3
$\begingroup$

This is a follow up question asked and answered (Radio-dating and the age of the earth)

The answer was given that the mineral Zircon is formed under high pressures and temperatures. How do we know, for example, most of the Zircon on Earth wasn't formed in some extraterrestrial event before the Earth formed?

$\endgroup$
1
  • $\begingroup$ Have you and details, or is the Question purely speculative? $\endgroup$ Dec 2, 2023 at 21:36

2 Answers 2

13
$\begingroup$

It would seem strange to find that the oldest material found on Earth all formed in some extraterrestrial event that post-dates the ages of the oldest meteoritic material in the Solar System.

The Solar System is dated using the oldest solid material that can be found in ancient meteorites. This is dated using various techniques, not just the U-Pb decay chain (e.g. Rb-Sr; Sm-Nd). These ages all converge on an age for the Solar System of around 4.56-4.57 billion years since the first solids formed.

The oldest materials and minerals found on Earth are younger than this (the oldest zircons found yet are about 4.4 billion years old - Wilde et al. 2001), because the Earth solidified somewhat later. The hot formation of the Earth would have reset the clock on any materials incorporated into it at that time (see the same reference).

I can't see what event it could be that you propose enriched the Earth with zircon (note that zirconium is an element) but left no trace in the material that formed meteorites.

Edit: To address a possible point of confusion; the radioactive dating method tells you how long it is since the zircon mineral was formed, not how old the atoms of the chemical element zirconium are. All the atoms of zirconium were formed inside other stars by nuclear processes before the Solar System formed.

$\endgroup$
9
  • $\begingroup$ "These ages all converge on an age for the Solar System of around 4.56-4.57 billion years since the first solids formed." -- Did you mean to write "..., when the first solids formed"? $\endgroup$ Dec 1, 2023 at 20:53
  • $\begingroup$ Zircon is more heat-resistant than some igneous rocks. That makes it theoretically possible for meteoritic zircon crystals to be incorporated into the still-molten Earth. $\endgroup$
    – Mark
    Dec 1, 2023 at 21:56
  • $\begingroup$ @Mark do you have a reference for any Earth-based zircon older than 4.4 billion years old? Whereas all primitive meteoritic samples are older than this. $\endgroup$
    – ProfRob
    Dec 1, 2023 at 22:21
  • $\begingroup$ Thanks for the thoughtful answers on possibly a dumb question of mine. I suppose I want to know how we don't know, for example, that all the material that makes up our solar system wasn't a conglomerate of matter created 4.5 billion years ago by some event and then our solar system was formed (@WayneConrad). Could 4.5 billion year old zircon have survived a younger earth's formation without 'resetting' (@ProfRob) $\endgroup$
    – Lucas
    Dec 2, 2023 at 8:54
  • 1
    $\begingroup$ @WayneConrad No, they meant to say the current age is 4.56-4.57 billion years since the first solids formed. The solar system was not (or at least is not thought to have been) already 4.56-4.57 billion years old at that time. $\endgroup$
    – user253751
    Dec 2, 2023 at 13:05
8
$\begingroup$

Zirconium is an element, thought to be the product of the S-process in asymptotic giant branch stars.

Zircon is a mineral, zirconium silicate, used in geological dating. Crystals of zircon form at high temperatures and pressures.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.