For those who don't know what the Fermi paradox is (
see here for a great summary video): the galaxy is 10bn years old, and it would only take an alien civilisation 0.002bn years to colonise the whole thing. There are 6bn warm rocky Earth-like planets in the galaxy. For the sake of argument, imagine 0.1% generate intelligent species. Then imagine 0.1% of those species end up spreading out through space and reaching our field of view. That means we'd see evidence of 6,000 civilisations near our solar system - but we see nothing. Why?
The issue with many proposed solutions to the Fermi paradox is that they must apply perfectly to those 6,000 civilisations independently. For example, aliens could prefer to exist in virtual reality than explore the physical universe - but would that consistently happen every time to 6,000 separate civilisations?
Surely the most relevant aspect of the Fermi paradox is time. The galaxy has been producing stars and planets for 10bn years. Earth has existed for 4.54bn of those years. The earliest known life formed on Earth 4bn years ago (Ga). However, there is some evidence to suggest it may have formed as early as 4.5 Ga (
source). Life then existed on Earth as single celled archaea/bacteria until 2.1 Ga, when the first eukaryotes developed. After that, key milestones happened relatively quickly – multicellular life appeared 1.6 Ga, earliest animals 0.8 Ga, dinosaurs 0.2 Ga, mammals 0.1 Ga, primates 0.08 Ga, earliest humans 0.008 Ga, behaviourally modern humans 0.00005 Ga, and the first human reached space 0.00000006 Ga.
It's been proposed that the development of the first eukaryotes (eukaryogenesis) was the single most important milestone in the history of life, and it's so remarkable that it could be the only time in the history of the galaxy that it's happened, and therefore the solution to the Fermi paradox. A eukaryote has a cell membrane and a nucleus, and is 1,000 times bigger than an archaea/bacteria. It can produce far more energy, and this energy allows for greater complexity. It probably happened when a bacterium "swallowed" an archaea, but instead of digesting it, the two started a symbiotic relationship where the archaea started producing energy for the bacterium. It may also have
involved a giant virus adding its genetic factory mechanism into the mix. In other words, it was extremely unlikely to have happened.
The galaxy could be full of planets hosting archaea/bacteria, but Earth could be the first one where eukaryogenesis miraculously happened and is the "great filter" which we have successfully passed to become the very first intelligent form of life in the galaxy - there are 3 major reasons for why:
- The appearance of the eukaryote took much more time than the appearance of life itself: It took 0.04-0.5bn years for archaea/bacteria to appear on Earth, but it took a whopping 1.9-2.4bn years for that early life to become eukaryotic. In other words, it took far less time for life to spontaneously develop from a lifeless Earth than it took for that life to generate a eukaryote, which is crazy when you think about it
- The appearance of the eukaryote took more time than every other evolutionary step combined: The 1.9-2.4bn years that eukaryogenesis took is 42-53% of the entire history of life. It's 19-24% of the age of the galaxy itself
- It only happened once: Once eukaryotes developed, multicellular organisms developed independently, over 40 seperate times. However, eukaryogenesis only happened once. Every cell in every eukaryote, including you and me, is descended from that first eukaryote. All those trillions of interactions between bacteria, archaea and giant viruses, and in only one situation did they produce a eukaryote.
This paper analyses the timing of evolutionary transitions and concludes that, "the expected evolutionary transition times likely exceed the lifetime of Earth, perhaps by many orders of magnitude". In other words, it's exceptionally lucky for intelligent life to have emerged as quickly as it did, even though it took 4.5bn years (of the galaxy's 10bn year timespan). It also mentions that our sun's increasing luminosity will render the Earth uninhabitable in 0.8-1.3bn years, so we're pretty much just in time!
Earth has been the perfect cradle for life (
source) - it's had Jupiter nearby to suck up dangerous meteors, a perfectly sized moon to enable tides, tectonic plates which encourage rich minerals to bubble up to the crust, and it's got a rotating metal core which produces a magnetic field to protect from cosmic rays. And yet it's still taken life all this time to produce an intelligent civilisation.
I've been researching the Fermi paradox for a while and eukaryogenesis is such a compelling topic, it's now in my view the single reason why we see no evidence of aliens. Thanks for reading.
en.wikipedia.org
www.nature.com
www.theguardian.com
maritime-executive.com
