1. Stardust (a/k/a "cosmic dust") is largely matter that didn't coalesce into planets or other celestial bodies during the formation of the solar system. A typical grain of stardust has a rock-like core and one or more outer layers of iced water, methane, or ammonia. Individual dust particles can be as small as a red blood cell or as large as a meter wide.
2. If you are far away from light pollution, you can probably see our solar system's stardust cloud without aid of a telescope. This is courtesy of a phenomenon called the Zodiacal light. Either before or after sunset (depending on the time of year and your position on Earth), sunlight radiating through Earth-centric stardust makes the dust particles sparkle against night sky.
3. In our solar system, stardust spirals into the shape of a disk, but not all star dust is confined to our solar system or to that shape. Four separate intergalactic dust clouds (a/k/a "nebulae") have been described in scientific literature. These are huge - perhaps 10-50 times the size of our sun. Eventually, they may collapse into each other and form new stars. Billions of years after that, those stars may go nova and form new dust.
4. The dust grains in nebulae are pretty scarce. A cubic kilometer of a cloud would probably hold only a few hundred to a few thousand miniscule grains. The remainder of the cloud would probably be made up of helium and hydrogen gas.
5. There's an old Joni Mitchell song that claims, "We are stardust" - and then almost right away equates stardust with "billion-year-old carbon." Was Ms. Mitchell speaking accurately?
6. She was, if we consider how much of our solar system's stardust settles to Earth. Estimates vary wildly between 5 and 300 tons per day. At least some of that dust has a carbon core, and all of that fallout undoubtedly integrates into dirt, where it feeds plants and, by extension, us. We are, indeed, at least partly carbon.
7. The enormous amount of carbon in human and animal bones is what helps scientists radiocarbon date the findings from ancient and prehistoric archeological sites.
8. Even though we know that all of Earth's plant and animal life is heavily carbon-based, a fundamental question remains. How did life itself begin on Earth? How did we humans become organisms that could inhale carbon dioxide and eat carbon-rich plants? According to Charles Darwin, the Old Testament got things all wrong. Life started not with countless plant and animal species being created in a few days' worth of Godly labor. Instead, sometime after Earth was formed, one or more inanimate cells somehow became animate. It was a chemical accident.
9. Eventually one or more animate cells multiplied. That, too, was an accident.
10. Also accidentally, some cellular progeny turned out to be only imperfect copies of their parents. When imperfections worked to a cell's advantage (or at least didn't kill the cell off), the cell passed its new peculiarities on to its progeny.
11. According to Darwin, eventually some single-celled creatures became multi-celled. Because not every multi-celled life form had the same idiosyncrasies, significant differences crept in. Over eons, plants and animals diverged into separate "kingdoms." As nature "rinsed and repeated," species emerged, thrived, and died out, and all the while new species formed.
12. We may not know as much as we'd like about specific timetables, but we do know that life on Earth began more than 3.5 billion years ago. That's the age of Earth's oldest fossils.
13. Was Darwin right in thinking that one or more inanimate cells spontaneously burst into life? Maybe not. Maybe they were alive from the start. Back in 1969, a carbon-rich meteorite fell to Earth in Murchison, Australia. An analysis in 2010 showed that it contained organic compounds. If such compounds routinely fell to Earth on meteorites or stardust, that might have seeded life on this planet.
14. The idea that life exists in the universe and is randomly distributed by stardust and meteorites is commonly referred to as "panspermia" (from Ancient Greek πᾶν (pan) 'all', and σπέρμα (sperma) 'seed'.) If indeed that is how life on Earth took hold, [drum roll, please...]
15. We are all space aliens.
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Added to Library on March 8, 2021. (727)
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