The elements that make up the bulk of the Earth were part of the presolar nebula. A similar (though not identical) mixture of elements is found in meteoritic material, which is thought to more accurately represent the mean abundances of that nebula (minus the volatiles) and indeed also agrees with the abundance patterns in the Sun.

There are grains of material trapped inside these meteorites that consist of solids that were already present in the presolar material. These are important because these grains were thought to have formed in individual stellar events and their isotopic compositions can be studied. These tell us that the Sun formed from material that has been inside many different stars of different types.

Stellar evolution and nucleosynthesis calculations tell us the same story. For example, whilst most of our oxygen was made in massive stars that underwent a core collapse supernova, such events do not produce much carbon. The C/O ratio tells us that most of our carbon comes via the winds from intermediate mass AGB stars. Heavy elements like Uranium are dominantly produced in supernovae, but others like Barium are not.

The details of how many generations have preceded the Sun and Earth has no single answer. Much of the solar hydrogen and helium could be pristine; some will have been through more than one star. Heavier elements (bar some lithium) will have been through at least one star. The fact that we have s-process elements like La and Ce, which are formed by neutron capture onto iron-peak elements, tells us those have been through at least two stars.

However, these are vast understimates. Mixing in the interstellar medium is reasonably effective. The material spewed out from supernovae and stellar winds 5-12 billion years ago has had plenty of time to mix throughout the Galaxy before the Sun's birth. Turbulence and shear instabilities should distribute material on galactic length scales in a billion years or less (Roy & Kunth 1995; de Avillez & Mac Low 2003), though local inhomogeneities associated with nearby recent events can persist over $10^{8}$ years. If this is the case, then the Sun is the product of the $\sim$ billion stars that died before it was born.

The elements that make up the bulk of the Earth were part of the presolar nebula. A similar (though not identical) mixture of elements is found in meteoritic material, which is thought to more accurately represent the mean abundances of that nebula (minus the volatiles) and indeed also agrees with the abundance patterns in the Sun.

There are grains of material trapped inside these meteorites that consist of solids that were already present in the presolar material. These are important because these grains were thought to have formed in individual stellar events and their isotopic compositions can be studied. These tell us that the Sun formed from material that has been inside many different stars of different types.

Stellar evolution and nucleosynthesis calculations tell us the same story. For example, whilst most of our oxygen was made in massive stars that underwent a core collapse supernova, such events do not produce much carbon. The C/O ratio tells us that most of our carbon comes via the winds from intermediate mass AGB stars. Heavy elements like Uranium are dominantly produced in supernovae (though current thinking is that merging neutron star binaries may be major contributors), but others like barium are not.

The details of how many generations have preceded the Sun and Earth has no single answer. Much of (perhaps 90%+) the solar hydrogen and helium could be pristine; some will have been through more than one star. Heavier elements (bar some lithium) will have been through at least one star. The fact that we have s-process elements like Ba, La and Ce, which are formed by neutron capture onto iron-peak elements, tells us those have been through at least two stars.

However, these are vast understimates. Mixing in the interstellar medium is reasonably effective. The material spewed out from supernovae and stellar winds 5-12 billion years ago has had plenty of time to mix throughout the Galaxy before the Sun's birth. Turbulence and shear instabilities should distribute material on galactic length scales in a billion years or less (Roy & Kunth 1995; de Avillez & Mac Low 2003), though local inhomogeneities associated with nearby recent events can persist over $10^{8}$ years. If this is the case, then the Sun is the product of the $\sim$ billion stars that died before it was born.

The elements that make up the bulk of the Earth were part of the presolar nebula. A similar (though not identical) mixture of elements is found in meteoritic material, which is thought to more accurately represent the mean abundances of that nebula (minus the volatiles) and indeed also agrees with the abundance patterns in the Sun.

There are grains of material trapped inside these meteorites that consist of solids that were already present in the presolar material. These are important because these grains were thought to have formed in individual stellar events and their isotopic compositions can be studied. These tell us that the Sun formed from material that has been inside many different stars of different types.

Stellar evolution and nucleosynthesis calculations tell us the same story. For example, whilst most of our oxygen was made in massive stars that underwent a core collapse supernova, such events do not produce much carbon. The C/O ratio tells us that most of our carbon comes via the winds from intermediate mass AGB stars. Heavy elements like Uranium are dominantly produced in supernovae, but others like Barium are not.

The details of how many generations have preceded the Sun and Earth has no single answer. Much of the solar hydrogen and helium could be pristine; some will have been through more than one star. Heavier elements (bar some lithium) will have been through at least one star. Mixing in the interstellar medium though means that the Sun was formed from material contributed from countless stellar deaths.

The elements that make up the bulk of the Earth were part of the presolar nebula. A similar (though not identical) mixture of elements is found in meteoritic material, which is thought to more accurately represent the mean abundances of that nebula (minus the volatiles) and indeed also agrees with the abundance patterns in the Sun.

There are grains of material trapped inside these meteorites that consist of solids that were already present in the presolar material. These are important because these grains were thought to have formed in individual stellar events and their isotopic compositions can be studied. These tell us that the Sun formed from material that has been inside many different stars of different types.

Stellar evolution and nucleosynthesis calculations tell us the same story. For example, whilst most of our oxygen was made in massive stars that underwent a core collapse supernova, such events do not produce much carbon. The C/O ratio tells us that most of our carbon comes via the winds from intermediate mass AGB stars. Heavy elements like Uranium are dominantly produced in supernovae, but others like Barium are not.

The details of how many generations have preceded the Sun and Earth has no single answer. Much of the solar hydrogen and helium could be pristine; some will have been through more than one star. Heavier elements (bar some lithium) will have been through at least one star. The fact that we have s-process elements like La and Ce, which are formed by neutron capture onto iron-peak elements, tells us those have been through at least two stars.

However, these are vast understimates. Mixing in the interstellar medium is reasonably effective. The material spewed out from supernovae and stellar winds 5-12 billion years ago has had plenty of time to mix throughout the Galaxy before the Sun's birth. Turbulence and shear instabilities should distribute material on galactic length scales in a billion years or less (Roy & Kunth 1995; de Avillez & Mac Low 2003), though local inhomogeneities associated with nearby recent events can persist over $10^{8}$ years. If this is the case, then the Sun is the product of the $\sim$ billion stars that died before it was born.