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Seeding Life on Earth: Cosmic Gifts, Ultimate Outsiders and Bringers of Light

In this episode, host Susan Mathews is in conversation with Dr. Craig Walton, a planetary scientist based at ETH Zürich and the University of Cambridge. Craig’s work spans the origins, evolution, and distribution of life in the Universe. In this podcast, we chat about cosmic dust, the origins of life on Earth, and phosphorus—a key element for life, known as the ‘bringer of the light of day’, and its more fiendish nickname, “The Devil’s Element”.

In a paper published in Nature Astronomy in February 2024, Craig and his colleagues note that life on Earth probably originated from “reservoirs of bio-essential elements” such as phosphorus, sulfur, nitrogen, and carbon. But our earth rocks are relatively poor in reactive and soluble forms of these elements. So where did they come from? Apart from meteorites and asteroids, they could have also found their way to earth through cosmic dust, mineral grain aggregates of less than 3 mm derived from asteroids and comets. And glaciers provide settings capable of both locally concentrating cosmic dust and initiating closed-system aqueous prebiotic chemistry in cryoconite holes, self-sustaining puddles or lakes.

In a more poetic turn, we talked about meteorites, which has been termed by Elizabeth Grosz as the ultimate outsider, a cosmological imponderable that might burst through the perceived limits of the known. Craig noted that these materials speak at a deeper level about where we come from and how we should live. Potentially, all life derives from these cosmic gifts. We are really made of stardust. Everything about meteorites and their eviscerated metallurgic intensity speaks to their incredible durability. And it’s a bit like us, right? There’s an unbroken genetic line between all of us here today to one pond, probably on the earth, four and a half billion years ago. It’s just absolutely crazy.

We then moved on to Craig’s PhD thesis on phosphorus, the backbone of DNA and our metabolism. It cycles through ecosystems in a mostly closed loop as organisms live, die and decay. This remarkable element, crucial for global food production, allows our civilization to flourish. However, with its overuse, we now face the dangers of fertilizer run-off such as algal blooms which can lead to ocean anoxic events which have been correlated with mass extinctions. For four and a half billion years, life has recycled minerals and resources, but we humans take them for granted. We churn through these resources, dump them in the oceans and move on. It can’t end well.

We ended our conversation with how phosphorus could guide us to life elsewhere in the universe. So far, the results indicate that we might be alone. But it could also be that we are the first on the scene, an elder species, which means we have a vast responsibility to figure out what we’re doing to each other, to the planet, and potentially to the whole galaxy.

More about our guest

Dr. Walton focused on the bio-essential element phosphorus (P) during his PhD at the University of Cambridge, UK. His project examined phosphorus in meteorites, the origins of life, and Earth’s crust over time. Now, Dr. Walton aims to apply this interdisciplinary scope to the broader (multi-element!) architecture of multiple problems surrounding Earth’s birth and subsequent evolution.

Outside of research, Craig writes science fiction as well as science communication articles on a wide range of topics.

If you want to hear more from Craig about all of the above, you can follow him on Twitter/X @lithologuy for updates.

Listen to our various podcasts

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In Season 2 of The Subverse, ‘water’ is our main theme. Join us as we explore the multifaceted dimensions of this life giving molecule.

In the third season of The Subverse, host Susan Mathews explores another elemental theme — fire. Join us for a series of thoughtful conversations, with experts in varied fields, centred around fire and the way it has influenced the world around us.

In Season 4 of The Subverse, host Susan Mathews explores the story of “earth”, an ancient element, a home to millions of lifeforms. Join us as we explore this pale blue dot in all its complexity.

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In season 2 of Arcx, our literary podcast mini-series, Anjali Alappat talks to eight South Asian sci-fi, fantasy, and speculative fiction writers about the stories that influenced and inspired them.

In this spin off of our podcast series, The Subverse, we uncover hidden and marginalized stories through a more personal storytelling lens