16pm UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/5 "2008-07-14T12:16:34Z")
[QUOTE=astro] Say meteorite fell that was a lot older than the earth. How could scientists date such an object? [/QUOTE] Well, they did pretty well dating the age of the Universe: > **[Our Expanding Universe: Age, History & Other Facts](https://www.space.com/52-the-expanding-universe-from-the-big-bang-to-today.html)** > > The evolution and content of our ballooning universe That site discusses the size of the universe, but of necessity discusses the age as well. ---
**Author:** ![Alive\_At\_Both\_Ends](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@Alive\_At\_Both\_Ends](https://boards.straightdope.com/u/Alive_At_Both_Ends)\ **Post date:** [July 14, 2008, 12:35pm UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/6 "2008-07-14T12:35:24Z")
[QUOTE=Colibri] According to [this](http://www.meteoritestudies.com/protected_dating.htm), the decay of rubidium-87 into strontium-87 has a half life of 49 billion years, which should be ample, since it’s more than 3 times the estimated age of the universe. [/QUOTE] This won’t work. Suppose a meteorite fell that contained some rubidium-87 and some strontium-87; you could only use this to determine its age if you assumed that all the strontium was originally rubidium. Why should you assume that? ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [July 14, 2008, 12:58pm UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/7 "2008-07-14T12:58:06Z")
I’m going out on a limb here, but it is very likely that the only way to get strontium-87 is to have produced from rubinium-87 decay. Other isotopes of strontium may be present originally. OR – we have a pretty good idea of what mix of isotopes should be expected in a sample of strontium, and any excess strontium-87 can safely be assumed to be the result of the rubinium-87 decay. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 15, 2008, 4:56am UTC](https://boards.straightdope.com/t/can-scientists-determine-the-age-of-something-older-than-the-earth/456393/8 "2008-07-15T04:56:14Z")
[QUOTE=Alive At Both Ends] This won’t work. Suppose a meteorite fell that contained some rubidium-87 and some strontium-87; you could only use this to determine its age if you assumed that all the strontium was originally rubidium. Why should you assume that? [/QUOTE] Because there are several other isotopes of strontium. I assume it’s the ratio of strontium-87 to the other three isotopes that is used for age determination. From [here](http://en.wikipedia.org/wiki/Strontium) > [@](#): > > The alkali earth metal strontium has four stable, naturally occurring isotopes: 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.0%) and 88Sr (82.58%). Only 87Sr is radiogenic; it is produced by decay from the radioactive alkali metal 87Rb, which has a half-life of 4.88 × 1010 years. Thus, there are two sources of 87Sr in any material: that formed during primordial nucleo-synthesis along with 84Sr, 86Sr and 88Sr, as well as that formed by radioactive decay of 87Rb. I would assume that the older a sample is, the higher the ratio of 87Rb to the other isotopes.