Dialogues with Claude

On panspermia, deep time, and the limits of what we can know

Article 3 of a series: Dialogues with Claude.ai

Before asking where the porphyrin ring came from, it is worth pausing to appreciate how many of life’s most consequential transitions it has been present for.

It was there in the earliest anaerobic prokaryotes, driving electron transfer in a world without oxygen. It was there when cyanobacteria developed chlorophyll-based photosynthesis and transformed the atmosphere — taking it from essentially no free oxygen to the roughly twenty-one percent we breathe today, a transformation that, as described in Article 1, destroyed almost all life then existing. It was there in the heme proteins that proved suited to managing the oxygen the atmosphere now contained. It was there when endosymbiosis brought a former bacterium inside the eukaryotic cell as the mitochondrion, and again when a cyanobacterium became the chloroplast — that second endosymbiosis deserving a moment’s pause, since the chloroplast is the reason plant life as we know it exists at all: every green leaf, every crop, every tree draws its energy from this captured cyanobacterium, still running the same photosynthetic chemistry it ran as a free-living organism billions of years ago.

Every major transition in the history of life passes through this molecule — through it in the sense that the porphyrin ring is not merely present at these transitions but is the molecular mechanism by which they operate. That fact is worth sitting with before we ask the next question: where did the porphyrin ring itself come from? And before that: where did the atoms that make it up come from? And before that: in what sense, if any, did life begin on Earth at all?

These questions do not have clean answers. What they have is a shape — and the shape is itself significant.

The Thread Runs Back Further Than Earth

In Article 2 we noted, as a closing flourish, that every atom in your body heavier than hydrogen was synthesized inside a star that no longer exists. It is worth dwelling on this more fully here, because it is not merely a poetic observation. It is the foundation of everything that follows.

A supernova remnant — the aftermath of a dying star. Every atom heavier than hydrogen in your body was forged in a stellar core and dispersed by an explosion like this one. The porphyrin thread begins here, not on Earth. (NASA)

The universe that emerged from the Big Bang contained essentially two elements: hydrogen and helium, with trace quantities of lithium. Everything else — carbon, nitrogen, oxygen, phosphorus, sulfur, iron, magnesium — was made later, inside stars, through nuclear fusion. A star is, among other things, an element factory. In its core, hydrogen fuses to helium, helium to carbon, carbon to heavier elements in sequence, each step releasing energy and building complexity. The chain ends at iron — the most stable nucleus, the point beyond which fusion no longer releases energy but requires it. A massive star that has built an iron core has reached the end of its fuel. It collapses, then explodes as a supernova — and in the violence of that explosion, elements heavier than iron are forged, and all of it, iron and everything above and below it, is scattered into space.

The iron at the center of the heme group in your hemoglobin was forged in a stellar core. The magnesium at the center of every chlorophyll molecule was forged in a stellar core. The carbon of the porphyrin ring itself was forged in a stellar core. These atoms drifted in interstellar space, were gathered by gravity into our early solar nebula, condensed into the early Earth, and eventually — through a chain of chemical and biological events we have been tracing across three articles — organized themselves into the molecules of life.

The porphyrin thread does not begin on Earth. It begins in stars. Which raises the question: at what point in this journey from stellar interior to living cell did the assembly of life’s precursor molecules begin? Was it only on Earth, in the prebiotic ocean? Or had chemistry already been at work, in space, for billions of years before the Earth existed?

What Arrives in Meteorites

The question is not purely speculative. We have physical evidence of what arrives from space.

On September 28, 1969, a meteorite fell near Murchison in Victoria, Australia. It was recovered quickly — within days — and has been studied intensively ever since. The Murchison meteorite is a carbonaceous chondrite: a class of meteorite rich in carbon-containing compounds, believed to be among the most primitive objects in the solar system, formed in our early solar nebula before the planets existed.

What it contained was extraordinary. Amino acids — more than ninety different kinds, including many found in living organisms and many not found in life on Earth. Nucleobases — the molecular components of DNA and RNA. Sugar molecules. And porphyrin-like compounds: molecules structurally related to the porphyrin ring at the heart of chlorophyll and heme.

These are not contaminants. The amino acids in the Murchison meteorite include molecules that come in mirror-image forms — left-handed and right-handed versions. This property is called chirality. Life on Earth uses almost exclusively left-handed amino acids — a choice made, by whatever mechanism, at the very origin of life, and maintained without exception across every living organism since. The meteorite contains both forms in roughly equal proportions, which is exactly what abiotic chemistry produces and exactly what contamination from terrestrial biology would not produce. The organic molecules in the Murchison meteorite were made in space, before the Earth existed.

Life’s raw materials are not rare. They are, in a sense, cosmic.

IMAGE: Murchison meteorite — Wikimedia Commons

The Murchison meteorite, which fell in Victoria, Australia in 1969, contained more than ninety amino acids and porphyrin-like compounds — evidence that the chemical precursors of life are products of ordinary chemistry operating in space, before Earth existed.

This does not prove that life began in space. It proves that the chemical precursors of life — including precursors of the porphyrin ring — are products of ordinary chemistry operating in the interstellar medium and in the early solar nebula.

Panspermia: The Serious Case

The hypothesis that life’s precursors, or life itself, arrived on Earth from elsewhere is called panspermia — from the Greek for ‘seeds everywhere.’ It is not a fringe idea. It has been entertained by working researchers for more than a century, and the evidence from meteorites has made it increasingly credible, though as yet unconfirmed.

The astronomer Fred Hoyle — whose science fiction and popular science writing I read with pleasure as a teenager, and who introduced many of us to the strangeness of the cosmos — developed, with his colleague Chandra Wickramasinghe, a specific and detailed version of panspermia. They argued that interstellar dust clouds contain complex organic molecules, including the precursors of biological polymers, and that these molecules seed planetary surfaces throughout the galaxy. Hoyle held some positions that proved incorrect and some that remain contested — but his panspermia work, and the evidence for complex organics in interstellar space that has accumulated since, deserves to be evaluated on its own merits.

The Hoyle-Wickramasinghe proposal goes further than most researchers are currently prepared to follow: they argued not merely that organic precursors arrived from space but that intact microorganisms, or their remnants, may have done so. This version remains unconfirmed and controversial. The weaker version — that organic chemistry was already far advanced in space before it reached Earth — is supported by the meteorite evidence and taken seriously by researchers in the field.

A related and more specific hypothesis is lithopanspermia: the transfer of microbial life between planets inside rocks ejected by asteroid or comet impacts. Mars and Earth have been exchanging material throughout their histories — Martian meteorites have been found on Earth, and Earth rocks have certainly reached Mars, propelled by the violence of large impacts and carried across space by the solar wind and gravitational dynamics. If life existed on Mars in its early, wetter period, it could in principle have arrived here. If life arose on Earth first, it could in principle have seeded Mars.

Francis Crick — co-discoverer of the structure of DNA — and Leslie Orgel proposed a still more specific variant: directed panspermia, the deliberate seeding of Earth by an intelligent civilization elsewhere in the galaxy. Crick and Orgel were not asserting this as fact. They were pointing out that it could not, at that stage, be ruled out — and that the universality of the genetic code, the same in every living organism on Earth, is exactly what we would expect if all terrestrial life descended from a single introduced population. They held the idea open as a possibility worth taking seriously rather than dismissing.

The Dissolving Boundary

Panspermia, in any of its forms, reframes the question of life’s origin. Instead of asking ‘when did life begin on Earth?’ it asks ‘at what stage of assembly did the material arrive?’ — as atoms, as simple organic molecules, as complex polymers, as self-replicating systems, or as something we would recognize as alive?

But the more carefully we examine that question, the harder it becomes to answer — not because the evidence is insufficient, but because the boundary between living and non-living chemistry may not be where we habitually draw it.

Consider what life requires at its most minimal: a molecule that can copy itself, using raw materials from its environment, with sufficient fidelity to pass information to the next generation but sufficient error to allow variation. That is the bare minimum for natural selection to operate. Everything else — cell membranes, metabolism, protein synthesis — is elaboration built on that foundation.

DNA carries the genetic instructions for all known life, encoded in sequences of four chemical bases. RNA is a related but older molecule — older in the sense that it appears to have preceded DNA in the history of life — that can both carry genetic information and catalyze chemical reactions, including, crucially, reactions involved in its own replication. This dual capacity makes RNA the leading candidate for the earliest self-replicating chemistry. The ‘RNA world’ hypothesis proposes that the earliest life was based on self-replicating RNA molecules, before DNA took over the information-storage role and proteins took over most of the catalytic role. RNA molecules with catalytic activity — called ribozymes — have been found in living cells, ancient remnants of this earlier era.

[ IMAGE: Model of DNA double helix — Wikimedia Commons]

DNA carries the genetic instructions for all known life. RNA, its molecular cousin, can both store information and catalyze chemical reactions — including, in some molecules, reactions involved in its own replication. This dual capacity makes RNA the leading candidate for the earliest self-replicating chemistry on Earth, and possibly elsewhere.

But RNA itself is a complex molecule that requires precursors. Those precursors require their own precursors. At each step backward in the chain, the molecules become simpler and more plausibly the products of abiotic chemistry — chemistry that requires no life to produce it. The porphyrin ring, as we have noted, forms spontaneously. Amino acids form spontaneously. Nucleobases — the components of RNA and DNA — form spontaneously and have been found in meteorites.

Where, in this chain from simple abiotic chemistry to self-replicating RNA to the first cell, does non-life end and life begin? No one knows — and the more carefully researchers examine the question, the less clear it becomes that there is a sharp boundary to find. What we call ‘life’ may be a region on a continuum of increasing chemical complexity and self-organization, not a threshold crossed at a definable moment.

This is exactly the pattern the series has traced at every other boundary we have examined: between plant and animal, between individual and community, between mechanism and mind. In each case, what appeared to be a wall turned out, on close inspection, to be a gradient. The boundary between life and non-life appears to be no different.

What Most of the Universe Is Made Of — And What We Do Not Know

The story we have been telling — from stellar nucleosynthesis through prebiotic chemistry to the first cells — involves only ordinary matter: atoms, molecules, the stuff of chemistry and biology. But ordinary matter — everything made of atoms — constitutes only approximately five percent of the total energy content of the universe.

The remaining ninety-five percent consists of dark matter (roughly twenty-seven percent) and dark energy (roughly sixty-eight percent), neither of which has been directly detected or characterized at the level of its intrinsic nature. Dark matter is inferred from its gravitational effects on galaxies and galaxy clusters — it must be there, because without it the observed structures could not hold together. Dark energy is inferred from the observed acceleration of the universe’s expansion — something must be driving it, and whatever that something is, it constitutes most of what the universe contains.

We do not know what dark matter is made of. We do not know what dark energy is. We know their effects but not their nature.

This bears on everything the series has discussed. The view that dismisses mind as an anomaly — a late and accidental product of matter, fully explicable by the mechanisms of neuroscience — is a view about five percent of the universe. What the other ninety-five percent is, from the inside, is entirely open. Bohm’s implicate order — the deeper level of reality from which both matter and mind unfold — need not be confined to the five percent we can observe. It may be a property of the whole.

The Periodic Table and the Pattern That Precedes the Instance

There is one further observation about the structure of matter that belongs in this article, because it illuminates what ‘pattern preceding instance’ actually looks like in practice.

In 1869, Dmitri Mendeleyev arranged the known elements in a table ordered by atomic weight and noticed that chemical properties recurred at regular intervals. He had sixty-three elements. The table his arrangement produced had gaps — positions where an element should exist, based on the pattern, but none had been found. Mendeleyev predicted the missing elements and described their properties in detail before they were discovered. When gallium was found in 1875 and germanium in 1886, their properties matched his predictions closely. The pattern had preceded the instances.

The quantum mechanical model of the atom, developed in the twentieth century, explained why the periodic table has the structure it does: electron shell configurations determine chemical properties, and the mathematics of quantum mechanics dictates the possible configurations. The table’s shape is not an empirical accident. It is a consequence of deep mathematical structure — a structure that was there before any of the elements were known, before any atom existed, arguably before the universe began.

Contemporary research extends this further. Theoretical physicists predict the existence of an ‘island of stability’ among superheavy elements — a region around elements 114 to 126 where certain combinations of protons and neutrons may produce nuclei more stable than their neighbors. Some of these elements have been synthesized and their stability measured. The predictions have held with reasonable accuracy. The pattern preceded the instances.

On Bohm’s account, this is exactly what we should expect. The implicate order is mathematical in character — the patterns we discover in nature are not imposed on matter from outside but are expressions of a deeper structure that matter inherently carries. The periodic table is one of the clearest cases: a pattern so deeply enfolded in the nature of matter that it could be glimpsed from sixty-three examples and used to predict what the remaining elements would be like.

The porphyrin ring is another such case. Its fitness for electron transfer, for light capture, for oxygen management — all enfolded in its molecular architecture, expressing themselves as conditions allowed. The star that forged the iron at the center of your heme group did not know it was making a component of hemoglobin. The prebiotic chemistry that assembled the first porphyrin ring did not know it was making the scaffold that would underlie both photosynthesis and respiration. But the potential was there, in the structure of the molecule, waiting for conditions that would allow it to unfold.

The Shape of What We Cannot Know

We began this series with a question about two molecules and ended three articles later at the edge of cosmology, the origin of life, and the intrinsic nature of most of the universe. Along the way, every boundary we examined dissolved: between plant and animal, between self and other, between individual and community, between mechanism and mind, between life and non-life. In each case, what appeared to be a wall turned out to be a gradient.

What we cannot know, given the state of the evidence, is at least as significant as what we can. The rock record of the first billion years of Earth’s history is largely destroyed. The question of whether life’s precursors arrived from space is unresolved. The question of whether the boundary between chemistry and biology is a real boundary or a useful fiction remains open. The nature of dark matter and dark energy is unknown. Whether the universe’s mathematical structure reflects a deeper implicate order is a serious philosophical proposal, not yet a confirmed physical theory.

And yet these gaps are not random. They form a pattern. Every gap in our knowledge points toward the same territory: the intrinsic nature of things, as opposed to their relational structure; the inside of matter, as opposed to its observable behavior; the ground from which both life and mind unfold, whatever that ground may be.

The Higgs boson was predicted decades before it was detected — its existence was inferred from the internal consistency of the Standard Model of particle physics. The prediction proved correct. We cannot run the same experiment on the origin of life or the first porphyrin ring — the evidence is destroyed, the conditions unrepeatable, the timescales inaccessible. But the network of inferences we have assembled across these three articles hangs together with a coherence that is itself worth noting.

A random collection of guesses would not hang together this way.

The porphyrin ring arrived — from stellar nucleosynthesis, through interstellar chemistry, possibly through meteorite delivery, certainly through prebiotic chemistry — and was incorporated into the first life, and has not left since. It is present now in the mitochondria of every cell in my body, and in the chloroplasts of the avocado plant sitting for years beside my front room window. The same ring, the same biosynthetic pathway, unbroken across four billion years and two different kingdoms of life, connecting the inside of a dead star to the inside of a living cell.

Whether the universe that produced this was, in some sense, always tending toward it — whether the pattern was enfolded before the instances existed — is the question the series has been circling. It is not a question science can currently answer. It is a question that the evidence does not foreclose.

The articles in this series have now traced the porphyrin thread from prebiotic chemistry to the philosophy of mind to the edge of cosmology. The questions that remain — about free will and agency, about what a long inquiry reveals about what we do not know — are the subject of the articles to come.

Ron Pavellas

Stockholm, 2026