Radioactive dating??

[Donkeiller]

My understanding is that the age of the Solar system is determined by Uranium/lead radioactive decay dating But this presumes the the Uranium "clock" started ticking some 4.65 billion years ago.

Now heavy elements, such as uranium, are only produced in Type II supernovas. Yet the solar system was formed by the collapse of a gas-cloud.

Are we to believe that all the uranium in the Solar System was produced by a nearby supernova that "seeded" the gas cloud?

What about uranium from earlier supernovas "contaminating" the clould?

Or is this taken into account?

[Uranium235]

Our Sun is a third generation star, and therefore the solar system contains traces of heavier elements that were produced from the previous two supernovae. Or at least thats how the theory goes...

[Donkeiller]

Our Sun is a third generation star, and therefore the solar system contains traces of heavier elements that were produced from the previous two supernovae. Or at least thats how the theory goes...

Thanks, that is what I thought. There must have been 100s of supernovas contributing to the heavy elements on our Solar system.

So how come they can use the Uranium-Lead decay series as a clock? Given that there will be many different- and unknowable, start times?

[Uranium235]

Thanks, that is what I thought. There must have been 100s of supernovas contributing to the heavy elements on our Solar system.

So how come they can use the Uranium-Lead decay series as a clock? Given that there will be many different- and unknowable, start times?

That may be a question for the Phyisics and space science sub forum, there are a better qualified personnel down there to help with your question than I am

But I doubt there would have been hundreds if the current given age of the universe is accurate(ish), there simply wouldnt have been enough time for that many. More likely is that the previous two generations could have been very large, very hot stars... big enough to seed the elements we have when they went pop. 

[Owmuchonomy]

I'm no expert but my understanding of this is as follows from my Coursera course currently underway.  The 'start of the clock' as you describe it can easily be pinned down in the solar system by looking at a substance called Zircon, either from earth or the moon or even meteorites.  The moon rocks by the way are slightly older than earth's.  Zircon when it forms binds Uranium but not lead.  So when Zircon first forms and solidifies it traps any Uranium around but not Lead. Its then possible to work out the 'new' Lead content in the Zircon, because it must have come from the Uranium when the rock first formed and calculate the age of the rock from the half life of Uranium.  To improve accuracy measurements are taken from different isotopes of Uranium and where the data correlates gives you your answer, about 4.56 Billion years for our Solar System.

[Knight of Clear Skies]

As Owmuchonomy says above, zircons are the gold standard for radiometric dating. It's hard to conceive of a better time marker, as the chemistry of their formation rejects contaminants and there are two separate decay chains to check against each other.

Dating rocks gives the time at which they formed not the age of the materials they formed from. The decay chains occur within a sealed crystal which retain both a sample of the original material and any decay products. Most rocks on Earth are much younger than the solar system as plate tectonics melts and recycles old rocks into new ones, mixing the products of radioactive decay.  

[symesie04]

Our Sun is a third generation star, and therefore the solar system contains traces of heavier elements that were produced from the previous two supernovae. Or at least thats how the theory goes...

Is "generation" a correct term? If so then i have no idea why both "generation" and "population" (in reverse) are attributed to stars. The Sun is definitely a Population 1 star.

[Knight of Clear Skies]

Stellar populations are another of those confusing astronomical terms. Often this kind of thing happens because objects are identified or grouped together before it's properly understood what they are. Think of asteroid (means star-like), planetary nebula etc.

[symesie04]

So does that mean both Generation 3 and Population 1 are both legitimate terms for the Sun?

[Knight of Clear Skies]

Edit - sorry, wrong thread.

[Uranium235]

symesie04, on 28 Jan 2015 - 11:23 AM, said:

Is "generation" a correct term? If so then i have no idea why both "generation" and "population" (in reverse) are attributed to stars. The Sun is definitely a Population 1 star.

Done a bit of reading and "population" seems to refer to the metal content of stars, with 1 being young and metal rich, and 2 being older and having less metal. Whereas "generation" refers to exactly that (ie: did it have parent or grandparent star). Seems logical to me  so by that definition - yes, the Sun is a 3rd Gen and P1 star (unless somebody can correct me!).

[Owmuchonomy]

Hello me again. guess what this week's Coursera topic is? Anyway Uranium235 is close enough. Population is the usual definition and our sun as rightly pointed out is a population 1 star now defined as metal rich. Population was defined differently some time ago and referred to normal motion versus peculiar motion or population 2 stars. Population 2 stars appear in globular clusters frequently and are metal scarce stars. Population 3 stars are thought to have existed in the past as Hydrogen/Helium only stars but as far as I know are not observable now. So our sun 'grew up' from past star forming areas hence the relatively high metal content. As far as I can tell the term generation is loosely used in similar form as Uranium235 said based where the star came from.

[ollypenrice]

The 'population' nomenclature was Walter Baade's. For a really great biography of the astronomer's astronomer of the 20th century, try http://press.princeton.edu/titles/7186.html

It's a great read about a great man. Not as flashy as Hubble, not as lucky, not as self-publicising but, in my view, even better.

Olly

[Christopher Davenport]

Interesting read, not what I thought it would be when I first saw the title.

Found a interesting read on this.

http://www.universetoday.com/15575/how-old-is-the-solar-system/

[Carina Lass]

From the title I thougt you were going out with a Girl from Chernobyl.

From what I gather from science and stuff.... the last to be produced uranium is easier to see than the older stuff which is already down to a lower level.

As in the highest levels are what is measured rather than the overall background.

Not sure how they do that, but that's how I understand it.