Studying Earth Science is not exclusively studying rocks and, as anyone who has been around here before knows, the rocks are not actually my favourite bit. Life, specifically the possibility of extraterrestrial life, I find far more exciting. The fundamental place to start with this topic is to look at the origins of life on Earth. This is, along with many questions in STEM at uni level, a question that is yet to be definitively answered. I really enjoy this about studying science above A-Level; learning about things that are still ongoing scientific debates is fascinating and allows you to form your own opinion rather than being told what to believe. We first encountered the ‘where did life come from?’ question in the first term of first year and have come back to it in numerous courses since. Now, it’s time to discuss it on here.
Image credit Elena Mozhvilo via Unsplash
So, life has obviously evolved on Earth (or you wouldn’t be reading this right now) and looking at the tree of life and evolution, it most likely only originated once. All life on earth comes from the same initial life ‘spawning’ (for want of a better word) event. This traces everything, every species, back to the last universal common ancestor. We can tell this by looking at the similarities of the molecules that make up all life and their limited building blocks of mostly C, H, N, P, and H20.
We know that specific conditions are needed for life to evolve. Earth is often referred to as being in a ‘goldilocks’ position. Where it is at the right distance from the sun to be not too hot and not too cold, and to therefore support liquid water. For a planet to meet the requirements for habitability it must have surface water and temperatures between the boiling and freezing point of water. Or at least we think this is what is needed.
Now there is a couple hypothesis as to how life got to being on this goldilocks planet of ours. Did it originate here, did it get delivered here by a meteorite, maybe either one, maybe neither, we don’t know. But let’s explore the ideas.
So one of the more famous theories is the Oparin-Haldane hypothesis, also know as the ‘primordial soup’ theory. This theory essentially says that Earth had a soupy sea full of lots of organic molecules and the building blocks for life floating around in it. This soup was then struck by lightning or some other energy source to trigger the start of life. This was suggested in the 1930s and was very popular, with an experiment in the 1950s mimicking this event even yielding amino acids. However, since then scientists have rethought what the composition of the atmosphere would have been early on in Earth's history so it’s results are no longer seen as valid.
The next theory is the panspermia hypothesis. This one suggests that life originated elsewhere and was brought to earth already formed on a meterorite. Perhaps it was prebiotic material that was delivered, or perhaps DNA or even microbes themselves. Some potential evidence for this can be seen in carbonaceous chondrites, a specific type of meteorite, which have been shown to contain low concentrations of all of the 5 primary nucleobases used in DNA. But this is not enough to tell us this is how life formed, nucleobases after all are not forms of life.
Finally, and my favourite, is that life formed around a hydrothermal vent. Black smokers are (or the ancient equivalent of them), places on the se floor where very hot water comes out of alkali vents could provide the energy needed to fuel the origins of chemosynthetic life. This just means life that instead of being photosynthetic and relying on energy from the sun, they rely on energy from chemical reactions. This is also a theory for how life may exist on the icy moons of Jupiter such as Io and Europa, hydrothermal vents in their interior oceans.
There are obviously no records of how life actually did evolve, no helpful microorganism to tell us what happened, and so far no evidence that is by far unanimous as to what theory is correct. So that’s up to you what you want to believe, and up to scientists to keep searching for the answers.
All info here has come from various lecture notes I've made during my 2.5 years studying Earth Science, hence the lack of links, but a quick google search can get you well on the way to finding more!
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