Abstract:
The long-term diversification of the biosphere responds to changes in the physical environment, whether geological or climatic. Yet, over the continents, the nearly monotonic expansion of life started later in the early Phanerozoic (540 million years ago) than in the marine realm, where instead the number of genera waxed and waned over time. A comprehensive evaluation of the changes of the geodynamic and climatic forcing misses to provide a unified theory for the long-term pattern of evolution of life on Earth. In this presentation, I will discuss recent work coupling climate and plate tectonics models to numerically reconstruct the evolution of the Earth’s physiography over the past 540 million years (Phanerozoic eon). These models are then compared to paleo-diversity datasets from marine animal and land plant genera. Our results suggest that biodiversity is strongly reliant on landscape dynamics, which at all times determine the carrying biodiversity capacity of both the continental and oceanic domains. In the oceans, diversity closely adjusted to the riverine sedimentary fluxes that provide nutrients for primary production. On land, plant expansion was hampered by poor edaphic conditions until widespread endorheic basins resurfaced continents with a sedimentary cover that facilitated the development of soil-dependent rooted flora, while the increasing variety of the physiography additionally promoted their development.
Bio:
Tristan’s research areas revolve around sediment transport, landscape evolution, coral reefs and ocean dynamics. He leads the EarthCoLab research group and his main activities consist in the design and implementation of open-source numerical codes that improve our understanding of the complex interactions between Earth’s surface, climate, tectonic, and its relationships to biodiversity. He moved to the University of Sydney in 2015 after working for 8 years at the Commonwealth Science & Industry Research Organisation (CSIRO). He did his degree in France in marine engineering and physical oceanography with a PhD in marine geoscience. Over the past 3 years, he has been designing holistic approaches enabling cross-disciplinary research by linking data to whole Earth models across temporal and spatial scales.
Summary:
Focus: landscape dynamics over geological timescales (hundreds of millions of years) over the global scale
Earth surface dynamics (living skin of the planet)
Tectonics: move crust up, deform it, create mountains
Surface processes: erosion due to gravity, weather
Earth’s surface appears very stable but are in fact transient: shaped by many forces and these changes affect us (e.g. landslides)
Earth’s landscape is a record of its history:
Earth’s climate and its regulation
Interactions between surface and biodiversity
How the course of life was driven by surface environments
Paleogeography
Inference from present-day tectonics
Reconstruction of past tectonic state
Sedimentary archives provide historical spapshots
Drives
Climate history
Natural resources
Origin and evolution of life
Goal: framework for quantifying our understanding of paleogeography and its reconstruction
Sources:
Paleo-climate
Erosion/deposition
Tectonics
Prediction: Geomorphic expression
Landscape evolution model
Change in elevation = Uplift + River-induced erosion/deposition + Hillslope processes
Global Scalable Paleo Landscape Evolution (gopl): https://github.com/Geodels/gospl
Implicit solver methods
Entire planet,
.5 x .5 degree ~ 5x5 km at equator
~1000 year time steps
Total simulated time 100-500million years
Inputs: Elevation (available at 5 million year increments), climate (2-3 degree resolution), tectonics (existing, independent reconstructions)
Outputs: landscape dynamics, reiver water& sediment flexes, sediment routing system, basin evolution
Model validation
Elevation:
Available data is spatially and temporally coarse
Model’s predictions are much finer
Can’t compare them directly because many details of model’s prediction will be somewhat differently placed in space/time and finer
Instead, create histogram of the distribution of different elevations in each region and compare histogram to available reconstruction data
Sediment accumulation:
Measure position of a river delta by looking at sediment deposits over time
Compare the delta location in model vs measurement
Water discharge & catchments dynamics: Earth’s circulatory system
Use sediment deposits to track evolution of rivers and their deltas
Question: How do river structure dynamics relate to evolution of biosphere?
Data shows that net sediment flux mirrors marine biodiversity (number of marine families) over past 500m years
Linear correlation = .88
Hypothesis: capacity for marine life to evolve depends on delivery of sediment
This implies that abiotic control (sediment) is as important as evolutional/biologic dynamics
Plants
Similar relationship between number of plant species and sediment delivery (correlation = .9)
Plants and sediments are linked and sediment may help plants but also plants may create more soil and sediment, so they likely drive each other
General trend: the increasing complexity of land surface shape also drives increase in species diversity