Deep Time is a recent concept. As explained in this Wikipedia entry, it was coined by John McPhee in 1981 to apply to geologic time.
The geologic time scale was introduced by James Hutton in the 18th century to refer to the rock record of Earth. Since then modern geologists have extended the scale back to include the formation of the Earth 4.54 billion years ago.
Universe
The Universe’s Big Bang beginnings are estimated by astronomers to have occurred about 13.8 billion years ago. These time scales are very difficult for us to imagine, even today as modern humans, especially given that the average human life span is less than 100 years and modern science is only a few hundred years old. Humans have evolved to live for the moment and normal everyday life planning is normally measured in days or perhaps weeks. In our work we plan for longer periods but for most people planning a year ahead for everyday life is considered long term. Planning a career, a business, or a home requires more detailed and longer term planning but would not normally extend beyond the individual’s life time.
Thus it is inherently difficult for humans to relate to the incredibly long time frames within which the Universe and our planet have evolved. We of the Homo Sapiens species evolved to our present state during our hunter-gatherer phase. As hunter-gatherers we were oblivious to the Universe (other than the sun, moon and stars above) and to the invisible microscopic world that exists beyond the ranges of our human senses of sight, hearing, smell, and touch. Even the invisible air we imagined was some magical force or energy.
Once humans evolved speech we were able to invent explanations for the world around us. We composed poems and songs to remember important things and to pass on to our descendants.
Anthropocene
The time scale of recorded human civilization is a few thousand years. But this is a very short period compared with the Anthropocene period of about 200,000 years of Homo Sapiens’ existence on Earth. But the Anthropocene itself is only a tiny fraction of the 4.54 billion year age of the Earth.
Deep Time
Hence the attraction of the term Deep Time for scientists and others who study and communicate recent science discoveries involving geologic time scales of millions and billions of years into the past.
This concept of Deep Time features in the Introduction of a recent book by Dr Elsa Panciroli, “The Earth, a Biography of Life“. In her book, Panciroli recounts the history of life on Earth. She begins by explaining how the evolution of life traversed several geologic periods, each spanning millions of years within the timeline of life on our planet earth. Each period included changes to the Earth’s environment within which life was evolving. These changes, spanning millions of years, included geologic, ocean, continental, and climate.
The reader cannot help but be impressed by the diversity and complexity of the life on Earth as it evolved with new species appearing, existing for varying periods of time, and then going extinct.
Precambrian
Hadean
The first period of the Precambrian era, and of the Timeline of Life on Earth is the Hadean. This period began 4,600 million years ago and included the formation of the Earth. formed, The Earth was formed from out of the Sun’s accretion disk, along with the rest of the planets of the solar system. It was during this first eon of Earth’s existence that the Moon was created as the result of a collision of another planetary body with the Earth, sometimes called the Theia impact.
Archean
The second period on the timeline is the Archean. This period began 4,000 million years ago and witnessed the formation of the Earth’s crust, the beginning of Plate-tectonics, and the beginning of life in the sea.
The Late Heavy Bombardment is hypothesized to overlap with the beginning of the Archean. The Huronian glaciation occurred at the end of the eon. The Earth’s atmosphere during this period was very different in composition from today’s. The prebiotic atmosphere was a reducing atmosphere rich in methane and lacking free oxygen.
Proterozoic
The third period on the Timeline is the Proterozoic. This period began 2,400 million years ago and contained the Great Oxygenation Event. The Wikipedia article referred to here states: “Geological, isotopic and chemical evidence suggests that biologically produced molecular oxygen (dioxygen or O2) started to accumulate in the Archean prebiotic atmosphere due to microbial photosynthesis, and eventually changed it from a weakly reducing atmosphere practically devoid of oxygen into an oxidizing one containing abundant free oxygen”.
In simple terms, some of the first bacterial life on Earth were cyanobacteria that arose at the end of the preceding Archean epoch. The cyanobacteria evolved chlorophyll-based photosynthesis to convert CO2 into O2. This initially caused the Great Oxidation Event and the “rusting of the Earth” during the early Proteozoic. Then the build up of oxygen in the atmosphere and sea would have caused mass extinction of the earliest anaerobic life forms. However the oxygen enabled newer aerobic life forms to evolve that breathed oxygen. This in turn led to the evolution of eukaryotes during the Paleozoic.
Palaeozoic
Cambrian
The first period of the Palaeozoic era was the Cambrian period. This period began 541 million years ago. The Cambrian period saw the arrival of the first chordates, or animals with back bones. It also witnessed the “Cambrian explosion“.
The Cambrian explosion, or diversification, is an interval of time within the Cambrian in which there was a sudden radiation of complex life. If you are interested in the Cambrian explosion the Wikipedia article referenced here explains both the difficulties in studying this phenomena, due to the great age of the geology and the changing scientific opinion of the event. The fossil record that has been discovered to date, and in some cases reinterpreted, is subject to evolving scientific opinion of the nature and dating of the explosion in animal diversity both during and before this period. Some recent analysis argues that evolution of complex life began well before the Cambrian period.
While the appearance of these fossils is described as an ‘explosion’, the length of the Cambrian period is 56 million years. Also apparently, due the age of the geology, finding fossils in the Cambrian and Precambrian is quite difficult. Earlier geologic structures can be disrupted by later geology, seismic, and tectonic movement. There is evidence that the ‘explosion’ in the Cambrian does not necessarily indicate the beginning of the complex animal life and that complex animal life may in fact have originated earlier in the late Precambrian era.
Body Fossils
The body fossil in the illustration below, from Wikipedia’s ‘Cambrian explosion’ article referenced above, is of a Marrella specimen from the middle Cambrian Burgess Shale (British Columbia, Canada).
By Verisimilus at English Wikipedia, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2996075
Timeline of Life
All of the above is to illustrate the enormous time periods within which early life had evolved on Earth.
Terraforming
Terraforming an Earth-like, but otherwise originally lifeless, Exoplanet is not an obvious project. It is not just the challenges of preparing the planet’s climate, atmosphere, oceans and landforms to be suitable to harbour life but the equally incredible challenge to select and organise suitable simple and complex life forms to provide a habitable biosphere that is stable over an indeterminate period. As ecologists and biologist have observed when studying the Earth’s biosphere and its inhabitants, the complexity and diversity of life is not just a function of the complexity and diversity of and between individual species but the complexity and diversity of the interacting systems of life within which the individual life forms must live. Where do you start? With the single cell bacteria and other simple life forms? Do you follow that with more complex single cell life forms? When do you introduce plants, fungi, and then animals? Which species and in what combinations?
This is not a simple problem.
It is easy to imagine in one’s mind how the terraformed exoplanet might be arranged in its final idealized form at human macro-scale.
But what underlying unbelievably complex ecological foundation is going to be necessary, from nano scale chemistry, through biochemistry, and multitudinal life forms and biological systems, to achieve this idealized stable and safe habitable dream landscape?
This Deep Time post is the second in our new Life series of posts.
[Dated: 23rd December 2024].