The scientists decided to look at humanity's impact on the planet through a geological lens, in order to ask two simple questions: How big is it? How diverse is it? The answers provide some perspective of the scale of change people have of imposed upon the world especially within the last century, which is when they acquired the power to move such enormous amounts of material, Zalasiewicz said.
To arrive at their totals, they separated the technosphere into five different areas - urban, rural, subterranean, marine and aerial - and then estimated the area, thickness, density and mass for each based on existing data as well methods for collecting that data.
For example, although cities are planned, mapped and archived, the amount of materials and engineered substructures aren't systematically converted into geological terms or measurements that would be useful for this study. But archaeologists who look at the remains of ancient civilizations do have ways to measure and differentiate the urban layers from natural rock and mineral and their data is relevant to this study.
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Much more can be said about the aerial technosphere, where atmospheric gases and particulates are monitored and measured. Carbon dioxide created from human activity weighs almost one trillion tons.
Measuring the diversity of the objects also required some educated guessing. They adopted the method that palaeontologists use measure the diversity of fossil organisms and refer to objects created by modern humans as "technofossils."
One such example could be a book. Currently there are about 130 million book titles since publishing began, with a million new publications created each year in the United States. If viewed through a palaeontologist's lens, each title would be as a distinct entity, because it would have a specific dimension, texture, pattern of printed words and number of pages. The same could be said for mobile phones, of which the 6.8 billion individual phones manufactured might be classed into hundreds if not thousands of different 'technospecies'.
Considering these examples and others, the scientists guess that number of technofossils is in the billions.
"We've put in a very preliminary estimate," Zalasiewicz said. "What's clear is that the figure is very big, bigger than the number of living species on Earth."
Pinpointing the exact weight of the technosphere and amount of technofossils is a challenge. Zalasiewicz says that the numbers are a broad brush stroke and encourages others to try to find different ways for measuring both.
Ultimately they'd like to link the technosphere, its scale and diversity, with the processes involved in creating and maintaining it.
It's just a beginning. But one can't help wondering if it's a beginning of an end.