Australian scientists have found that the first genetic change after the formation of life occurred a billion years before the date that was accepted until now: it is a genetic leap, adapting prokaryotes (without a nucleus) to eukaryotic cells (with a nucleus), which make up all living things today except bacteria
Last week a headline was published announcing that life on Earth began a billion years earlier than previously thought. Since the accepted date for the beginning of life is about 3.8 billion years ago, if we accept the title as simple - life began before the formation of the earth, 4.5 billion years ago. But further delving into the information settles the contradiction and reveals that it is about advancing the clock to a certain intermediate stage in the development of life, and not to the phenomenon of life as a whole.
What are those forms of life that have been published in the world's newspapers? And what's the big deal about them being "slightly" older? The news talks about single-celled creatures and their name is eukaryotes. One would think that these are exotic animals that have already passed away from the world. But reading between the lines reveals that we, humans, are also among these eukaryotes, and in fact all visible life on earth belongs to this kingdom: grasshoppers and beetles, snails and slugs, carobs and lilies, cats and partridges. Some of the single cells we encounter in our daily life, yeast used in baking and amoebas that invade the intestines, are also eukaryotes. Only the bacteria of their kind belong to other animal kingdoms, the prokaryotes and the archaea. The viruses, which are not real living beings, are not included in this division.
The root of the above strange terms is the Greek word kryon, which means nucleus. Indeed, all eukaryotic organisms are made up of cells at the heart of which is a true nucleus. Inside the nucleus are the chromosomes - those "volumes" of the genetic encyclopedia, in which the hereditary information that characterizes each and every creature is "written". The prokaryotic (pre-nuclear) bacteria do not have a cell nucleus, their genetic information is sparser, and it floats around the cell in no clear order.
But this is not where the differences end; Eukaryotic cells are much larger and more sophisticated than prokaryotic cells. Their volume is about a thousand times larger, and within them are organelles (subcellular organs), the size of each of which is the size of a bacterium. With the help of an electron microscope, you can see that the organelles are surrounded by fatty membranes of a similar type to the one around the whole cell. One of the types of organelles is the mitochondria - tiny chemical factories that break down sugars from food and use them to produce the chemical substance ATP - the universal energy currency of the living cell. Other organelles are responsible for the production of proteins or the chemical use of light energy in plants (photosynthesis).
The transition from prokaryotes to eukaryotes is thought to have been the first genetic upheaval since the origin of life. In contrast to the gradualism that emerges from the word evolution, it seems that the perfection of life on earth often occurred precisely in the style of revolution. The eukaryote revolution was a process in which the importance of cooperation, or symbiosis, was discovered. Lynn Margolis, an evolution researcher from Boston University in the USA, was the first to propose the innovative idea that the organelles found inside eukaryotic cells were originally independent creatures. According to this theory, which is now widely accepted, the coming together of several types of bacteria-like creatures made possible an important leap, which eventually led to the appearance of man.
Until recently it was widely believed that the eukaryotic revolution happened less than two billion years ago. This indicates that the era in which the bacteria ruled outside of Egypt lasted close to two billion years, about half the total duration of the existence of life on our planet. It seemed to many of the scientists that this long period of rule left too little time for all the other revolutions that followed, revolutions that made possible the appearance of complex multicellular organisms. The new study, which appeared a few days ago in the important scientific newspaper "Science", cuts about a billion years from the "Stone Age" of life. This left a much larger scope for the intriguing evolutionary processes that took place later, including the appearance of differentiation (different cells for different organs) and mating (the male and female sexes). All of these played a central role in the development of living beings. How did the Australian scientists who published the article arrive at their far-reaching discovery?
As in many other cases, the scientists feed on small hints, which could easily have disappeared from the eyes of any other person. They make sure to clarify the route they took to allow other researchers to confirm or refute their conclusions, and describe in detail the control experiments that prove that this is not a mistake. They even emphasize the possibility that their conclusions will ultimately prove to be only partially correct. This cautious approach is what characterizes science versus pseudo-science, when in the latter the details of the experiment are often missing, and the conclusions are sounded as indisputable. The scientists studied the chemistry of rocks brought up by drilling from a depth of about 700 meters from layers whose age has long been dated: they were formed 2.7 billion years ago. The rocks found are of the bitumen type - a mineral that contains hydrocarbon substances similar to crude oil. The researchers carefully chose the drilling site in northwestern Australia; This layer of rocks suffered less in the years of its long existence from extreme pressure and heat phenomena. It was already known before that such rocks contain many different organic substances, and even tiny fossils of single-celled creatures. But the identity of the fossils was in doubt: are they prokaryotes or eukaryotes?
Due to the degree of preservation of the rocks removed from the drilling, it was possible for the first time to make a reliable analysis of organic substances in a rock of such an advanced age. The oldest rock studied so far in a similar way was 1.6 billion years old. In the 2.7 billion-year-old layer, lipids were discovered, fatty substances consisting mainly of carbon and hydrogen and similar to those that make up cell membranes today. The chemical "fingerprint" of the substances made it possible to conclude that the original cells from which the fats remained were of the eukaryote type. The most important finding that enabled the scientific breakthrough was a cholesterol-like substance, an essential component of eukaryotic cells, which is hardly found in prokaryotic cell membranes. It is important to note that in such studies it is not possible to use the analyzes of more acceptable living substances such as DNA or proteins, since these decompose completely in a relatively short time.
The new study is presented as an important first step on a long road. It strengthens the basis of a relatively new scientific branch, chemical paleontology. It is a combination of observation of the shape of the single-celled fossils with their detailed chemical analyses. This path holds a promise: to decipher not only the first genetic transformation, but also the secret of the existence of life in general. It is possible that within a few decades, in combination with other approaches such as advanced organic chemistry, genome research, computational biology and bioastronomy, we will finally be able to answer one of the great riddles of science: how, throughout the ancient ocean, the first living cells were formed from a "dead" collection of chemical substances.
