Minerals needed for appearance of life on earth were discovered by SPbU scientists in rock samples found in the vicinity of the Dead Sea. The results of the study and the new concept explaining how life began on our planet were recently published in Scientific Reports (an international scientific journal published by the Nature Publishing Group).

SPbU scientists discovered 5 new minerals (phosphides) in one go, determined their structure and studied their properties. The unique aspect of the discovery lies in the fact that such minerals used to be found only in meteorites. During his presentations given at the SPbU Science Lunch (a traditional meeting between scientists and journalists), S. Britvin, associate professor of the SPbU Department of Crystallography, explained that phosphides were rarely found in terrestrial rocks: only two accidental, isolated finds of that kind had been registered before. And now, among the samples recovered from the Negev Desert and the Transjordan Plateau, the geologists have found a whole assemblage of natural phosphides with different compositions and structures. Their discovery has led to a new hypothesis concerning the beginning of life on earth.

 

New finds

In 2012, the phosphides were discovered and collected on the shores of the Dead Sea by Mikhail Murashko (now am employee of SPbU). It was he who noticed that the samples contained five new minerals, bronze in colour and with metallic lustre, which after the analysis were identified as phosphides. It is only now that they have become well known; back then, not many people knew about phosphides, and M. Murashko was one of those few.  This find was preceded by 47 years of expeditions, trips around countries and continents, undertaken by the St. Petersburg mineralogy enthusiast and ardent collector of rare minerals. Experts estimate that there are about 5,000 types of minerals. Mikhail Murashko has more than 3,800 in his collection, and at least half of them he recovered himself!

Why were the phosphides found near the Dead Sea? Why is this area unique? Not only because it is the scene of many biblical events, it turns out. The Holy Land is also rich geologically: here, in the Negev Desert, on the lands of Israel and Jordan, more than 200 types of minerals have been found. This is a very interesting place but not too well-explored, and it is rather hard to work there, according to Murashko. He first visited this area in 2004, and ever since that time, he has been organizing expeditions to the Dead Sea every year (he returned from the last one in April).

All the work in Israel and Jordan is organized by Evgeny Vapnik, a graduate of Leningrad Mining Institute and now a researcher at Ben-Gurion University (Beersheba, Israel). Evgeny knows, perhaps better than anyone, most of the outcrops of the Hatrurim Formation, and geological и mineralogical studies there without him are impossible… People can work in the desert for six months only, from the end of September to the end of April; in summer even the locals cannot bear the heat. The main difficulty is the need for a lot of water: at temperatures around 400 С°, four or five litres per person are required.

“We do not spend the night in the desert because it is technically difficult to organize. Every morning we travel by car to the place where we conduct research and then walk for five or six kilometres,” M. Murashko said. “Bedrock is well exposed there. There are occurrences up to several dozen metres in size (and this in different parts of the Dead Sea shore, both in Israel and Jordan). If we are lucky, we recover a sample with interesting minerals from the bedrock. But much more often we are confined to exploring rock fragments — found, for instance, in the dry stream channel of the Halamish River. Returning home in the evenings, we study the samples under a binocular microscope and use any other available methods to analyse them...”

M. Murashko found the first phosphides in the desert in 2006-2007. These were, however, well-known phosphides, which had been described before. He started paying particular attention to similar rocks, since now he knew that phosphides could be fund there! After all, the most important aspect of his work as an exploration geologist is to know where to look, and Mikhail Murashko is a recognized expert; during many years of field work, he has polished his skills to perfection. He graduated from Leningrad Mining Institute with a degree in the field of Geological Survey, Prospecting and Exploration Mineral Deposits, then completed a doctoral programme there and defended his candidate’s thesis on the origin of muscovite pegmatites in Irkutsk Oblast. “Muscovite belongs to the mica group,” Murashko explained. “It is an important technical raw material widely used in radio-frequency engineering.” From 1992 and up until recently, M. Murashko had worked independently.  He started a private limited company, ZAO Sistematicheskaya Mineralogia, and began to prospect for and recover rare minerals on commissions from universities, mineralogical museums and collectors.

“Using the existing literature, I choose a rock massif where particular rare minerals could be present. This is not a random search, so I study the paragenesis: I find out beforehand what other minerals coexist with the one that I am searching for. Later, looking at the outcrop itself, I can see where the mineral in question can occur and where it cannot. My education and experience are enough to do that,” M. Murashko said, shrugging his shoulders. 

In the 1990s, for example, Murashko organized an expedition to the Tolbachik Volcano on the Kamchatka Peninsula. He found 2 new minerals among the samples he had brought from there. Later crystallographers confirmed that the minerals indeed were previously unknown. They were officially registered and, on Murashko’s suggestion, named avdoninit and grigorievite (in honour of the mineralogists V. Avdonin and D. Grigoriev, professors from mining institutes of Ekaterinburg and St. Petersburg). Six rare minerals occurring in the Negev Desert and non-existent anywhere else were described by scientists in the 1960s. These minerals were the reason why Murashko went to Israel. Almost all of those described were found, in addition to several dozen previously unknown minerals. 20 of them have already been recognized by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (and probably just two or three of them without Murashko’s participation). A lot of work was performed with participation of Russian scientists from Novosibirsk, Chernogolovka and Krakow.

 

New research

Murashko asked Sergei Britvin, a prominent exert in the fields of mineralogy and crystallography, associate professor of the SPbU Department of Crystallography, to carry out the crystal-chemical analysis of the samples. He chose to engage Britvin because the latter had spent many years studying meteoritic matter; even the title of his candidate’s thesis was “Phosphides in highly metallic meteorites”.

“Only 8 naturally-occurring minerals of this class have been known before; all of them were found in meteoritic matter and only 2 were identified in single grains of terrestrial rock. They were recovered from deposits on the island of Greenland and were supposed to have also originated from meteorites,” S. Britvin explains. “In the samples brought to us from the Holy Land by M. Murashko, however, we found 7 phosphides, including 5 new, previously unknown ones. They are obviously of terrestrial origin (one of the samples, for example, was found in a bulldozer pit!). In April 2015, phosphides were found in the bedrock in Jordan.”

During a meeting with the journalists, S. Britvin demonstrated the miniature scale of the investigation carried out during the analysis of the phosphides. He showed to us a glass needle (a barely seen fibre), which is inserted into the attachment (goniometer head) of the device — a single-crystal X-ray diffractometer. On the slide of his presentation, this fibre (enlarged image) looked like a thick pencil. And right on it, we could barely see a tiny black dot — a single crystal of the phosphide which Sergei Britvin had isolated for the analysis of its structure (see Presentation).

“Five or six years ago, such analysis would have been impossible. The minerals that are found during explorations are often very small, sometimes of just 10 microns or so. Besides, all phosphides are very similar,” Britvin said. “However, SPbU now has a high-technology Research Park with cutting-edge equipment for analysis of substances. At the Resource Centre for X-ray Diffraction Studies, we now can fully explore the crystal structure of minerals in order to confirm beyond doubt that a newly found mineral is indeed new and different from any other previously known.”

M. Murashko told us that S. Britvin is a unique researcher. Few scientists can work with the order of magnitude as small as 10 microns. Here you need a good eye and a firm hand, and also extensive experience in this kind of scientific investigation. According to Murashko, S. Britvin agreed to put aside his other tasks in order to study the phosphides.

The Director of the SPbU Research Centre for X-ray Diffraction Studies Oleg Grunsky told the journalists about the methods used for studying the phosphides and other objects of analysis (X-ray structural analysis, high-resolution diffractometry, X-ray phase analysis, and thermal X-ray diffraction). These methods help to study, for instance, the structure of proteins, the paint formulation used in miniature painting without destroying the work of art, pieces of rust from reactor tubes, ancient artefacts found by archaeologists, etc.

In recent years, SPbU has become one of the global centres for descriptive mineralogy and crystal chemistry. Mineral samples for analysis are sent here from the USA, Great Britain, Germany and other countries. S. Britvin is a discoverer of about 20 new minerals, and approximately the same number he has discovered together with other researchers, while S. Krivovichev has co-discovered 60 new minerals.

 

New hypothesis

Why are phosphides important? Why are they so interesting? The fact is that they contain phosphorus — an element essential for life, which is a key part of organic phosphorous compounds (for instance, adenosine triphosphate (ATP) — the most important carrier of chemical energy in homeothermic species, including the humans), of DNA and RNA. A living cell cannot exist without phosphorus.

“Geochemists believe that phosphides were the source of the initial phosphorus needed for the appearance and development of life on earth. The beginning of life itself, according to the established hypotheses, was connected with the transition of phosphorus from a low level of oxidation in phosphides, through a chain (phosphides — phosphites — polyphosphates — phosphonates — organophosphates), to a high oxidation level, which constitutes the biological form,” Professor S. Krivovichev, who heads the SPbU Department of Crystallography, explained. “Phosphides, however, used to be found only in meteorites. It was believed that any other source of prebiotic phosphorus, of terrestrial origin, did not and could not exist... Our discovery expands the previous understanding. It shows that Archean prebiotic phosphorus could have had terrestrial origin.”

How did it happen? The phosphides were found in the area where the ancient Hatrurim Formation is exposed — a unique complex of rock strata united by the same geological origin. This geological formation, according to what I was told, appeared between 3 and 1.5 million years ago. In ancient time, from below the sediments located in this area, from under the mass of bitumens (hydrocarbon mixtures), methane and other gases rose up and burned. The land burned brightly and fires covered a large area. As a result of this carbonizing burning with excess hydrocarbons, according to the hypothesis suggested by the SPbU scientists, phosphides were formed out of bedrock phosphates at temperatures as high as 1500 С°. The unique conditions of the large, arid Negev Desert made it possible for these phosphides to survive to our times and become an object of scientific investigation.

Why did the land burn? “There was some unidentified, unknown factor... The Bible says that fire fell from the sky. The ancient people had quite possibly seen those huge fires and now, in their ancient books, we find an indirect proof that the source of those fires had been the meteorites,” Britvin said.

When asked by the journalists if their hypothesis was perhaps too simple to reflect the reality, Prof. Krivovichev explained that the theory explaining the origin of life was actually quite complex. All that they suggested was an explanation for one of its aspects — the sources of prebiotic phosphorus.

 

New minerals

The paper about phosphides found in terrestrial bedrock was published in Scientific Reports in February (see doi:10.1038/srep08355). It was written by the heroes of our story — S. Britvin, M. Murashko, and S. Krivovichev, as well as Yu. Polekhovsky (he studied the optical properties of the newly found minerals) from SPbU and Evgeny Vapnik from Ben-Gurion University in Israel. Their hypothesis explaining the origins of Archean prebiotic phosphorus in terrestrial conditions excited the curiosity of the journal’s reviewers — judging by the questions that the authors of the paper had to answer before the publication, these were all accomplished scientists. There have not been any responses from colleagues yet. By scientific standards, papers on this topic can appear within a year after publication (other scientists need to collect the material, carry out their own research in order to present the results in journals or at conferences).

The discoverers of minerals have to right to name them. One of the five new phosphides got the name of murashkoite (after M. Murashko). The others were named after the places where they were found: negevite (the Negev Desert), zuktamrurite (Zuk Tamrur cliff on the shores of the Dead Sea), halamishite (the dry bed of the River Halamish), and transjordanite (Transjordan Plateau)... Minerals with the names britvinite and krivovichevite — after the SPbU crystallographers, also exist. Forty seven minerals altogether have been named after graduates and employees of our University (see http://spbu.ru/podrobnosti/22287-universitet-dostoin-knigi-rekordov-ginnessa).

 

Evgeny GOLUBEV