Sulphur-loving microbes might be oldest life A microbial bacterial fossil find is being hailed as proof that life existed in the oxygen-free environment of Earth, 3.4 billion years ago. The Strelley Pool Formation in Western Australia was once a beach, but is now more than 100 Km inland near(ish) the town of Marble Bar, and is popular among paleontologists because of the …
Hmm, you've never ridden the Prague Metro during rush-hour in the summer then?
Take deep breath, get on and try to hold it until your destination. This doesn't work, but even air that smells like the inside of a hod-carrier's jockstrap is ok when you're already cross-eyed, dizzy and blue-faced from asphyxiation...
Most minerals form some sort of crystalline / regular structure, so structural regularity is only an indicator.
What really tips the balance to believability (pending confirmation of measurements etc) is the "depletion of C-12". I'm in no way an expert on isotopes & metabolism, so I'm not sure exactly what that means. However I do know that living organisms metabolize radioactive isotopes in a way that dead ones don't, allowing for things such as C-14 dating... so it seems to me to be a valid indicator of 'living organisms'
Living organisms preferentially metabolise C-12 over C-13, so their surroundings tend to show a depletion of C-12. There's a similar change in ratio when organisms metabolise sulfur.
This is a fascinating find as it pushes signs of life back to a point within 400 My of the end of the Late Heavy Bombardment which would have plastered the whole planet with massive craters - but which also brought a sizeable amount of the Earth's water.
There are practically no sedimentary rocks of this age left in the world, so this might be the best we can get for now. Although there is a chance fossils from an older rock could be included in a younger conglomerate or breccia. But pretty much every rock of this age has been through at least one phase of metamorphosis which tends to erase fossils as the rocks get cooked.
There is some evidence of life in even older rocks (3.8 Gy) from the Isua Complex in Western Greenland. Some sequences contain traces of graphite enriched C-12 suggestive that they originally came from sediments including living organisms. However, the Isua rocks are in a greenstone belt which has been heavily metamorphosed into gneiss and they've lost their original sedimentary features and any fossils have been baked away.
'However I do know that living organisms metabolize radioactive isotopes in a way that dead ones don't, allowing for things such as C-14 dating... so it seems to me to be a valid indicator of 'living organisms''
C-14 is useless for dating almost all fossils as it only has a 5.73ky half-life. IIRC the oldest samples reliably dated using C-14 are only about 60ky.
It can be used to date living and recently deceased organic material because living creatures take up C-14 throughout their life at a known ratio to the stable carbon isotopes. When they die, the uptake of C-14 stops and it begins to decay at a known rate. By measuring the actual ratio found in the sample you can derive an age for the material.
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