Macrostrat exists to make the rock record quantitative: to describe how much rock of each kind, age and character is present in the Earth's crust, where it is, and how that changed through time.
Macrostratigraphy
Geologists have described the lithology, fossils and chemistry of crustal rocks since the nineteenth century. Most of that knowledge is recorded as local observations (stratigraphic columns, maps, measured sections, samples), each of which provides strong evidence about one place at one time. What these records do not easily provide is the aggregate picture: the total extent of marine sediment in the Cambrian, or the share of the crust made of igneous rock at a given age.
Macrostratigraphy is the approach of compiling rock records comprehensively enough to answer such questions. Its roots go back to the global tabulations of rock volume and composition made by Alexander Ronov and colleagues between the 1950s and the 1980s. Macrostrat has developed alongside the modern form of the approach, and macrostratigraphic analyses drive most of its scientific results.
Tabulations of rock quantity have opened new lines of research, including:
- the coevolution of life and the environment, and the influence of the preserved rock record on apparent patterns of biodiversity and extinction;
- the structure and origin of the Great Unconformity;
- the contribution of igneous rocks to the crust through deep time;
- the burial of organic carbon and the history of stromatolites, by combining rock abundance with proxy records.
Rock abundance also gives a baseline for interpreting sample-based records. A gap in fossil or geochemical data may mean that something did not happen, or simply that suitable rocks are not preserved; knowing how much rock of the right kind exists is what tells these apart.
A scaffold for other data
Because Macrostrat describes rocks explicitly in space and time, it provides a scaffold to which other geologic datasets can be attached: fossil occurrences, geochemical measurements, ocean-drilling cores, and descriptions drawn from the literature (see Linking data). Linked to that scaffold, each record gains context it does not carry by itself, such as a better-constrained age, a lithology, or its place in a regional succession.
A community index of physical geology
A record of the basic physical properties of rocks is useful well beyond global analyses. Compilations of mapping and stratigraphic data are slow to assemble, and aggregating them on a common platform makes them easier to find and use. Through its public Data services, Macrostrat provides geologic context to education, field work, museums, exploration and many software applications, most prominently the Rockd mobile app.
Toward a digital crust
A long-standing goal in geoinformatics is a "digital crust": a multiscale, multimodal model of the Earth's crust structured for modern computational work, which could transform geologic research in the way that global circulation models transformed atmospheric science. Experience suggests that such a model will not be built from the top down. It has to emerge from the bottom up, through collaboration across geoscience subfields, human-centered software, open data sharing and new ways of encoding geologic insight.
Macrostrat aims to be one of the connective frameworks such a model needs: a shared, linked representation of the crust that a broad community can build on and improve. Version 2 of Macrostrat is a step in that direction (see Version 2).
Further reading
- Peters, S. E., Husson, J. M., and Czaplewski, J. (2018). Macrostrat: A platform for geological data integration and deep-time Earth crust research. Geochemistry, Geophysics, Geosystems, 19, 1393–1409. doi:10.1029/2018GC007467
