On Earth Day this year, my friends and I stood on the Main Green for a few hours and asked passersby to guess the age of our planet. Our team of undergrad geology students had laid out a timeline of Earth’s history that spanned the Green: The formation of Earth was under Faunce Arch, the oxygenation of the atmosphere in front of Sayles Hall, the extinction of the dinosaurs in front of the John Carter Brown Library and the entire life of Homo sapiens squeezed into 0.7 centimeters only a meter away from the dinosaurs. We invited students to take a piece of sidewalk chalk, add an event to the timeline and revel in the wild and wonderful history we inherit as Earthlings.
Students’ guesses for the age of Earth were far-flung. “A couple million years?” “Must be older than me!” “Maybe a trillion years.” The most common answer? “I truly have no idea.” Six semesters ago, before I took my first geology class, I certainly would not have known that the Earth is 4.5 billion years old. American high schools seem to agree that Rome matters, the World Wars matter and sometimes, Mesopotamia and Vietnam matter, too. But the Earth? Why would it matter whether the Earth is four million or 4.5 billion years old? Our history educations stop at human timescales, leaving geology and Earth history to collect dust in old books.
After four years as a history and geology concentrator, I’m not only obsessed with both human and planetary timescales, but I think that we are irresponsible in studying either in isolation. (I once tried to count a geology class toward my history concentration, though I was unsuccessful.) Earth history puts human history in (measly) context; human history allows us to understand our relationship with Earth through different languages and lenses. At Brown, my professors in the geology department have taught me that the age of the Earth matters for the same reasons that my professors in the history department have taught me the Middle Ages and Industrial Revolution matter: because the past helps us render judgments on the present and imagine different futures.
If we use the past — and our relative distance from different pasts — to understand ourselves, then we need accurate timescales. The Industrial Revolution, for example, takes on a different meaning in the context of Earth history, which teaches us that carbon dioxide concentrations in the atmosphere have not reached the present 415 parts per million since around three million years ago, when sea levels were 60 feet higher than they are today. Deeper timescales also help us recognize the fact that the coal powering the Industrial Revolution formed over a 300-million-year journey in Earth’s crust before being burned in two centuries. Now that’s nonrenewable.
This work of reconstructing the past is not easy. Over the past four years, while rushing to lab in the Geo-Chem Building or history section in Peter Green House, I’ve been caught off guard by the command etched into the side of the John Carter Brown Library: “Speak to the past and it shall teach thee.” We’re not asked to learn from the past, but to speak to it. The verb is resoundingly active.
What pasts do we speak to? We’ve learned at Brown that some pasts are more accessible than others. But that doesn’t excuse us from ignoring the histories buried most deeply. I’ll long remember Associate Professor of History Naoko Shibusawa teaching us third-year history students to “read against the grain” for voices missing in the history archives. The geologic past, as a rule of stratigraphy, is generally buried deep. I confronted this reality on Geology Field Trip #1 in GEOL0220, when our professors, Jan and Karen, brought us to North Attleboro, Massachusetts, and asked us to read the rocks. (As you can imagine, the rocks of North Attleboro are not the rocks on the cover of our geology textbook). Initially, the rocks seemed illegible. But over the next two hours, Jan and Karen helped us decode each paragraph of the story: A layer of larger sand grains hinted at a river flood; parallel scratches across the surface suggested the scouring of a retreating ice sheet. As it turned out, there was an accessible past written into these rocks. We just needed to learn how to read it.
At Brown, we’ve made the commitment — radical to some but routine to us — to read the pasts that are hardest to access. Every day, I am reminded of the urgency of this commitment. How can we write our future if we can’t read our past? How can we imagine future climate change if our conception of the possible doesn’t include the world three million years ago, when trees grew in Antarctica and the eastern seaboard of the U.S. was flooded and carbon dioxide concentrations last matched the levels we’re causing now? As you go about reading deep histories, Class of 2019, I’m sure you’ll run into sandstones that seem illegible and siltstones that stare blankly back. But I’m confident that you’ll find a way in. I’m confident that you’ll read to understand, to challenge and then to transform. Get out there, read history and rock the world.