Daily Bulletin


The Conversation

  • Written by The Conversation
imageThe site of the Apex chert once thought to hold the oldest fossil found on Earth.Martin Brasier, Author provided

Less than 10km outside Marble Bar in the Pilbara region of Western Australia lies one of the more famous sites for scientific research in Australia. Around a quarter of a century ago, UCLA palaeontologist James William Schopf discovered tiny filaments preserved within a silica-rich rock, the so-called Apex chert.

These were interpreted as the fossilised remains of primitive filamentous bacteria and thus thought to constitute the earliest known evidence for life on Earth, dated at 3.46 billion years old.

imageApex chert filaments, once interpreted as Earth’s oldest microfossils.Martin Brasier, Author provided

With the technology available to researchers at that time this was a reasonable interpretation. The sizes of the filaments (mostly 1-20 micrometers in diameter) were comparable to known filamentous bacteria and they had an internal structure that resembled multiple cells joined in chains.

During the following decade these filaments became embedded in both the textbook and popular science literature as Earth’s oldest microfossils.

They were also heralded as the standard against which other possible signs of ancient (or even extra-terrestrial) microbes should be judged.

The Apex microfossil debate

Everything changed in 2002 when a team led by Oxford palaeobiologist Martin Brasier questioned the authenticity of the microfossils .

Brasier and colleagues had re-interpreted the geological setting of the filaments, demonstrating that they were trapped in rocks that formed at high temperatures during volcanic activity. This brought into doubt the initial interpretation by Schopf.

Re-examination of the filaments under the microscope revealed that some appeared to branch and others followed the edges of mineral crystals.

These new findings led the Brasier group to propose that the filaments were not microfossils. Instead they were merely bits of carbon, arranged in roughly filamentous patterns around crystal boundaries, probably formed by hot fluids.

In the ensuing decade or so the Apex microfossil debate has been intense. Although it is now accepted that the geological setting is likely a hydrothermal one, this has not diminished the Schopf group’s belief in the authenticity of the microfossils.

They’re now suggesting the filaments are fossils of heat-loving (thermophilic) bacteria, similar to those found around deep-sea hydrothermal vents today.

On the other side of the debate, the Brasier group presented more detailed geological and microscopic analysis consistent with the filaments being non-biological artefacts.

A scientific stalemate had been reached.

Not everything that looks like biology is biology

In collaboration with the late Professor Brasier, we have now used high spatial resolution electron microscopy techniques to investigate the detailed structure and chemical composition of the filaments.

This research, published this week in the Proceedings of the National Academy of Sciences, has confirmed that the Apex filaments are not microfossils. Instead, they are mineral artefacts, comprising stacks of silicate grains onto which later carbon adsorbed.

Our data provided a picture of the morphology and chemistry of the filaments at a spatial scale up to one hundred times better than previous studies. At this scale it becomes apparent that the filaments are made of hundreds of plate-like grains of a potassium and barium rich silicate mineral.

imageElectron microscope image of part of an Apex filament showing stacks of silicate grains (green) and iron minerals (red) that have been coated by later carbon (yellow)Martin Saunders, Author provided

These grains are similar in appearance to common mica that you might see glistening in granite tables around Australia. Although carbon is present in the filaments, its distribution is incompatible with any known biological morphology.

Today mica-like minerals are used to clean up oil spills due to their very high capacity to adsorb (attract to their surface) hydrocarbons. We believe that the carbon in the Apex filaments was arranged by a similar process.

While the lower resolution techniques previously employed allow for a potential biological interpretation, our high resolution data shows that the arrangement and distribution of the carbon within the minerals does not support the biological hypothesis.

The supposed cellular compartments have very inconsistent lengths, plus length/width ratios that match crystal growth patterns but are unlike any known microbial cells. The carbon is found to have entered the filaments after the formation of the surrounding minerals, again inconsistent with it being the in situ remains of bacteria.

What does this all mean for the search for early life?

The field of early life research is fraught with difficulty. Data initially interpreted as biological in origin are often reinterpreted at a later date as having a (less exciting) geological explanation. As new analytical techniques become available, accepted paradigms may have to be questioned.

While our latest research does not really move the goalposts for when life first originated on Earth – there are robust microfossils only a few million years younger than the Apex material – it emphasises that not everything that looks like life really is life.

Perhaps most importantly it shows that microstructures that appear to tick all the boxes for biology when examined down to the micrometre scale, can fail some of these same criteria when examined at the sub-micrometre scale. This may usher in a new way of analysing possible signs of life in the future, on Earth or further afield.

David Wacey receives funding from the Australian Research Council and the European Commission. He is affiliated with the University of Bristol, UK.

Martin Saunders receives funding from the Australian Research Council.

Authors: The Conversation

Read more http://theconversation.com/a-3-5-billion-year-old-pilbara-find-is-not-the-oldest-fossil-so-what-is-it-40482

Writers Wanted

NZ needs a plan to help migrant workers pick fruit and veg, or prices will soar and farms go bust

arrow_forward

Thailand at a critical juncture with pro-democracy protesters again set to clash with police

arrow_forward

So you think economic downturns cost lives? Our findings show they don't

arrow_forward

The Conversation
INTERWEBS DIGITAL AGENCY

Politics

Prime Minister Interview with Ben Fordham, 2GB

BEN FORDHAM: Scott Morrison, good morning to you.    PRIME MINISTER: Good morning, Ben. How are you?    FORDHAM: Good. How many days have you got to go?   PRIME MINISTER: I've got another we...

Scott Morrison - avatar Scott Morrison

Prime Minister Interview with Kieran Gilbert, Sky News

KIERAN GILBERT: Kieran Gilbert here with you and the Prime Minister joins me. Prime Minister, thanks so much for your time.  PRIME MINISTER: G'day Kieran.  GILBERT: An assumption a vaccine is ...

Daily Bulletin - avatar Daily Bulletin

Did BLM Really Change the US Police Work?

The Black Lives Matter (BLM) movement has proven that the power of the state rests in the hands of the people it governs. Following the death of 46-year-old black American George Floyd in a case of ...

a Guest Writer - avatar a Guest Writer

Business News

Cybersecurity data means nothing to business leaders without context

Top business leaders are starting to realise the widespread impact a cyberattack can have on a business. Unfortunately, according to a study by Forrester Consulting commissioned by Tenable, some...

Scott McKinnel, ANZ Country Manager, Tenable - avatar Scott McKinnel, ANZ Country Manager, Tenable

InteliCare triple winner at prestigious national technology awards

InteliCare triple winner at prestigious national technology awards Intelicare wins each nominated category and takes out overall category at national technology 2020 iAwards. Company wins overal...

Media Release - avatar Media Release

Arriba Group Founder, Marcella Romero, wins CEO Magazine’s Managing Director of the Year

Founder and Managing Director of the Arriba Group, Marcella Romero, has won Managing Director of the Year at last night’s The CEO Magazine’s Executive of the Year Awards. The CEO Magazine's Ex...

Lanham Media - avatar Lanham Media



News Co Media Group

Content & Technology Connecting Global Audiences

More Information - Less Opinion