The world's oldest fossil?
Where is the world's oldest fossil, and how can we be sure it's really evidence of life? Georgia Mills spoke to Dominic Papineau from UCL, whose interest in life elsewhere in the Universe is taking him deep into the past...
Dominic - I’m going about it the only way that technologically we currently can, although we do have rovers that are capable on Mars to directly search for signs of life and there’s also the SETI programme. My approach is mostly looking at the very distant past on the early Earth and trying to identify signs of life and understand the environmental conditions where these microbial communities were living because we’re obviously talking about microorganisms. At that time there were no trees, fungus, or other animals or this microscopic life that we see today wasn’t there in most of the Archean probably.
Georgia - So you’re searching for something very, very small - how do you even start?
Dominic - You need to target, I think, the right rocks. You can narrow it down to some of the oldest rock sequences our there and this rock sequence that I’ve been at in 2008 in northern Quebec, the Nuvvuagittuq supercrustal belt, is known to be at least Eoarchean in age since 2004. The Eoarchean is the first time period this sedimentary rock record appears.
Georgia - Was it case of hey, these rocks are really, really old, let’s have a look in them, and then you’re just hoping you might find something?
Dominic - Not quite. The Nuvvuagittuq supracrustal belt is about 3 kilometres in length and the banded iron formation unit that is smack in the middle of this has been known for more than a decade now. I was studying banded iron formations so I was interested in these particular biffs as well because these are very ancient. They’re as old as those I was looking for from Isoa and the island of Akilia in Greenland, and that was going to be another example of eoarchean banded iron formations. So I went there in the hope of finding similar things as what other people had found and I myself had found. Even better I found the red banded iron formations with concretions so ‘eureka.’
Georgia - Is the combination of the fact that they were very old and the type of rock that made them of interest to you?
Dominic - Yes, exactly.
Georgia - When you found something, what did you find - what did it look like?
Dominic - I was there specifically for the banded iron formation so I walked a long strike back and forth. It was striking to me that at one particular site, very localised, there were outcrops of this red banded iron formation. When I was walking on it I was carefully looking at the rock and I could see these rounded spherical structures which I had seen in the Hammersley before. So I knew that these concretions had something, so I sampled them and that’s exactly where we found the microfossils.
Georgia - You’ve got a selection of these rocks in your cabinet in your office. They’re very pretty but I would never expect they contained any kind of life.
Dominic - If you go to the Museum of Natural History, you can see very often that marine animal fossils are preserved in these rounded bits of rock. They’re called concretions; they’re called limestone concretions. They have various names and the reality is that in geology we don’t really have a good explanation for how they formed these particular structures. But we know that in the recent young geological record that they’re associated frequently with animal fossils.
Georgia - Can we go and have a look at your fossils then?
Dominic - Sure… This is what we see.
Georgia - Oh Wow!
Dominic - So that’s what you say - oh wow.
Georgia - So this is a slice of the rock from your office - a very thin slice under a microscope.
Dominic - They’re a little thicker than the usual ones so we’re experimenting with different techniques now. Yes, this is what these things look like.
Georgia - Id’d have a photo of this in my house. It’s a bit like Jackson Pollock or something - a sort of white background and then little flecks of red and black.
Dominic - And there’s a twisting like a spiral.
Georgia - Oh yeah. That’s like a corkscrew.
Georgia - In the slide, amongst the flecks of red you can clearly see a black spiraling tendril. Dominic suggests this could have been made by a microscopic creature, maybe similar to modern day bacteria. But could these shapes simply be caused by geological processes?
Dominic - So far we’ve had one substantial criticism and that is that there are these so-called chemical gardens that can grow tubular structures. Other such non-biological experiments have been successful at growing these filaments that are sometimes twisted so they have morphologies that look like they could potentially be analogues to features that we observe. But if we just consider this kind of comparison based on the morphology, this is one of the main reasons why there’s been so much controversy in the past. It’s because there's very little lines of evidence. But if you consider the bulk of our lines of evidence - we have twelve independent lines of evidence - so I think this is bullet proof.
Georgia - The twelve lines of evidence are the various shapes and chemicals found in the rock, The patterns, the radioactive isotopes, they’ve all been associated with life. Some on their own can appear without the presence of life but, all together, Dominic is confident he has the oldest evidence of life on Earth. Which is pretty exciting...
Dominic - I celebrated with my wife. But when my student, Matt Dodd, took these images and did the due diligence, and he catalogued the images and mapped everything that he was looking at as I instructed him, he brought to me this very compelling images. At some point he brought me this fossil with the twisted stalks and these were very compelling in my opinion. So this was ‘yay- we have the oldest fossils!’. It’s exciting but, ultimately, it’s what it implies with respect to the rapidity that life arises on the planetary surface. The conditions in which it arises has implications for evolutionary biology because many of these microfossils that we find are similar to microorganisms that are living today in these kinds of environments. There’s a continuity in biology that tells us that some organisms haven’t changed much over all this time so it has implications for the origins of life. It has implications for exobiology. I think it’s an important discovery but it’s one that’s going to be followed by many more to come.