What if life on Earth is older than Earth itself, and arrived aboard an interstellar rock from within the unexplored hinterlands of our cosmos?
Space rocks like asteroids and comets abound in our cosmos. Stars are forming and dying constantly in the Milky Way and other galaxies. Planetary bodies collide. The resulting debris of rocks drift and wander through space as asteroids and comets, and eventually crash into other celestial bodies.
Meteoroids (pieces of asteroids, comets, planets, satellite bodies, etc.) pelt down on Earth every day. While most are hardly noticeable, the size of small stones and sand grains, occasionally Earth’s path crosses with larger rocky fragments. Thanks to Earth’s atmosphere, most of these meteoroids burn up on contact, and what remains arrives on the ground as fine space dusti known as micrometeorites. Once in a while, boulder-sized meteorites too, make it to the ground causing impact on the Earth’s surface. The much larger asteroids leave indelible marks in the form of deep impact craters, and Earth’s vibrant history is full of such examples. The most famous and among the largest craters on Earth is the Chicxulub Crater in Yucatan, Mexico, which is nearly 180 km. wide and 20 km. deep! The meteorite that caused it is known to have played a big role in perpetrating one of the five biggest mass extinctions on Earth some 65 million years ago, when more than 70 per cent of all species died off including all non-avian dinosaursii.
Perhaps the answers to the single most important question pertaining to life on our planet – How did life on Earth begin? – lies in one such space rock that may have arrived carrying microscopic living things over 4 billion years ago, seeding life here on our planet. Perhaps the answers to the question of origin of life on Earth continue to elude us because we are looking for them in all the wrong places, namely, the Earth. We still cannot firmly say or reliably demonstrate how and when the first spark of life was infused in lifeless organic matter on our young, primordial planet. And naturally many theories and opinions attempt to provide the ultimate answers. But what if life did not originate on the ‘pale blue dot’ at all? What if life on Earth is older than Earth itself, and arrived aboard an interstellar rock from within the unexplored hinterlands of our cosmos? Could the first living inhabitants of Earth have arrived as aliens?
The Controversial Panspermia Theory
As far-fetched and implausible as it may sound, this idea has been in circulation for quite a while now. Called ‘panspermia’, this controversial theory suggests that life originated on some other planet, which suffered collisions with asteroids, comets, or other planetary bodies, throwing up space rocks that were once part of that planet. Some of these rocks took with it strains of microbial life and coursed through space as asteroids or comets, until they hit Earth, landing with said aliens which took up residence here, adapting, colonising and evolving as Earthlings! In short, an interplanetary exchange of life is a norm within the observable universe, according to the panspermia hypothesis.
Yes. Panspermiaiii is an unproven theory and has often been dismissed as a figment of mad person’s imagination. But, in the recent past, panspermia has been gaining credibility within the scientific community for a multitude of reasons.
In recent years, scientists have dredged up evidence of life on Earth as old as 3.8 billion years to 4.28 billion years. Up until now, it was thought that the planet wasn’t conducive to life till about four billion years ago. But newer evidence keeps pushing the date further back, which raises a fair question. Considering how gradual the process of evolution of life on Earth has been and how complex it has gotten, upon tracing the evolutionary trajectory backwards, it is hard to fathom that cellular life with all its basic molecular ingredients could have formed within so short a span of time that had elapsed since the birth of planet Earth ~4.54 billion years ago. This perspective hints at the possibility that life may already have originated on some other planet before Earth was born. Perhaps?
It has now been conclusively proven that the basic organic ingredients in the recipe for life such as water, and carbon-based molecules such as amino acids and sugars are found in space. A meteorite named Murchison, that crashed into Australia in the 1960s, contained traces of all types of amino acids found on Earth and more. In 2003, the Hayabusa spacecraft was launched by the Japan Aerospace Exploration Agency with the mission to collect samples from asteroid Itokawa and return to Earth to allow scientists to study the samples for traces of life-supporting ingredients. Years of analysing the Itokawa particles has substantially established that many asteroids do carry water and organic matter.
The credibility of the idea of panspermia relies largely on proving that microbial life such as bacteria can survive in space – the hostile conditions of vacuum, extreme temperatures, and severe UV radiation – and long journeys across several light years (which is a measure of distance and not time as often wrongly interpreted) and vast time spans. Space missions have been conducted to test the microorganisms in space such as the deinococcus bacteria. Deinococcus had already been known to survive radiation, and they even showed us that they could survive up to eight years in space. We already know of several examples of microbe extremophiles (organisms that can survive in extreme environments) right here on Earth which are able to survive extreme temperatures, altitudes, toxicity, radioactivity and anaerobic conditions. On multiple occasions, scientists have also successfully revived microbes which have remained in dormant state for millions of years in a seabed and Antarctic ice, for example.
These are some reasons that warrant hypothesising about the extraterrestrial origins of life which eventually made it to Earth. Not only is it fascinating to think about the apparent celestial origins of organic molecules that make up you and me, but also the fact that there may be space rocks – that were once part of Earth – which were ejected during the many collisions that Earth has suffered in the past, carrying remnants of life ready to seed another planet!
Though scientifically unproven and untested, the ‘Panspermia’ theory is beginning to seem like a tantalising possibility. And the bold vision of panspermia is not limited to our solar system – it goes intergalactic and interstellar!
iEvery day, 50-150 meteorites weighing over ~10 g. crash into the Earth’s surface. Earth is showered with 20,000-30,000 tonnes of space dust (micrometeorites) annually.
iiYes, all birds are dinosaurs, and most bird species survived the Cretaceous-Paleogene (K-T) mass extinction event 65 million years ago.
iiiThe idea of ‘Panspermia’ took seed long ago when the Greek philosopher Anaxagoras (500–428 BCE) posited that “the seeds of life are present everywhere in the universe”. Anaxagoras coined the term ‘panspermia’ which according to him meant life traversing between planets as “seed”.
About the author: Purva Variyar is a conservationist, science communicator and conservation writer. She works with the Wildlife Conservation Trust and has previously worked with Sanctuary Nature Foundation and The Gerry Martin Project.
Disclaimer: The author is associated with Wildlife Conservation Trust. The views and opinions expressed in the article are her own and do not necessarily reflect the views and opinions of Wildlife Conservation Trust.
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