3 ms·

What exactly does 4.6B-year-old mean? Landed on the Earth 4.6B years ago? That doesn't sound right, the Earth isn't that old. Flew off its former body 4.6B ye

by dheera 5y ago

What exactly does 4.6B-year-old mean? Landed on the Earth 4.6B years ago? That doesn't sound right, the Earth isn't that old. Flew off its former body 4.6B years ago? How do we measure that? Created 4.6B years ago? How does one define created, considering everything was ultimately created during the big bang?

ardit33 5y ago
Created by clumped dust 4.6b years ago when the solar system was being formed.... but it hasn't been part of a larger body, so it is not that compressed, so it is not a chunk of another larger body that split off from collisions. It contains organic material, which means the dust that formed our solar system, contained plenty of it. If it arrived yesterday in earth, it still is 4.6b old. "Identifying organic compounds would support the idea that early meteorites carried amino acids – the building blocks of life – to supply the Earth’s primordial soup where life first began. “Carbonaceous chondrites contain organic compounds including amino acids, which are found in all living things,” said Director of Astrochemistry at EAARO Derek Robson who found the meteorite and who will soon join Loughborough University as an academic visitor for collaborative research. “Being able to identify and confirm the presence of such compounds from a material that existed before the Earth was born would be an important step towards understanding how life began.”"
- ars 5y ago
  > but it hasn't been part of a larger body, so it is not that compressed, so it is not a chunk of another larger body that split off from collisions. It's way too small to clump from its own gravity, it pretty much has to be a portion of something MUCH larger.
  - dredmorbius 5y ago
    That assertion gets into questions of asteroid formation, which I find fascinating, though there's very little information I've been able to find. Keep in mind that "gravitational accretion" simply kicks the can a bit further: the chunks that accrete gravitationally must themselves form and congeal somehow. What I understand of solar system formation is that all "metallic" solar systems (though with a substantial portion of elements other than hydrogen) from from the remains of earlier stars. So you have a nova, supernova, stellar collapse, collision (stars, white dwarves, neutron stars, ...). This ejects heavy materials (principally H, He, C, O, N, though others --- water is probably the most common non-elemental molecule in the Universe), and also creates pressure waves and imparts angular momentum. Both factors can draw material together. There's also probably a lot of plasma in the mix, so that different portions of the cloud carry different charges. These may be attracted, repelled, and spark discharges (which might themselves melt and fuse material). There may also be surface-tension effects and other factors at play. Somehow, clumps form. Gravity is a force at work, but not the only force. Disclaimer: not an astronomer, just interested in far too many divers subjects. If anyone has anything authoritative to say on this I'm all ears. Most references I can find are either extremely basic, or address the formation of asteroid belts but not the objects within them. There's some hypothesis on formation (condensation, shock waves, jet flows) here: http://www.psrd.hawaii.edu/Sept02/isotopicAges.html http://www.psrd.hawaii.edu/Sept02/isotopicAges.html
dredmorbius 5y ago
It's the time since the rock itself fused from molten or other non-fixed form. The age of formation of rock is typically determined unequivocably by radiometric dating. That "clock" uses the ratios of long-lived radioactive elements and their decay products (this is not radio carbon dating, which is similar but effective over a much shorter timespan of about 50,000 years). The radiometric clock starts when the materials in the sample solidify and initial proportions of mother and daughter elements are fixed, "neither the parent nuclide nor the daughter product can enter or leave the material after its formation" (Wikipedia). That point in time is the "age" of the rock. The specific decay chains used in geology are uranium–lead, samarium–neodymium, potassium–argon, rubidium–strontium, and uranium–thorium. These may rely on crystaline structures which cannot form when the daughter elements (decay products) are present, therefor the amount of daughter element present gives the age. (I know this is the case for some methods, I'm unsure it applies to all. The "this structure cannot form when the daughter products are present" feature is a compelling argument for age.) https://en.wikipedia.org/wiki/Radiometric_dating https://en.wikipedia.org/wiki/Radiometric_dating Newly-formed lava or other molten materials are "new" --- they've just been created as rock. The elements within them are older --- those date to whatever radiological apocalypse formed them (stellar fusion for elements up to iron, various novae and collisions between white dwarves and neutron stars for elements heavier than iron). And of course the protons and neutrons comprising them ... mostly ... date to the origin of the Universe in the Big Bang (there is some spontaneous creation of particles due to quantum energy and mass-energy fluctuations, though that's minimal). The atomic transmutation of elements gives some interesting results. Virtually all of the helium in the Universe formed in stars from fusion of hydrogen. A very small percentage was formed in the Big Bang. But virtually all helium on Earth is the result of radioactive decay of heavy elements, forming beta particles (two protons and two neutrons), that is, a helium nucleus. When that picks up electrons, it becomes helium. It's generally trapped with natural gas and produced as a by-product of gas wells.
Koshkin 5y ago
I mean, probably in the same way as one would define, say, a person's age and the time of "creation". (Individual atoms are, of course, much older than any the object that is built from them, but that does not matter.)

by dheera 5y ago

ardit33 5y ago

Created by clumped dust 4.6b years ago when the solar system was being formed.... but it hasn't been part of a larger body, so it is not that compressed, so it is not a chunk of another larger body that split off from collisions. It contains organic material, which means the dust that formed our solar system, contained plenty of it. If it arrived yesterday in earth, it still is 4.6b old. "Identifying organic compounds would support the idea that early meteorites carried amino acids – the building blocks of life – to supply the Earth’s primordial soup where life first began. “Carbonaceous chondrites contain organic compounds including amino acids, which are found in all living things,” said Director of Astrochemistry at EAARO Derek Robson who found the meteorite and who will soon join Loughborough University as an academic visitor for collaborative research. “Being able to identify and confirm the presence of such compounds from a material that existed before the Earth was born would be an important step towards understanding how life began.”"

ars 5y ago
> but it hasn't been part of a larger body, so it is not that compressed, so it is not a chunk of another larger body that split off from collisions. It's way too small to clump from its own gravity, it pretty much has to be a portion of something MUCH larger.
- dredmorbius 5y ago
  That assertion gets into questions of asteroid formation, which I find fascinating, though there's very little information I've been able to find. Keep in mind that "gravitational accretion" simply kicks the can a bit further: the chunks that accrete gravitationally must themselves form and congeal somehow. What I understand of solar system formation is that all "metallic" solar systems (though with a substantial portion of elements other than hydrogen) from from the remains of earlier stars. So you have a nova, supernova, stellar collapse, collision (stars, white dwarves, neutron stars, ...). This ejects heavy materials (principally H, He, C, O, N, though others --- water is probably the most common non-elemental molecule in the Universe), and also creates pressure waves and imparts angular momentum. Both factors can draw material together. There's also probably a lot of plasma in the mix, so that different portions of the cloud carry different charges. These may be attracted, repelled, and spark discharges (which might themselves melt and fuse material). There may also be surface-tension effects and other factors at play. Somehow, clumps form. Gravity is a force at work, but not the only force. Disclaimer: not an astronomer, just interested in far too many divers subjects. If anyone has anything authoritative to say on this I'm all ears. Most references I can find are either extremely basic, or address the formation of asteroid belts but not the objects within them. There's some hypothesis on formation (condensation, shock waves, jet flows) here: http://www.psrd.hawaii.edu/Sept02/isotopicAges.html http://www.psrd.hawaii.edu/Sept02/isotopicAges.html

dredmorbius 5y ago

It's the time since the rock itself fused from molten or other non-fixed form. The age of formation of rock is typically determined unequivocably by radiometric dating. That "clock" uses the ratios of long-lived radioactive elements and their decay products (this is not radio carbon dating, which is similar but effective over a much shorter timespan of about 50,000 years). The radiometric clock starts when the materials in the sample solidify and initial proportions of mother and daughter elements are fixed, "neither the parent nuclide nor the daughter product can enter or leave the material after its formation" (Wikipedia). That point in time is the "age" of the rock. The specific decay chains used in geology are uranium–lead, samarium–neodymium, potassium–argon, rubidium–strontium, and uranium–thorium. These may rely on crystaline structures which cannot form when the daughter elements (decay products) are present, therefor the amount of daughter element present gives the age. (I know this is the case for some methods, I'm unsure it applies to all. The "this structure cannot form when the daughter products are present" feature is a compelling argument for age.) https://en.wikipedia.org/wiki/Radiometric_dating https://en.wikipedia.org/wiki/Radiometric_dating Newly-formed lava or other molten materials are "new" --- they've just been created as rock. The elements within them are older --- those date to whatever radiological apocalypse formed them (stellar fusion for elements up to iron, various novae and collisions between white dwarves and neutron stars for elements heavier than iron). And of course the protons and neutrons comprising them ... mostly ... date to the origin of the Universe in the Big Bang (there is some spontaneous creation of particles due to quantum energy and mass-energy fluctuations, though that's minimal). The atomic transmutation of elements gives some interesting results. Virtually all of the helium in the Universe formed in stars from fusion of hydrogen. A very small percentage was formed in the Big Bang. But virtually all helium on Earth is the result of radioactive decay of heavy elements, forming beta particles (two protons and two neutrons), that is, a helium nucleus. When that picks up electrons, it becomes helium. It's generally trapped with natural gas and produced as a by-product of gas wells.

Koshkin 5y ago

I mean, probably in the same way as one would define, say, a person's age and the time of "creation". (Individual atoms are, of course, much older than any the object that is built from them, but that does not matter.)