The following is an extract from our monthly Launchpad newsletter, in which resident space expert Leah Crane journeys through the solar system and beyond. You can sign up for Launchpad for free聽here.
Let鈥檚 start at the beginning. For about a hundred million years after the big bang, there were no solids 鈥� no dust. First there was just boiling hot plasma, and then as it cooled, only hot gas. The universe went on expanding and that gas began to cool down and clump up, separating into globs like a broken buttercream. Over millions of years, the lumpiness got worse, eventually making pockets so dense that they collapsed in on themselves and began to fuse atoms together. These were the first stars.
They lived their entire lives in a dust-free universe, aside from small amounts that may have formed in their atmospheres. And then they exploded. In the immense heat and pressure of these first supernovae, heavy elements such as carbon and nickel formed 鈥� these became the first dust in the universe. And it immediately became important.
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While the first stars would have formed on their own from direct collapse, future generations tended to be born in stellar nurseries, which are huge clouds made up of mostly hydrogen and helium. When these collapse, they also heat up, creating radiation that pushes outward and counteracts the inward flow, bringing the clouds to a sort of uneasy equilibrium. That鈥檚 no good for star formation. Enter: dust. It also creates radiation from any heat it absorbs, but in this case it comes out in infrared wavelengths that pass right through the gas, instead of pushing back on the matter trying to collapse.
Once the stellar nursery has discharged its baby stars, dust plays an important role yet again: it is the main building block of planets. As young stars rotate, they collect a disc of dust and gas around them, and in a process somewhat similar to the one by which the first stars formed, clumps grow in that disc. These eventually stick together and become larger and larger rocks, and then planets. The composition of the dust in the disc has a powerful influence on the geochemistry of the resulting planets.
Even then, after helping with the formation of entire planetary systems, the role of cosmic dust isn鈥檛 over yet. Skip forward to just before the dawn of life on Earth, around 4 billion years ago. Things were violent in the early solar system, with many asteroids smashing and grinding together, producing more and more space dust. Hundreds of thousands of tonnes of that dust 鈥� or maybe even more than that, we don鈥檛 know for sure 鈥� blanketed the surface of the young Earth every year.
And the thing about cosmic dust is that it isn鈥檛 the same as dirt here on Earth. Some of the elements that are crucial to life, such as phosphorus and sulphur, are inaccessible in Earth dust but abundant in cosmic dust. I imagine you can see where I鈥檓 going with this. As all that cosmic dust fell on Earth, it would have brought with it ingredients that were crucial to the rise of life. For a long time, the possibility that space dust could have had anything to do with the first life on Earth was dismissed because the dust would have been spread all around the world in a layer too thin for any one location to have enough of those crucial elements to matter.
But thanks to a new study, that鈥檚 being rethought a bit. It turns out that in some locations, particularly on glaciers, cosmic dust could have gotten trapped in small pools of water, forming little cups of primordial soup. One of the ways we know this could happen is that such pools still exist in glacial regions today. In fact, they tend to be extremely radioactive because radiation fallout from around the world collects there, just like cosmic dust would have done billions of years ago. With a little burst of energy, such as a serendipitous lightning strike, those dusty pools could potentially have been the sources of the first life on our world.
From stars to planets to life itself, dust is important to it all. You might already be aware of the famous quote from Carl Sagan about star stuff, but I want to leave you with from astronomer Harlow Shapley: 鈥淲e are made of the same stuff as the stars, so when we study astronomy we are in a way only investigating our remote ancestry and our place in the universe of star stuff.鈥�
