How life controls Earth — and how it originated (at least) 3.7 billion years ago
Interview with Professor of Geology Dr Minik Rosing
When did life arise? Professor Dr Minik Rosing has an answer, and it comes with some remarkable implications: Not only is life significantly older than we believed just a couple of decades ago, but it also exercises a large degree of control over our planet’s atmosphere and continents. This assumption goes against our common-sense perception that it is the unique and favourable conditions on Earth that have supported the spread of life since its inception. It means that we will in general have to change our view of cause and effect in understanding the creation of our existence.
Minik Rosing is undoubtedly Denmark’s most influential geologist, and a part of the geological world elite. His roots lie in Greenland, which is where his father’s family comes from. Greenland is also important in the world of geology, since our scientific understanding of the Earth to a large degree stems from geological examinations of this autonomous country within the Danish Commonwealth, which in addition to being the world’s largest island also has the world’s oldest contiguous complex of rocks.
The reader should particularly take note of the name Isua. It was here, in the late 1990s, that Minik Rosing found the rock material in which he was able to detect carbon traces of the oldest known form of life: microorganisms at least 3,700 million years old. This important discovery has subsequently been the springboard for a range of remarkable theories about early life and the continents of our planet — and they all bear Rosing’s signature.
What is ‘life’?
I had two rounds of interviews with Professor Rosing; the last in his historic and beautiful office in the University of Copenhagen’s Geological Museum. In this article I will present his theories and ideas. But first, I would ask readers to refresh their own basic knowledge about life itself:
The Earth is 4,567 million years old. Life has probably arisen just once on our planet, and the last time it happened was for sure at least 3,700 million years ago. Since then, life has kept running in one unbroken chain, where the living has reproduced itself. This means that spontaneous genesis isn’t happening all the time. Mould, for example, doesn’t grow spontaneously on old bread, but derives from existing fungal spores that float in the air and obtain nourishment for their reproduction when they land on the bread. In other words: Life comes from the living. We have known this since the time of Louis Pasteur. It also means that there are parent generations for all life; Charles Darwin demonstrated this, and science has since confirmed and strengthened his thesis. As a consequence, everything we can identify as being alive can be traced back to a common point in the past, if we can trace the chain back far enough. Everything alive is therefore related — from the smallest bacteria under our fingernails to the potted plants on our windowsill and the very largest animals. All of this life is organised in three domains with six subordinate kingdoms in a single, connected family tree with a sin gle root, which modern molecular biologists call LUCA: the Last Common Universal Ancestor. Human beings like us, Homo Sapiens, are just one species of organism among unimaginably many others, and all species arose from the same basic form an incredibly long time ago.
Since life arose, it has developed through evolution over thousands of millions of years, and can hence be seen as a perpetual motion machine that has kept moving by constantly procreating and adapting. Through this, it has defied the second law of thermodynamics — the basic law of the universe — which says that over time, all order will sink into disorder (increasing entropy), and that any machine or chemical process will grind to a halt because of some sort of friction with its surroundings.
Yet so far, this hasn’t been the case with life. We are here. We are alive — and we are all characterised by our ability to metabolise (convert energy), procreate, evolve in reaction to our environment, and preserve hereditary information (DNA) that we pass on to future generations.
We are thus all part of the great machine of life, and it is this machine — life itself — and its origin and influence over our planet that is the focus of Professor Rosing’s research. Rosing may not be a biologist, but ancient mountains tell the origin story of life through sedimentary deposits of carbon from single-celled organisms, which are visible as tiny, coloured lines if you find the right rocks.
Observation of 3,700-million-year-old life
Professor Rosing specialises in a branch of geology called petrology, which is the study of how rocks form; petros is Greek for rock and stone. He is particularly interested in the sub-branch of metamorphic petrology, which deals with the processes in the planet’s crust that generate new types of rock from, for example, lava, chalk, clay and granite.
We know the word metamorphosis from other contexts. It, too, is Greek and means change, transformation, conversion and reformation. As such it is not a specialised geological term, but in geology, it is used when external circumstances in geological processes change, causing the minerals in a rock to reform or react with other minerals. In metamorphosis, chemical reactions take place between the mineral grains of the original rock, creating new minerals. The grains change their size and shape, giving the new rock a different appearance from the parent rock.
A central trait of all life is that it is built up from organic compounds, all of which are based on carbon. In living things, the carbon is usually bound to hydrogen, nitrogen, and phosphorus, while in non-living things it is bound to oxygen. Free carbon is hence a good sign of early life in rocky material — though this presupposes that it can be proved that the carbon in the rock is as old as the rock itself and hasn’t, for example, entered through cracks or fissures at a later time.
For this reason, geologists operate with two concepts relating to the material they work with in their quest for early life: biogenecity, which is about showing signs of early life (biological origin), and syngenecity, which is about demonstrating that the biogenetic material is as old as the rocky material in which it has been found.
“If both conditions are met, research results are taken seriously as a true observation. Singular observations are not enough,” Rosing tells me.
The most difficult part is demonstrating syngenecity, and throughout the 20th century, the supposition was that life was most likely no older than 3,500 million years. This is because the Moon — and hence probably also the Earth — was subjected to intense bombardment by meteors from about 4,000 to 3,700 million years ago. Since the Earth is larger than the Moon, the number of impacts on the Earth would also be greater, and the effect of this so-called Late heavy bombardment ought to have been a totally sterilised Earth. This means that Earth could not begin to develop the conditions for life — and later, life itself — until after the end of the bombardment, which was thought to have lasted for a few hundred million years.
Yet in 1999, Professor Rosing demonstrated something else.
In a rock sample from Isua that with certainty was at least 3,700 million years old, he found carbon from prehistoric life in the sedimentary structure — a graded layering, with thicknesses of a few millimetres and upwards. Isua, situated north-east of Nuuk in Greenland, has been the epicentre of world-level geological research for the past half century, because it holds the most ancient continuous complex of rocks: They are 3,800 million years old.
“This carbon is formed from thousands or millions of years of dead organisms falling to the sea floor in a light sprinkling, which over time together with clay forms slate,” he explains.
With this discovery, published in the prestigious journal Science, he had solid evidence of both biogenecity and syngenecity, and hence a real sensation on his hands: in a single stroke, the earliest signs of life were pushed 200 million years back in time.
In 2017, Rosing again published results from Isua with the same conclusion, on this occasion in the journal Nature, with his colleague Tue Hassenkam as the main author. This time the test subject was a garnet from the Greenland massif, and once again the results pointed to life that was at least 3,700 million years old. This study thus confirmed Rosing’s earlier findings.
“This time, however, we used more recent techniques for the analysis and had better equipment, which provided far better certainty of the precision of the results. We saw that nitrogen, oxygen and phosphorus were still bound to the carbon in a way that said that the original material must have been made up of biological molecules,” he says.
Photosynthesis is older than originally thought
What is spectacular about Professor Rosing’s finding is not just the age of the biogenic material — just as interesting is his subsequent idea that the original organisms possessed some form of photosynthetic capacity, i.e. that they harvested energy from the sun.
“These must have been fairly advanced organisms, for example a type of bacteria that lived in open water in the uppermost water layer, and which was able to make use of the solar radiation that oxygenated the water. I am convinced that the high carbon content in the sediment best can be explained by living organisms at this time having developed a metabolic strategy that allowed them to utilise solar energy,” he says.
This in turn means that photosynthesis is an invention more than 3,700 million years old. But why is this so important?
“The really smart thing about this invention is that the organisms can pool photons (particles of light — ed.). The energy of a single photon of sunlight is not quite high enough to do anything — such as splitting water into oxygen and hydrogen. But with photosynthesis, an organism can store energy, in the sense that through pigments it can take the energy from several photons and combine it. This energy is enough to cleave H₂O, binding the hydrogen to a carbon dioxide molecule, while also releasing a lot of oxygen. This in turn means that you can create an atmosphere with oxygen in it,” Professor Rosing explains:
“An alternative might be that the earliest life on Earth fed solely on the chemical energy welling up from inside the Earth — which is a small fraction of the heat flow. We know this number with reasonable certainty: about 0.1 watts per square metre. Still, it would be a very boring form of life that could evolve from this miniscule amount of energy.”
This is why photosynthesis is so important, including the time when it arose. It is simply the prerequisite for life to be able to evolve into the complex, advanced lifeforms of our time:
“Through photosynthesis, the organisms’ access to energy was increased by orders of magnitude,” says Rosing.
Life has created and controls our atmosphere
We tend to believe that conditions on Earth were optimal for life from the beginning, but this is only partly true. The distance from the Sun was right from the start, and the tilt of the Earth’s rotation relative to its orbit around the Sun was also favourable. This helped to distribute the sunlight across the globe, with appropriate heat levels.
“However, the Earth’s atmosphere isn’t static,” Rosing explains. “Our current atmosphere consists of 78% nitrogen, 21% oxygen, 0.9% argon, 0.04% CO₂ and some water vapour that varies with temperature. All of the oxygen is produced by plants and microorganisms, through photosynthesis.”
In other words, 21% of our atmosphere wasn’t there on the young Earth before life arose –while CO₂ levels, on the other hand, must have been far higher, as we also know that the Sun’s energy was significantly weaker 2,000–3,000 million years ago. In fact, the CO₂ content must have been upwards of 1,000 times higher, or 40%.
Unless, of course, there is an entirely different explanation — which Rosing thinks is the case. After all, his research shows that life existed as early as 3,700 million years ago, but that would not have been possible with so much CO₂ in the atmosphere. So how does this work?
Rosing has shown that the CO₂ level 3,500 million years ago could not have been much higher than it is today:
“It wasn’t an extreme greenhouse effect that made it possible for the Earth to keep warm. Instead, the explanation may be found in the fact that the early Earth, without continents but with a global ocean, radiated less of the Sun’s light back into space than is the case with our present-day Earth with its continents,” he says.
Given this, he also thinks that the continents came into being later than is generally assumed.
While continents reflect roughly half the sunlight, the oceans reflect only about 10%. The rest remains on the Earth as heat. This ability to reflect sunlight is called albedo (the degree of whiteness). A perfectly white surface has an albedo of 1, while a totally black surface has an albedo of 0.
“One consequence of the rise of relatively light-coloured continents was that the Earth’s albedo increased, compared to back when the relatively dark oceans dominated — and for this reason, the heat account was in balance from the beginning, despite a young, weaker sun and despite CO₂ levels being roughly the same as today,” he says.
In other words, the Earth’s albedo has increased at roughly the same rate as the Sun’s intensity, and the changes have cancelled each other out. Over time, life, through its widely scattered growth, has formed our present-day atmosphere with its high oxygen concentration of 21%, which overall creates the optimal conditions for life.
The Earth’s atmosphere covers the entire planet and, not unlike the glass roof of a greenhouse, functions as an insulating layer that retains solar heat while letting sunlight pass through to warm us. This is why the Earth’s average temperature is 15°C, which makes life possible. Without the greenhouse effect, the average temperature would be significantly lower, and we would speak of negative rather than positive degrees. The atmosphere also protects life on Earth by, for example, absorbing the Sun’s ultraviolet rays and by reducing the temperature gradient between day and night, as well as between different regions on the planet. This is primarily done by transporting and distributing large amounts of water.
In other words, the atmosphere is a stabilising system conducive to life, bringing stability to all life on our planet, and it also a (co-)creator of life itself, just as life controls its balance.
Life created the Earth’s continents
Life, however, hasn’t just created our protective atmosphere, which wraps all the way around the Earth; life has also had an important influence on the Earth’s lithosphere — the outer, approximately 100 km of solid ground, Rosing thinks.
The lithosphere consists of the Earth’s crust (the upper 10–70 km of ground) and the upper part of the mantle, and it is divided into tectonic plates that slide across the soft, underlying asthenosphere.
The fact that the continents are moving is relatively new knowledge. The German polar explorer and geologist Alfred Wegener posited the theory of continental drift in 1912, but it wasn’t generally accepted until 1966. Today, plate tectonics is the grand unifying theory of geology, and most of geological research (about climate, landscapes and minerals) relates to it in one way or another.
The implication of Rosing’s theories is that 4,000 million years ago, the Earth was covered with water, with no continents. His idea is that the energy needed to form the continents came from the quadrupling of energy that was made possible by organic photosynthesis. Photosynthesis contributes 0.3 watts per square metre, while chemical energy from within the Earth is 0.1 watts per square metre.
“Seen this way, it becomes clear that life contributes three times as much energy to geological processes as the energy from the Earth’s interior, which we normally see as the geological driver,” Rosing says, and sums up his theories:
“If it is true that the early Earth had oceans almost from the beginning, it is likely that life arose equally early — and hence it is also likely that evolution gave rise to photosynthetic microbes. These microbes, as they spread through the oceans, delivered free energy to weather the basalt in the unstable crust.”
Weathering of basalt is a process in which minerals are broken down in reaction with water or atmospheric gases. Basalt is a dark, heavy rock formed when magma from inside the Earth solidifies. The ocean bed mainly consists of basalt, and all the rocky planets in our solar system and our Moon have basalt crusts. It is a very common rock — but granite isn’t. It is found only on Earth, where it covers a third of the surface, in a layer just 20–30 kilometres thick.
“Weathering is a crucial part of the chain of processes that result in the formation of granite — and granite, in turn, is essential in building continents. Granite is too light to sink into the softer underlying layer, so it accumulates in the Earth’s crust. The interesting thing is that only the Earth has granite, which supports the chain of theories we have talked about today, where photosynthetic life created granite, which created continents,” Rosing concludes.
As the example of Alfred Wegener and his theory of continental drift has shown us, it can take quite a while before a new, radical theory gains recognition. In Wegener’s case, it took half a century.
How long Rosing must wait for the stamp of approval from the geological community at large, we cannot know. Still, his theory is a candidate for the greatest breakthrough in understanding the Earth’s development since Wegener.
The future for the exploration of the origin of life — and for Minik Rosing
Minik Rosing’s expert knowledge is often called upon when the search for the origins of life is being explained. Most recently, he was consulted as an authority on Danish national television when NASA’s Perseverance rover touched down on the surface of Mars in February 2021.
I asked him where he thinks we will one day find the origin of life. Will it be on Earth or somewhere else in space, such as Mars?
“It could easily be outside the Earth, for example on Mars. It will at least be somewhere where there has been liquid water. But I’m not so concerned with where life originated, because when we’re looking for it elsewhere than on Earth, we’re just exporting the problem, in a way. If we find traces of life on Mars, then we must ask: How did it originate there? The problem is the same, and the origin of life will still be enigmatic.”
He himself believes that life arises as soon as the conditions are present. It is not a process that waits, because there is no saving or accumulation of the conditions that make life possible.
“When the conditions are present, they are present, and then we must expect life to arise,” he argues.
But if photosynthesis was possible as early as 3,700 million years ago, there may have been a more primitive form of life before that. I ask him to go from certain knowledge through observations to speculation: When does he think life originated on Earth?
“I think life may have originated between 4,300 and 4,000 million years ago. I simply cannot see why it should have waited,” he says.
I ask him about his own grand theory that unites early life on Earth with the formation of the atmosphere and the rise of the continents. When will this theory get the blue stamp of approval from the entire geological community? Will he and his theory have to wait for as long as Alfred Wegener’s theory of continental drift?
“It’s not certain that the theory will ever get the blue stamp. There are different schools in geology. One of them still believes that the continents were there almost from the beginning. I can’t say that I am sure that the theory is properly described in all areas at present. But on the other hand, I’m quite sure that it’s not entirely wrong either. So time will tell to what extent the theory will stand for posterity,” he explains modestly.
And what about Minik Rosing’s own future — what does it offer?
The Professor jumps up, and from a corner of his office, he picks up a flat cardboard box containing something that looks like abrasive dust or cement. It is not that, but on the contrary glacial rock flour from Greenland.
“My immediate future involves this grey material, which is found everywhere in Greenland. We are doing an experiment with the Novo Nordisk Foundation to see if it can be used for something sensible,” he says.
“The glacial rock flour formed over millions of years when the great ice caps and glaciers ploughed through the land and pushed away the decomposed and nutrient-depleted minerals. Instead, the ice deposited soils full of newly crushed rocks from the bedrock. All of these minerals retain their nutrients, and because they are powdered by the ice, their surfaces are freely accessible to plants, fungi and bacteria in the soil, which can release the nutrients,” he explains, and continues:
“The idea is to transport this glacial material to places in the world where the soil is depleted and use it as a kind of fertilizer — and we have already performed experiments in which the cultivation of the soil has yielded significantly better results. The nutrients found in the glacier flour are lacking in tropical soils. That’s the reason why large areas of tropical rainforest are burned every year — so that the small amounts of nutrients found in the trees can be released to the depleted soil. If we are right in our assumptions about the properties of glacier flour, it will be possible to avoid having to burn the rainforest, because the soil can instead be fertilized with the flour.”
But what about the Greenlanders themselves, I want to know — what do they say when their raw materials are exported in this way?
“Unlike many of Greenland’s other raw materials, new rock flour is constantly being formed, and it can be utilized without the risk of polluting the environment. It does not disappear, and there is plenty of it in Greenland,“ he says, and laughs:
“This is part of the Greenland mud, and most people find it annoying to walk around in up there. But no one has ever researched whether glacier flour is an interesting resource that we can use for anything. So if we succeed, we will both have an export product for Greenland and a natural product that can benefit the world.”
