Atmospheric Gases over the Eons

The “experiment” that humanity has undertaken in our era of fossil fuels

As my readers know, my work is comprehensive in nature, and I have written about my studies in paleology (1, 2, 3), which means Earth’s distant past. That includes how Earth and the solar system formed, so my work looks way back. The Moon is thought to have formed by a collision of early Earth with something Mars-sized, during that hellish eon called the Hadean. Today, it seems that life began on Earth as soon as it could, maybe over four billion years ago. Earth seems to have been a water planet early on, and the atmosphere was mostly carbon dioxide, like Venus’s is today. But because Earth retained its water, it helped set in motion dynamics called plate tectonics today, and the continents soon began forming.

Nick Lane’s work on early life on Earth is enthralling, and it is all about energy, of course. When I update my big essay, among the sources will be Peter Ward’s and Joe Kirschvink’s book on the history of Earth. I think of it as their new book, but it was published over ten years ago. It has been nearly 20 years since Ward published his book on oxygen levels over the eon of complex life, and I reproduced one of his graphics, which led to an amazing exchange. That graphic came from the work of Robert Berner, who pioneered attempts to estimate the oxygen and carbon-dioxide levels in Earth’s past, especially during the eon of complex life.

There is a great amount of research and scientific debate on these subjects, and I am going to sketch some of the highlights of these fascinating – and relevant – subjects. Lane’s idea, that life began in volcanic vents on the ocean floor, seems to be the leading hypothesis, if life began indigenously (not seeded here from Mars, ETs, etc.). The earliest life took advantage of the potential energy in chemicals, wringing the energy from them. But it did not take very long before life began capturing photons, maybe even from the glow of those volcanic vents. But the most important event, after the appearance of life itself, was likely when a photosynthesizer evolved to split water to get its electrons for photosynthesis, which is not an easy trick. Oxygen was the byproduct. Oxygenic photosynthesis might be over three billion years old, and it saved Earth’s ocean from being blasted into space, as Mars’s was.

Some compounds cannot form in the presence of oxygen, and some need oxygen to form. I recently related an example of why scientists know that radioactive-dating methods are accurate. Geologists have discovered deposits that could not have formed with an oxygenated atmosphere, deposits that needed oxygen, and before about 2.5 billion years ago, there is no evidence of oxygen in the atmosphere. Then Earth got oxygenated, and oxygenic photosynthesizers comprise the only significant candidate to cause that. That oxygen also enabled a key evolutionary event that led to animals: oxygenic (AKA “aerobic”) respiration. Aerobic respiration generates several times more energy than other forms of respiration, making multicellular life possible.

To this day, there are lively scientific debates on the oxygen levels during the eon of complex life, and here is a recent paper on the topic. There is great controversy over when oxygen levels rose high enough to allow for animals, allowed animals to come on land, what effect the world’s first forests had, and other fascinating topics. Here is another relatively recent paper on modeling the oxygen and carbon-dioxide levels. In just about all models, there is an oxygen spike in the Carboniferous, up to 35% of the atmosphere. It is thought that the world’s first forests caused that spike, as well as the burial of carbon, which led to most of the coal deposits that humanity burns with such abandon today. That burial had a big impact on the carbon cycle and likely drew down the atmosphere’s carbon-dioxide levels so far that it led to an ice age. Glaciers drag rocks across rocks, leaving grooves in bedrock, and that is a key piece of evidence for the past ice ages. Over the eon of complex life, Antarctica (and Gondwana, which is Antarctica’s parent) has always been near the South Pole, and that is where the three ice ages in the eon of complex life began, including the one that we are in today.

With paleomagnetics and other evidence, scientists have reconstructed the positions and movements of the continents over the eon of complex life, which has alternated between hot periods and ice ages. Scientists have dated tremendous volcanic eruptions, especially beginning when the supercontinent Pangea began breaking up over 250 million years ago, and the reign of the dinosaurs happened during a 200-million-year hot period. Volcanoes belch out carbon dioxide, and all scientists, except those who work for oil companies, accept that those volcanoes and their attendant carbon dioxide are what made Earth so warm then. When Earth was warm, forests extended nearly to the poles, and in ice ages, the poles were the first to get covered in ice. There are very robust, converging lines of evidence (consilience) to establish these scenarios. There is still plenty of debate over them, but no credible paleologist disputes those basics.

After that bolide cleared the continents of non-avian dinosaurs, it marked the rise of mammals, who were previously fringe-dwellers, largely living in burrows and coming out at night to feed, as dinosaurs ruled the day. There was another temperature spike, about 55 million years ago, likely from volcanism, and alligators lived in Greenland in those days of paradise. About 50 million years ago the party began to end, and with little variation, Earth has cooled since then into today’s ice age. Declining carbon-dioxide levels, from reduced volcanism and likely increased weathering from the new Himalayas and other mountains, is thought to have been the primary cause of this ice age. Another piece of consilient evidence is that about 32-to-25 million years ago, some plants evolved a new method of photosynthesis that conserved carbon. Today, grasses are the most common users of that new method, and grasslands spread in that cooling, drying world.

The basics of what I presented above are not disputed by any paleologists that I know of. The debates are over oxygen and carbon-dioxide levels and key life events, but the basics of ice ages, warm periods, and carbon-dioxide levels are not seriously disputed. That is what makes today’s “debates” over Global Warming so ludicrous. Human activities, namely the burning of hydrocarbon fuels that power industrial societies, have increased carbon-dioxide levels by 50% in the past 150 years. Nothing that dramatic has happened in the journey of life on Earth, and it is either idiotic or dishonest to argue that it will have little or no impact. The so-called debate was phony from the beginning, when Fred Singer led the charge on behalf of the oil companies in the early 1990s, to create the illusion of uncertainly over carbon-dioxide’s role in Earth’s climate. There was not any uncertainty by climate scientists or paleologists that increasing the carbon-dioxide levels would warm Earth’s surface. The only debate was by how much and how fast, but Arrhenius’s calculations from the 1800s are still the relevant ones. And I don’t need scientists to tell me that, as I have been witnessing the dramatic warming in my home state since the 1990s, as the glaciers quickly melt, we have had record-shattering heat waves in the past generation, and over the past decade, the forest fires have gotten so bad that in the summer I now have to check both the weather and smoke forecast before I go hiking.

Humanity is performing a great “experiment” with Earth’s atmosphere and climate. We may have already ended this ice age, and a warmer planet is not necessarily a bad thing. The problem is the rate of change, which is already overwhelming the ability of species to adapt. What is called “extreme weather” is on the rise, and there will be epic floods, droughts, and crop failures while billions of people will starve, which could lead to nuclear war. That is the biggest risk that we face.

I know how to end the threat forever, but I can’t do it alone.