What is deep time and is it important?
The Deep-Time Digital Earth (DDE) program of the International Union of Geological Sciences is one of the first mass attempts to bring together large amounts of geological data on the Earth’s geological history – meaning its history well before the advent of mankind and even before the appearance of life on planet earth. But for many people - non-scientists particularly – ‘deep time’ would appear to have little relevance. It may make people wonder at the huge expanses of time that stretch well past our personal and human histories into the dim past, but is deep time really important?
In this blog I argue that deep time is important, not just because it can tell us quite a bit about earlier states of the earth for example earlier climatic states and biodiversity, but also because it frames the resources of the Earth which we all rely on, whether geothermal heat, groundwater or minerals.
But what is deep time and when did it start? Deep time was a phrase introduced by the writer and journalist John McPhee in his book Basin and Range (1981), so in a sense it was a journalistic invention that offered a metaphor for the obscurity and unidirectional nature of geological time. Although McPhee didn’t define the start of deep time, many geologists draw the line of the start of deep time at the start of the Quaternary around 2.5 million years ago. So one definition of deep time might be ‘pre-Quaternary time’ - all the ages of the earth from its formation around 4.5 billion years ago to 2.5 million years ago. This is well over 99% of the totality of Earth’s history. Other geologists who see deep time as anything before the advent of the industrial age (the ‘Anthropocene’) would count an even greater percentage of Earth’s history as deep time.
Are there are any practical reasons to study the events of deep time? Many geological palaeoclimatologists and palaeontologists – those working on Earth events, for example from the Cretaceous, Palaeocene, or Pliocene - claim that their work has a direct bearing on our understanding of modern climate change and biodiversity. In their words, looking back into deep time helps us to understand our modern climate change and biodiversity problems.
Indeed deep time geological research does help us see the effects on the grand scale of geochemical cycles (such as the geological carbon cycle ) on past environments with implications for our own environment. It shows that natural processes such as large scale volcanism or methane release from seabed or soil hydrates are perfectly capable of altering the environment very radically. Different effects are also able to combine forces into positive feedbacks that propel environmental change into top gear or ‘runaway’ climate change.
Of many possible examples of big earth events, the Permian-Triassic extinction and the Palaeocene-Eocene Thermal Maximum (PETM; Fig. 1) are good examples of what changes we might expect in our own future because they are associated with increased greenhouse gases in the atmosphere and global warming. Geologists and stratigraphers can show that there was warming, changes in the hydrological cycle, sea level and salinity, animal and plant life, and of course extinction. These help us see what might be ahead.
Fig. 1. The temperature spike (in the green line) of the PETM from δ18O of fossil shells. (From Wikipedia, This figure was prepared by Robert A. Rohde from published and publicly available data and is incorporated into the Global Warming Art project)
Amongst the direct contributions of DDE scientists has been study of biodiversity through time. A major DDE objective is to employ fossil data to unravel details of life’s unfolding story. The fossil record suggests that Earth has experienced a long-term gradual diversification of life as suggested by phylogenies based on living organisms, and data from fossils from the last 600 million years. Precise biodiversity is hard to determine from the deep-time fossil record because only a small fraction of organisms living at any given time are thought to have been preserved as fossils, but new models (Fig. 2) can take into account preservation and sampling biases using artificial intelligence.
Fig. 2. Fan et al. (2020) employed paleontological big data and artificial intelligence algorithms to reveal marine biodiversity for 10 major fossil groups. This analysis demonstrates both dramatic mass extinction events and rapid recovery of biodiversity.
But is there practical knowledge or advice that a deep time climate change scientist can pass on to the people that really need to plan for modern climate change or biodiversity loss – for example policy-makers, regulators and governments? These planners may be faced with decisions on how to spend Government budgets on sea defences, health care for new diseases, agricultural practices, and ecosystem services such as pollination.
There are a few problems with a deep time climate change and biodiversity scientist being able to provide practical guidance. The first is the huge difference between the periods of time that these two types of specialists deal in. Policy-makers and regulators look ahead weeks, months and, if they have sufficient budget, years. Deep time palaeoclimatologists deal in hundreds of thousands, and (mostly) millions of years. Could a palaeoclimatologist looking at the rock cores from the PETM provide measures of sea level rise that a coastal planner wondering about building future local coastal defences would be able to use? Could a PETM specialist advise an agriculture policy maker or a public health specialist? Could an expert on the biodiversity of the Permian-Triassic extinction provide data to help with maintaining modern ecosystem services? This is seems unlikely at the moment. The precision needed is far beyond what deep time can provide.
Deep time palaeoclimatologists and palaeontologists also find it hard to interface with planners and policy makers because of the differences between the worlds that they are dealing with. The PETM world was very different to today: for example there was no Atlantic Ocean, the North Sea was enclosed to the south where the English Channel now divides England and France, and the PETM began at a time of already elevated temperature.
Planners and policy makers get information about climate and biodiversity change through climate projections or scenarios which are derived from complex models that essentially extend weather forecasting - rather than anything directly derived from deep time data. In the United Kingdom for example the UK Climate Projections (2023) can be used. These projections provide information about the implications of climate science and attempt to quantify the uncertainties of predictions. In general the UK Climate Projections suggest warmer and wetter winters, hotter and drier summers, sea level rise, and more severe weather for the UK. This kind of information is the most useful for policy makers and planners. Deep time climate research can’t - at least at the moment - help planners or policy makers make decisions.
However the most refined and sophisticated paleoclimatic studies and modelling, for example the Pliocene Research, Interpretation and Synoptic Mapping (PRISM 2023) projects of the United States Geological Survey (USGS) can help to refine and future proof climate projections. PRISM uses palaeoclimate reconstruction and Pliocene sea-surface temperature models to independently test modern climate models and judge the likelihood of tipping points using an appreciation of boundary conditions that might be unaccounted for in modern modelling. Thus palaeoclimate data are probably best suited to test models at the edge of their ability and there is no other source of this capability but deep time.
Another place where deep time is really important is in communicating the reality to ordinary people that the earth does not stay the same, but has been subject to climate and other changes in the past. Deep time climatology, extinctions and earth events, compel the public to engage with the science of climate change, and to listen seriously and critically to the analyses of the risks associated with climate change. Although this sounds rather intangible it is hard to imagine a more dramatic example of abrupt environmental change than the end-Cretaceous extinction of the non-avian dinosaurs. This is an event that most people know something about. The event has been covered in the media endlessly and has found its way into literature and the arts as a symbol of the fragility of the earth system. An appreciation of the event helps people to see that Earth’s balance is something that can be upset - and by extension that humanity can upset that balance through, for example industrialisation.
So deep time in a way not only reveals the fragility of the earth but also provides information on the ‘wild cards’ that we don’t include in our modern climate forecasting.
I think the final point to make is where deep time is very much undervalued. The earth is a product of its history. This seems an obvious thing to say, but it’s important because of the way that human beings interact with the Earth and benefit from its resources. The arrangements of tectonic plates in deep time, and the paleogeography of the continents as they have evolved through time, have had an enormous influence on the distribution of minerals and of hydrocarbons for example. They have also influenced evolution, for example the evolution of our own species Homo sapiens. Because we know the configuration of the continents and a lot about plate tectonics we know where to look for certain resources. By looking at the deep time arrangement of plates (for example) there is a lot we can reveal about the world, and a lot we can use to predict the distribution of useful resources.
Let’s take copper for example. Copper is going to be very important in the energy transition as we develop more electric vehicles and batteries for energy storage. Porphyry copper deposits (PCDs) are one of the main sources of copper. They are concentrated in western South and North America and Southeast Asia and Oceania - along the Pacific ‘Ring of Fire’. PCDs are generated in continental arcs in response to plate convergence, subduction and collision. To investigate the clusters of PCDs and their governing factors requires analysis, including frequency distribution and size distribution, temporal distribution (i.e., number and sizes of deposits versus age), and spatial distribution along a profile parallel or perpendicular to the subduction zone. In order to understand the governing factors of clustering, the PDC clusters can be compared with abrupt changes of the kinematical properties of plate motions, as well as geometrical properties of subducting slabs (Fig. 3). DDE has pioneered the integration of various geodatabases through deep time to link processes associated with subduction with mineralization processes in the crust. DDE data and interpretation will allow for a better understanding of the processes leading to formation (distribution, size) of PCDs, which are vital for modern industry, technology, and decarbonization. Linked databases and models can be used to gain insights into porphyry copper deposits that are not possible through simple analysis of single or pairs of databases. DDE will link georeferenced databases and models of this type so that they can be used more efficiently.
Fig. 3. Clusters of PCDs vs local change of subduction slab geometry in the Andes (Cheng, 2019)
In a similar way, the evolution through deep time of sedimentary basins and the linking of diverse databases will allow models to be built of the evolution of permeability (for example for groundwater) and deposition of rock salt (for the storage of gases like hydrogen for a hydrogen economy). So deep time study will enable DDE and scientists working with DDE data and platforms to understand the resources that we need for society.
In conclusion, deep time is important – not only because it illustrates the fragility and interconnectedness of the Earth system and feeds into understanding climate change - but also because the distribution of many geological resources for the well-being of society are broadly governed by processes that began in deep time.
References
Cheng, Q., 2019. Integration of Deep‐time Digital Data for Mapping Clusters of Porphyry Copper Mineral Deposits. Acta Geologica Sinica‐English Edition 93, 8–10.
Fan, J., Shen, S., Erwin, D.H., Sadler, P.M., MacLeod, N., Cheng, Q., Hou, X., Yang, J., Wang, X., Wang, Y., Zhang, H., Chen, X., Li, G., Zhang, Y., Shi, Y., Yuan, D., Chen, Q., Zhang, L., Li, C., Zhao, Y., 2020. A high-resolution summary of Cambrian to Early Triassic marine invertebrate biodiversity. Science 367, 272–277.
McPhee, J. 1981. Basin and Range. Annals of the Former World. ISBN 0-374-10520-0.
PRISM retrieved 2023 https://www.usgs.gov/centers/florence-bascom-geoscience-center/science/pliocene-research-interpretation-and-synoptic
UK Climate Projections (UKCP) retrieved 2023 https://www.metoffice.gov.uk/research/approach/collaboration/ukcp/summaries/index