Life is inextricably tied to the climate. Over the four and a half billion years of the Earth’s existence, the climate has changed dramatically, from a planet with no oxygen to one with 35% oxygen to one with today’s level of 20% oxygen. The temperature has also changed, from a planet much warmer than the one we live in today to one frozen solid from pole to pole.
These changes are the result of the motion of the Earth through space, plate tectonics, and the interaction of life with the land, sea, and air. These changes affect the concentration of gases in the atmosphere and nutrients in the oceans which, in turn, determine how life evolves. In other words, it is a feedback loop. The change in the planet affects life and the evolution of life changes the planet.
The process has been anything but smooth. There have been five mass extinctions in the last 500 million years on Earth1. There is considerable speculation about what caused these extinctions. The one that we are most certain about is the fifth or most recent mass extinction, called the Paleogene-Cretaceous Extinction, that occurred 66 million years ago and killed the non-avian dinosaurs.2 It is the most famous one and was most likely caused by the impact of an asteroid the size of Mount Everest which left a crater 110 miles across and 20 miles deep under the Yucatan peninsula in Mexico. However, there is evidence that the dinosaur population was beginning to diminish before that, so the asteroid may have just finished them off.
At least one of the five mass extinctions may have been caused by life itself. The first mass extinction, called the Ordovician Extinction, occurred 445 million years ago. Most of life then was still in the oceans, but plants had begun getting a toehold out of the water. As they spread on land, their roots and tendrils broke up the rock and created soil. Rain washed this soil into the oceans. It contained large amounts of phosphorous, which plants need to grow. This caused an enormous growth of algae in the oceans. Bacteria need oxygen to consume dead plant matter, so as the algae died, the bacteria took large amounts of oxygen out of the water, and this killed 85% of all sea animals.3
But by far the greatest example of life extinguishing life (so far) is the Great Oxygenation Catastrophe. This one isn’t even counted among the five mass extinctions that occurred in the past 500 million years because it occurred 2.5 billion years ago. The reason it isn’t counted is because it occurred before plants and animals, and the mass extinctions refer to the extinction of multicellular organisms. Two and a half billion years ago there were only bacteria – single-celled organisms. .
Two and a half billion years ago, the atmosphere and oceans had no oxygen. The bacteria alive then did not need oxygen to survive. They are called “anerobic” bacteria. Then a new bacterium evolved capable of photosynthesis, which means that it used sunlight and carbon dioxide to make energy and gave off oxygen as a waste product. Over millions of years this oxygen built up in the atmosphere.
Oxygen, as it turned out, was toxic to the anerobic bacteria which then almost went extinct – basically killing all life on Earth except the photosynthesizing bacteria. Today anerobic bacteria survive only in places where oxygen is scarce – on the sea floor or in the guts of animals (including us) where they aid in digestion.
This is another example of life killing life. We are now in the middle of another, similar event. A relatively recent life form, one of the variants of African Apes which we call Homo Sapiens, discovered how to use fossil fuels. This enabled it to greatly expand its population which, in turn, greatly increased its use of fossil fuels in a self-reinforcing cycle.
Somewhat like the photosynthesizing bacteria 2.5 million years ago, the activity of this life form has rapidly increased the concentration of a waste product – in this case, carbon dioxide. The speed at which this has occurred relative to geologic time is instantaneous. Where geologic processes take thousands or millions of years, in just 100 years Homo Sapiens has increased the concentration of carbon dioxide in the atmosphere by 50%. This is so fast that the consequences of this change are trailing the change itself, which is why most of the world is unaware of the dire straits we are in.
This tenacious life form continues to emit this waste product into the atmosphere in ever larger quantities, and the result will be a rapid and dramatic change in the global ecosystem that will result in another mass extinction. This extinction, largely due to the destruction of natural habitat, is already well underway. In the last 50 years, the wildlife population of the planet has plunged by 70%. In Latin America and the Caribbean region, including the Amazon, the drop has been an astonishing 94%. Scientists have already recognized this fact and have called it the Sixth Mass Extinction.
The notion that what is going on is a regular, cyclical process of nature is simply misinformed. Because our personal lives have not yet been seriously disrupted does not mean that the planet has not been.
Homo Sapiens is a clever animal and may find ways to survive the climate disruption it has caused that will radically alter the face of the planet, but it suffers from a weakness. It depends on a complex global infrastructure, and that infrastructure is very vulnerable to disruption by adverse events – droughts, storms, floods, and wildfires – all of which will become more common and more severe as the planet continues to warm. There is no certainty that Homo Sapiens will survive the consequences of its own activities, or, if it does, that it will be in a form that resembles today’s advanced technology.
1 The Earth is 4.5 billion years old. Multicellular life, like animals and plants, have only been around for half a billion years – that’s just 10% of the age of the Earth. For most of the history of the planet, the only life was bacteria.
2 Birds are descended from dinosaurs.
3 An environment low in oxygen is called hypoxic. An environment devoid of oxygen is called anoxic.
4 Carbon dioxide is the main gas that keeps the planet warm. Too little and the planet freezes. Too much and it burns.