In this graph, we can see how human activities have influenced mercury in the atmosphere. The graph shows the results of a research project that studied a glacier core taken from Wyoming (Schuster et al. 2002). Scientists took a glacier core sample by drilling out a long tube of ice - from the Fremont Glacier Core, Wyoming (it was over 500 feet deep!) - and then slicing the core into layers of ice that each represent a period of time. The core sample showed the layers of snow that built up in Wyoming since approximately 1746. By measuring the amount of mercury in each layer of snow, scientists found that mercury levels changed over time. 

This graph shows the results of their work. On the vertical axis, we go back in time as we go down the core, to before the Industrial Revolution when mercury amounts were relatively low. We can see major volcano eruptions, like Tambora in 1815, but notice how quickly mercury comes back down to the baseline after the eruption. Since the Industrial Revolution took hold in the late 1800s and humans began burning more fossil fuels, mercury rates have increased (toward the right) and have never gotten back to that pre-industrial baseline. Unlike natural sources of mercury, like volcanoes, human influence on mercury emissions through industrialization is constant and never allows the system to recover.  Mercury, from natural or man-made sources, released into the air can move through the atmosphere for up to a year and travel far beyond its source before it settles into soil or water.