Welcome to Core Elements' 100th issue. Over the past 100 weeks, we have covered hundreds of new studies and research findings on geoscience topics ranging from basins, mountains, rocks, and minerals to oil, gas, hydrogen, geothermal, and other reservoirs.
For this benchmark edition, I have selected something different: humans as a geological force. The concept is not new; it was discussed even in my student years. However, anthropogenic sediments and sand mining have attracted much attention in recent years. Let’s review these developments.
Rasoul Sorkhabi
Editor, Core Elements
Anthropogenic Sediments
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Anthropogenic sediments, or human-made materials, such as metals, glasses, plastics, textiles, and artificial objects, have increasingly accumulated in various environments, especially since the 1950s or the beginning of the Anthropocene—the Age of Great Acceleration.
New study: In The Sedimentary Record, Catherine Russell suggests a classification scheme for “anthropogenic sedimentary facies.”
This classification considers sedimentological principles and incorporates:
Bed-scale features such as layering, consolidation, cementation, and density
Grain-scale features such as porosity, clast-matrix ratio, sorting, and orientation
Sedimentary structure descriptions
Composition of sedimentary matrix (sandy, etc.) and anthropogenic material (plastic, glass, metal, textile, etc.)
Two groups: The author classifies anthropogenic sediments into two major groups:
Group 1. Bound: Materials bound to a layer in various ways. These are contained within the layer (like a clast, so that it cannot interact with the outer environment) or combined with, and attached to, the layer.
Group 2. Unbound: Materials forming bedded structures with various forms, grain sizes, densities, and directions.
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From 1950 to 2017, about 9,200 million tons of plastic were manufactured. Of this, about 5,300 million tons were discarded.
Plastic waste is now found in nearly every terrestrial and marine environment.
New study: In Earth-Science Reviews, Catherine Russell and colleagues have presented a sedimentological methodology for characterizing the properties of plastic waste.
Plastic classification based on size:
Giga-plastics: Larger than 10 meters
Mega-plastics: 1–10 meters
Macro-plastics: 5 centimeters–1 meter
Meso-plastics: 5 millimeters–5 centimeters
Micro-plastics: 1–5 millimeters
Nano-plastics: Less than 1 micrometer
Plastic classification based on density (grams per cubic centimeter):
Density: 0.83–0.92
Chemical type: Polypropylene (PP)
Examples: Bottle caps, rope
Density: 0.89–0.98
Chemical type: Polyethylene (PE)
Examples: Plastic bags
Density: 1.04–1.10
Chemical type: Polystyrene (FPS)
Examples: Floats, containers
Density: 1.02–1.16
Chemical type: Polyamide (Nylon)
Examples: Fishing nets, clothing
Density: 1.10–1.58
Chemical type: Polyvinyl chloride (PVC)
Examples: Plastic film, household plumbing
Density: 0.96–1.45
Chemical type: Polyethylene terephthalate (PET)
Examples: Plastic bottles, carpet, clothing
Density: 1.19–1.31
Chemical type: Polyvinyl acetate (PVA)
Examples: Adhesives, paints
Plastic classification based on shape:
Texture or surface roughness (from very rough and uneven to highly smooth)
Roundness (very angular to highly rounded)
Sedimentology of Plastics Conference
In 2024, the Royal Society organized a meeting on the sedimentology of plastics at Aston University in the United Kingdom. Eleven papers from this meeting are published in a special issue of the Philosophical Transactions of the Royal Society.
In an introductory paper within this special issue, Hampson and colleagues highlight four major research frontiers:
Physical properties and transport: The density, shape, and surface textures of plastic particles govern their transport, fragmentation, and abrasion.
Chemical properties and degradation: Surface chemistry and weathering characteristics of plastic particles determine their transport, fragmentation, degradation, and propensity to form mixtures and aggregates.
Monitoring the distribution of plastic sediment grains: Sampling and monitoring plastic sediments in various sedimentary environments (e.g., rivers, floodplains, estuaries, and beaches)
Source-to-sink plastic sediment budgets: Geochemical fingerprinting of plastics to constrain the transport pathways between these environments and establish volumes and fluxes of plastic that move between, or are held within, environments
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Popular Mechanics has a feature article on sand thieves and the importance of sand as a building block of the modern world.
According to one UNEP geologist, “We are extracting more sand material than is being replenished.”
Some facts about sand:
Next to water, sand is the second most-used resource in the world. It is used extensively within the concrete, glass, microchip, and shale fracturing industries.
Construction accounts for 85 percent of the total sand mined.
Currently, 40–50 billion tons of sand are mined annually.
Of this, only 38 percent is mined legally.
Beaches vs. deserts:
The world’s beaches are estimated to contain 7.5 quintillion sand grains. That is 7.5 with 18 zeros!
Beach sand is coated with salt and needs to be washed before industrial use.
Deserts also contain huge amounts of sand. The Sahara Desert is estimated to have 1.5 septillion grains of sand (1.5 with 24 zeros).
Desert sand is too smooth and rounded for commercial use. Beach and riverbed sands are preferable because their sand grains have a rough texture and bond better with cement.
Exploring solutions: Several solutions, some developed and others in development, have been suggested:
More regulations to fight illegal sand mining
SandID: Zachary Sickmann of The University of Texas at Dallas is training AI to create a data platform for tracking the provenance of sand grains.
Recycling: The European Union requires industries to recycle 70 percent of sand from construction and demolition waste.
Fly ash: Construction firms in the Netherlands collect fly ash from coal burning and process it as sand grains for concrete and cement.
Recycled plastic waste: Crushed plastic can be processed and added to sand aggregate. Research published in Hybrid Advances shows that a blend of 40 percent plastic and 60 percent sand provides a strong material.
Go deeper: Read this article I wrote for AAPG’s Explorer to learn more about sand mining and its effects.
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