Thinking about the Earth as an object requires some imagination. As far as objects go, it is a really big one: The Earth’s diameter is about 8,000 miles (with a bit of variation when measured at the poles). It’s also very old—it has an age of about 4.5 billion years. It’s pretty dense too, and is composed of various chemical compounds, mostly silica, but also significantly alumina, lime, magnesia, water, carbon dioxide, iron oxide and so on.  

But there is something that textbook facts and measurements like these don’t really capture. It feels insufficient to think of the geological Earth as an object, when it is made of up so many connected and interdependent things, such as the atmosphere. It is an object of interfaces: the magma, the terra, the atmosphere, and so on—so many envelopes in which we live as part of deep space.

By the 18th century, increasingly accurate measurement techniques forced humans to consider the Earth as a scientific object. This shift required acknowledging the layered structure of the earth, and recognizing that this structure corresponds with temporality. Depth digs through time, and deep excavations down into the earth involved a kind of time travel…. MORE