The Narrative's Key Figures

In 1979, Italian publisher Mondadori released "La Nuvola della Vita," authored by Fred Hoyle and Chandra Wickramasinghe. I eagerly devoured this book, as it promised insights into significant cosmological questions that have long captivated my attention. This work was a translation of the previous year's publication by Dent, titled "Life Cloud: The Origin of Life in the Universe," which served as a foundational text for the panspermia theory advocated by the authors.

Reflecting on Hoyle and Wickramasinghe's book recently, I came across a 2018 study published in Progress in Biophysics and Molecular Biology, which revisits the panspermia hypothesis. Titled "Cause of Cambrian Explosion — Terrestrial or Cosmic?", this article synthesizes contemporary scientific findings, including investigations into the Polonnaruwa meteorite that fell in Sri Lanka in late 2012. Although Fred Hoyle passed away in 2001, his longtime collaborator, Chandra Wickramasinghe, continues to contribute to this ongoing discourse.

Born in England in 1915, Hoyle was pivotal in developing the understanding of nucleosynthesis for elements heavier than helium, a process occurring within stars at extreme temperatures. His groundbreaking idea of concentric layers of increasingly heavier elements remains a vital part of modern astrophysics, particularly in the context of supernova explosions.

Hoyle's name is also entwined with the Big Bang theory, a term he coined during a 1949 BBC radio broadcast, albeit with a tone of irony as he was a proponent of the steady-state theory, which posits the continuous creation of matter.

Chandra Wickramasinghe, born in 1939 in Colombo, Sri Lanka, is recognized as a mathematician, astronomer, and astrobiologist. After studying under Hoyle at Cambridge, he became a professor at University College of Cardiff, publishing numerous works aimed at popularizing the panspermia hypothesis along with over 350 scientific articles, many featured in Nature.

While science is fundamentally about evidence rather than eminent names, it’s noteworthy that both abiogenesis and panspermia lack definitive proof. Therefore, it’s intriguing to explore the reasoning and circumstantial evidence that support the panspermia hypothesis, particularly given the unwavering support of distinguished scientists like Hoyle and Wickramasinghe for a theory often dismissed by their peers.

This article aims to outline the obscure theoretical framework underpinning the panspermia hypothesis, a narrative filled with eccentric concepts and contentious theories, yet driven by a surprisingly profound cosmic perspective that captivates the imagination.

An Astonishingly Low Probability

The widely accepted theory of abiogenesis posits that life originated on Earth from inorganic materials through a gradual process of chance, likely occurring in hydrothermal vents—submerged volcanic fissures that release heated water rich in sulfur and other minerals.

Hoyle and Wickramasinghe’s (H and W) critical stance on abiogenesis argues that the complexity of life is too profound to suggest that it could have arisen purely through random processes starting from inorganic matter.

In their 1981 work "Evolution from Space," they vocally challenged the then-dominant "primordial soup" hypothesis, which gained traction from a landmark experiment by Stanley Miller and Harold Urey in the 1950s. This experiment simulated early Earth conditions, leading to the unexpected formation of various amino acids—building blocks of life.

However, amino acids are merely precursors; they do not constitute life itself. H and W highlighted the extreme improbability that essential macromolecules such as enzymes could have formed from amino acids through random trials.

Enzymes, which are long chains of proteins that act as catalysts in biological processes, are crucial for metabolism. H and W estimated that the chance of assembling a fully functional enzyme by random means is exceedingly low—approximately 1 in 10²?, or 1 in 100 billion billions.

They further assessed the probabilities concerning the total number of known enzymes:

By itself, this small probability could be faced, because one must contemplate not just a single shot at obtaining the enzyme, but a very large number of trials such as are supposed to have occurred in an organic soup early in the history of the Earth. The trouble is that there are about two thousand enzymes, and the chance of obtaining them all in a random trial is only one part in (10²?)²??? = 10?????, an outrageously small probability that could not be faced even if the whole universe consisted of organic soup. [F. Hoyle, N.C. Wickramasinghe, “Evolution from Space. A theory of cosmic creationism”, 1981]

The odds of achieving a successful outcome against an overwhelming number of unfavorable combinations—1 followed by 40,000 zeros—is astoundingly low, especially when considering the limited geological time available for life to transition from inorganic materials to self-replicating organisms.

The original abiogenesis hypothesis suggested that the incubation period for life in the primordial seas was several hundred million years. However, recent findings suggest a much shorter timeframe. Until recently, the oldest confirmed evidence of microbial life consisted of fossilized cyanobacteria dating back 3.5 billion years, leaving an 800 million year window for life to emerge after the Earth’s crust stabilized around 4.3 billion years ago.

Recent discoveries have significantly narrowed this timeframe. A study by Matthew S. Dodd and others, published in Nature in March 2017, described possible fossil microorganisms from 3.77 to 4.28 billion years ago, found in ancient hydrothermal vent sediment in Quebec, Canada. Similarly, Elizabeth A. Bell and colleagues suggested a biological origin for graphite inclusions found in a 4.1 billion-year-old zircon from Jack Hills, Western Australia.

Consequently, it appears that life may have emerged very early in Earth's history, during the Hadean era, which spans from 4.6 to 4 billion years ago. This period was marked by extreme geological upheaval and catastrophic events, including the collision with the planetoid Theia, which led to the formation of the Moon, alongside a prolonged bombardment of comets and asteroids caused by the orbital shifts of Jupiter and other outer planets.

Chandra Wickramasinghe and fellow researchers assert that it is highly improbable for life to have spontaneously arisen on Earth during such a tumultuous period:

Rather we think it more reasonable to suggest that the particular evidence of microbial life in the Canadian rocks was delivered by cometary bolides, only to be instantly destroyed or carbonized on impact. The conditions that would most likely to have prevailed near the impact-riddled Earth’s surface 4.1 – 4.23 billion years ago were too hot even for simple organic molecules to survive let alone evolve into living complexity. This leaves panspermia as the most plausible valid option for the origin of terrestrial life; the first microbes were most likely delivered to the planet along with impacting comets and meteorites. [E.J. Steele et al., “Cause of Cambrian Explosion — Terrestrial or Cosmic?” (2018)]

Thus, panspermia posits that life has an extraterrestrial origin:

In our considered view the totality of the multifactorial data and critical analyses assembled by Fred Hoyle, Chandra Wickramasinghe and their many colleagues leads to the bare minimum yet plausible scientific conclusion that life was seeded here on Earth by life-bearing comets as soon as conditions on Earth allowed it to flourish (at or just before 4.1 billion years ago); and living organisms such as space-resistant and space-hardy bacteria, viruses, more complex eukaryotic cells and organisms (e.g. Tardigrades), perhaps even fertilized ova and plant seeds, may have been continuously delivered ever since to Earth helping to drive further the progress of terrestrial biological evolution. This process, since the time of Lord Kelvin (1871) and Svante Arrhenius (1908) has the scientific name “Panspermia”. [E.J. Steele et al., “Cause of Cambrian Explosion — Terrestrial or Cosmic?” (2018)]

Read the other parts of this story

• 2/6 — Comets as vectors of life
• 3/6 — Evolution driven by retroviruses and extraterrestrial octopuses
• 4/6 — Interstellar bacteria and mass extinctions
• 5/6 — The biological Big Bang
• 6/6 — An eternal and uncreated Universe