Ancient microorganisms form rocks of Stromatolite 34 million years old

Stromatolite rock is an ancient sedimentary rock structure with a round or cylindrical top shape formed in layers of shallow water through long-term geological transformation. Now researchers from the California Institute of Technology (Caltech) and the Jet Motion Laboratory (JPL) have provided evidence that some of the oldest stromatolites on Earth are formed by pants. microorganisms in the same age. This is a finding 'that adds to our understanding of the first life form on Earth,' according to JPL's cosmologist Abigail Allwood.

The research results published in the latest issue of the Proceedings of the National Academy of Sciences (PNAS) also provide a new achievement in the search for signs of life on Mars. ' Stromatolite stones formed by accumulate deposits around a nucleus in shallow water, ' said John Grotzinger, professor of geology at Caltech Institute. 'Initially, they have a wave-like layer, over time, these waves split into separate cylinders that grow taller.'

Geologists have long known that the majority of ancient stromatolite rocks half a million years they studied are of biological origin; they are formed with the action of microorganisms growing in a thin layer on the ocean floor.

How did the formation process take place? The surface of microorganisms is covered with a layer of mucus to 'trap' the particles that pass. In addition, microorganisms also grow silk threads that grab them when they pass.

'As a result, even if these microorganisms are in any position below the ocean, the particles will be entangled,' says Grotzinger.

Therefore, it is agreed that the dark band on each stromatolite is the old organic matter layer: 'That is the remnant where the old' nets' existed.
But if you look back at the beginning of the Archean period of 3.45 million years in geological history, everything does not seem so simple.

'Because during this period stromatolite rocks were formed, the geological process continued to work,' says Grotzinger. The stromatolite rocks are increasingly pushed deeper towards the center of the Earth, and they are influenced by an increasing flow of heat. This is a difficulty in understanding the organic origin of stromatolite, because heat alters, even decomposes organic matter. 'Hydrocarbons disappear,' he said. 'The only remaining object is carbon.'

That's why geologists continue to argue over the question of whether carbon found in these ancient rocks is a sign of life.

It can easily be proved that in younger rocks, life exists - just remove the organic matter in it, and prove that it is derived from microorganisms. But this simple method is not applicable in analyzing ancient stromatolite blocks.'When the stone is old and subjected to many effects of heat and mechanical force,' Grotzinger said, 'what you need to consider is its texture and form.'

This is a rare ancient surface image of conical stromatolite stone in the shallow layer of the reef. (Photo: Abigail Allwood)

And that's exactly what Allwood and Grotzinger have done with the samples collected at Strelley Pool, Western Australia. These patterns, according to Grotzinger, 'are well protected unbelievably.'Dark lines, traces of organic matter have the same characteristics as in young rocks. This is difficult to explain without a biological mechanism. '

'We knew from the beginning of the study that this is a collection of tromatolite rocks almost certainly formed by early Archean microorganisms,' Allwood added, 'but there is no direct evidence. about the ancient existence of microorganisms. There are no microbial fossils, no organic matter or even a trace of confirmation of the microbiological structure as commonly found in sedimentary rocks formed from microorganisms. '

Allwood therefore tried to find other forms of evidence to test the biological hypothesis, by studying what she called 'micro-scale structures, different types of structures in stromatolite and - important is - organic layers that look like real fossil traces of microorganisms inside the rock. '

What she saw was 'layers of individual organic matter, grid-type running around the rock from one side to the other.' She also discovered microbiological nets into clear sediments, which dismissed the previous idea that organic matter had only just penetrated into recent rocks, rather than deposits. sediment exists from the beginning when rock formation. 'In addition,' Allwood notes, 'Raman spectroscopy shows that organic matter has been introduced at the same temperature as the main rock, which again confirms that organic is not a new substance introduced into the mass. Rock later. '

Allwood said she and Grotzinger and her colleagues gathered enough evidence to make sure that these stromatolite rocks are of biological origin.'I dare say that the deeper we dig into these rocks, the more evidence of the early Archean life and early ecosystems on Earth will be found.'

This is not easy, because it is difficult to prove that life has existed for so long in geological data.'More and more evidence has shown that life existed at that time, but only indirect evidence. Direct evidence of micro-microorganisms is still very rare because the blocks are not well protected over time, ' Allwoold said. 'I think most people think that Archean-era stones are not preserved well enough to reveal information about their organic origins.'

The result is not only the information about life on Earth.

One of the things that helped me understand stromatolites, ' Allwood revealed, ' is that I understand that if microbial populations once flourished in Saturn, stromatolite and microbial reefs are the forms. Most easily explored among all the remaining traces. Moreover, they are particularly likely to be formed in volatile conditions and mineral deposition. But to successfully interpret stromatolite structure, we need more detailed understanding of their formation. '

The Agouron Institute provides partial funding for the study; and Allwood is supported by NASA's postdoctoral training program.

Journal reference:
1. Allwood et al.Inaugural Article: Controls on development and diversity of Early Archean stromatolites.Proceedings of the National Academy of Sciences, 2009;106 (24): 9548 DOI: 10.1073 / pnas.0903323106