[sandworm101]

They originate in space but do not necessarily come directly from space. Stuff is landing on earth all the time. Much of it then becomes dust/sand and gets moved around. What appears on a roof can be new falls from space, but also space stuff blown from elsewhere. Take a an amount of topsoil or sand. Run a magnet over it and you will find tiny flecks of space rock.

[jimhefferon]

I think finding such stuff is regarded by the author as cool. I don't remember the author saying so, but personally I would think finding it is cool whether it first landed on my neighbor's tree, or went straight to my roof.

[d1sxeyes]

But then by this logic isn’t everything made of space dust?

[defrost]

Some of the earth is made from space rocks; early planet forming and moon forming collisions, and later impact crater scale chunks.

Some of the earth is decayed earlier material - radon gas formed here on earth as a daughter product from uranium in granite.

Some of the earth has been created by man on earth in the atomic age ... all those extra elements tacked to the end of the periodic table.

[thaumasiotes]

> Some of the earth has been created by man on earth in the atomic age ... all those extra elements tacked to the end of the periodic table.

Don't those decay immediately? They would account for 0% of the earth.

[Keysh]

A significant amount of carbon-14 was added to the atmosphere from nuclear weapons testing. Since it has a half-life of about 5,000 years, most of it is still around. (The rest of it comes from cosmic rays smashing into atmospheric nitrogen.)

Granted, that's an isotope of a well-known element, not one of the "extra elements tacked to the end of the periodic table". I can point out that [tiny traces of plutonium-244 have been found in the ocean seafloor](https://www.npr.org/2021/05/13/996499035/freshly-made-pluton...). That has a half-life of about 80 million years; it's probably the result of ejecta from a supernova washing over the Earth several million years ago.

[defrost]

Not all of them .. and some of the material made in nuclear labs is new to earth and not sourced from space but identical to material that is.

There are a lot of isotopes.