If you can recall high school biology class, you might remember hearing the term abiogenesis. In short, it’s the idea that life arose from nonliving substances via natural chemical reactions. Most biologists who study this theory hold that it was a very lengthy process with numerous incremental steps of increasing complexity. Theories abound about the order in which these chemical reactions took place, but most of them share the idea that conditions on Earth were radically different billions of years ago. Many also suggest that the earliest chemical reactions were set in motion by an energetic input – lightning, the impact of fast-moving meteorites, radiation, etc. 

Although this is currently the prevailing theory in biology, there are other models. One that has waxed and waned in popularity is known as panspermia—a Greek term meaning “all seed.” This theory suggests that life exists elsewhere in the universe, and it arrived on Earth by way of space dust, meteors, asteroids, and the like. Although it is a darling of contemporary Sci-Fi writers, the earliest known mention of panspermia is found in the writings of the Greek philosopher Anaxagoras, who was born around 500 BC. In the years since, it has undergone numerous revisions and additions, and now includes the possibility of inadvertent or deliberate seeding of the Earth by space faring aliens. The relatively recent discoveries of microscopic life that can survive the rigors of space and atmospheric reentry supports the possibility that simple forms of life could simply fall from the sky.

The most influential proponents of panspermia in the 20th Century were Sir Fred Hoyle and Chandra Wickramasinghe, who together developed a model of panspermia that bears their names. They contended that life on Earth is at least partially extraterrestrial in origin, and suggest that viruses and bacteria have continued to fall to Earth from space, triggering many pandemics throughout history. They also used panspermia to support the cosmic origin of life, including the concept of God, lending credence to the “intelligent design” model.

Today, panspermia is espoused by very few serious theorists. The most common complaint against it is that it doesn’t actually address the question of the origin of life, focusing instead on the ways that life could be spread from one celestial body to another. To address this concern, the latter iteration of the Hoyle—Wickramasinghe panspermia model included the hypothesis that abiogenesis originally took place near the center of the Milky Way, and life was then disseminated throughout the galaxy by the various mechanisms of panspermia.

Wickramasinghe continues to support panspermia, and as recently as 2018 he published Cause of Cambrian Explosion – Terrestrial or Cosmic?,  a paper with thirty-plus coauthors, which proposed that the frozen eggs of alien cephalopods were transported to Earth by meteors, giving rise to the sudden diversification seen in the Cambrian fossil record. Despite making a splash in mainstream media, the paper was roundly criticized by the scientific community, and characterized as pseudoscience.  

The next time you find yourself contemplating the origins of life, consider the idea of random cosmic events (or, if you prefer, a benevolent celestial gardener) spreading the seeds of life across the millions of habitable planets in the universe. And while you ponder that, stay tuned to the Planetary Broadcast Network, and we’ll make sure you’re among the first to know if more frozen alien eggs fall from heavens.