Victor Luca, 14-Jan-21
The best science we have is telling us that planet Earth formed about 4.54 billion years ago. We can measure the date using isotopes (206Pb/238U ratios) present in minerals of rocks that have been found on the surface of the Earth.
Photograph of Jack Hills Zircon (chemical formula ZrSiO4) dated at 4.4 billion years old. Source: Oskin, B., Oldest Fragment of Early Earth is 4.4 Billion Years Old.
To start off with the new planet Earth was pretty inhospitable to what we have come to know as life. That is, life based on the chemistry of carbon. A fundamental requirement for life as we know it is water and in the beginning there wasn’t any. There are different theories for how water came to be on our planet in the first place. However, the theory currently considered most plausible is that the first water came from asteroids. The human body is mostly comprised of water and for chemical reactions based on carbon to occur, water is an absolute prerequisite. In chemical jargon water is often referred as a ‘universal solvent’. Once there was some water on Earth, then carbon-based life could begin to flourish in earnest.
For 99.9% of the 4.54 billion years of the Earth’s history, recognizable humanoid life hadn’t even appeared. Organic life would have initially taken the form of very simple organisms, probably something like bacteria and viruses. The latter are perhaps not even strictly speaking alive. In fact, we now know that all extant living creatures derived from a single common ancestor, coincidentally referred to as LUCA, for the Last Universal Common Ancestor. LUCA was a simple prokaryotic creature (a single-celled bacterium with unprotected genetic material) that lived some 3 billion years ago. It must have been a very tough organism to have survived in the early Earth’s very extreme environments.
The first signs of these single-celled organisms appear around one billion years after Earth’s formation. These would have increased in complexity as the molecular building blocks became more abundant and more diversified. One theory of life refers to the primordial soup and invokes the action of lightning on the gases that most likely constituted the primitive atmosphere with the resultant molecules condensing in shallow pools of water (the soup). This is known as the Miller hypothesis because it was Stanley Miller and Harold Urey that in 1953 demonstrated that you could take a closed flask containing simple molecules such water (H2O), methane (CH4), ammonia (NH3) and hydrogen (H2) and apply an electric discharge and generate all 20 of the amino acids that constitute DNA. These and other amino acids constitute the building blocks of proteins which are basically what we are made of.
Other theories for the origin of life on Earth include the theory of Panspermia which has it that life hitched a ride on space objects such as asteroids and comets which reached Earth from the depths of space. Indeed, there is some support for this theory because we have identified amino acids on remnants of meteorites known as carbonaceous condrites that have struck Earth in the past.
Organic life was well and truly flourishing when the first humanoid life appeared on the scene in the form of a creature dubbed Australopithecus back about 5 million years ago (0.005 billion years). It took many millions of years and lots of evolution for homo sapiens to finally turn up about 35,000 years ago. Humans today have inherited an Earth teeming with life. Theory has it that when our primate ancestors descended from the trees and started walking upright, they simultaneously got smarter and learned how to use their hands better and make tools that could be used to make other things.
Modern humans learned how to gather and cultivate crops only about 11,000 years ago when the number on the planet was only about one million. Then, for many years, the numbers of humans increased slowly. We learned to communicate both orally and later in written form, and over time, we developed to the point of being able to manufacture complex objects and machines.
In due course we learned how nature works, about the elements, how to build molecules by design, about how our bodies function and how to look inside them and fix things. We learned to see the world through math, physics, chemistry and biology and we discovered all manner of things about the natural and physical world around us. We invented the wheel, the steam engine and railways, writing and the printing press, electricity and many many other things. These inventions and others sparked an industrial revolution which magnified our numbers exponentially starting from about the middle of the 18th century. We became the most successful animal on the planet by far and we even began to venture into outer space. Of course I use the word ‘successful’ advisedly as it depends on your definition of success. If we define success in terms of sheer numbers then, ants far outweigh us in terms of biomass - billions and billions of tons for ants versus about 500 million tons for humans. If we define success in terms of our ability to destroy everything, then we are clear winners.
We humans have been to the moon and sent our machines (space probes) to the outer reaches of our solar system, as far as Neptune in fact. We invented telescopes of all types to see way beyond where we can send our probes and microscopes that can see things close up, almost the size of an atom.
As we have gotten smarter and more numerous, we have turned our world upside-down and inside-out. Our obsession with burning fossil fuels has changed, and will continue to change our planet’s atmosphere for some time to come even, if we stopped burning stuff tomorrow. There is not a corner of the globe that we have not ventured into and despoiled.
We are by far the most ‘successful’ predatory animal in the history of Earth and perhaps the most destructive.
However, as we become more successful we are also posing an increasing risk to the well being of every other creature with which we share this Earth, including ourselves.
About 16 years ago I gave a presentation to executive managers and external reviewers of the organization I was working for at the time, The Australian Nuclear Science and Technology Organization. These types of reviews were an essential final step in the process of obtaining government funding for research projects.
My graphic depicted the linear increase in atmospheric CO2 concentrations between 1984 and 2003 measured at Cape Grim in Tasmania, Australia (a). The consequence of this is the Greenhouse effect (b) which would lead to global warming (c) which would then have consequences such as loss of sea and land ice (d) which would beget sea level rise. The final consequence would be extinction of species (e).
It is hard to believe that almost two decades have passed since I gave this presentation and during these entire two decades, and amidst shrill cries from the scientific community, scant progress has been made in arresting emissions and limiting the extinction of species. This was shown by the cover of a 2004 issue of Nature magazine in which the feature article concerned the loss of biodiversity. The authors of the article calculated the rate of species extinction under various climate change scenarios.
The abstract to the paper contained the following dire statement. “We predict, on the basis of mid-range climate-warming scenarios for 2050, that 15–37% of species in our sample of regions and taxa will be ‘committed to extinction’”.
The authors went on to state. “These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.”
Today, a decade and a half later, in the epoch known as the holocene, we talk about the sixth mass extinction or Anthropocene extinction and it is occurring before our very eyes.
Recently a paper was published in another prestigious science journal, Proceedings of the National Academy of Sciences, by Ceballos et al. in which the authors made the point that during the past 450 million years there have been five mass extinctions that were caused by abrupt and catastrophic alterations in the environment. One of these mass extinction events extinguished the dinosaurs. This occurred toward the end of the cretaceous period about 65 million years ago. We know these creatures existed because we have found their bones everywhere and we can date them reasonably well. Other types of life came back and flourished, but the unique dinosaurs, once gone, would never return although we are surrounded by their descendants, the birds. The same is true of every species that is rendered extinct, once gone, they are gone forever.
When species become extinct they disappear together with the unique ecosystem services that they provide us humans. We humans rely on these many ecosystem services and without them we are done for.
The figure below taken from the recent paper by Ceballos et al., gives us a glimpse of where we are heading and it is not pretty.
Population size of terrestrial vertebrate species on the brink (i.e., with under 1,000 individuals). Most of these species are especially close to extinction because they consist of fewer than 250 individuals. In most cases, those few individuals are scattered through several small populations.
It took billions of years of evolution to produce complex organic life like humans from LUCA and we are now in jeopardy of extinguishing it in an instant.
It was Darwin who first coined the expression “Survival of the fittest”. So far we humans are looking pretty fit but for how long and at what cost? Perhaps someone should write a sequel to Darwin’s book and entitled it “On The Origin and Extinction of Species”.
So far in NZ we have done a lot of talking about climate but unfortunately, like many other developed countries, the rhetoric has not been matched by action. Indeed, recently we were given a slap in the chops when we were left out of the Climate Leaders Summit.
Ceballos et al., Vertebrates on the brink as indicators of biological annihilation and the sixth mass extinction. PNAS 2020,117(24), 13596.
Chappell, B. 7 Billion And Counting - Along With Humans, Who Else Is In The 7 Billion Club? 3-Nov-11.
Glaiser, M. The Microbial Eve: Our Oldest Ancestors Were Single-Celled Organisms. January 31, 2018.
Koebler, J. The Simplest Living Organism Ever Has 437 Genes and Was Made in a Laboratory.
Libby, E. Ratcliff, W.C. Ratcheting the evolution of multicellularity. Science 2014, 346(6208), 426-427. DOI: 10.1126/science.1262053
Stierwalt, E.E.S. How Did Water Get on Earth? Scientific American, 6-Oct-2019
Thomas et al., Extinction risk from climate change. Nature 2004, 427, 145-148.