Decoding Earth's History

Rónadh CoxGeosciences professor Rónadh Cox has spent her life deciphering rocks in faraway places— from gullies in Madagascar to reef sediments in the Caribbean and even as far away as Jupiter’s moon, Europa. Working with student co-authors, she recently made a breakthrough in understanding boulder movements atop the cliffs of Ireland’s Aran Islands. By painstakingly comparing current ridge lines with British ordnance survey maps of 1839, Cox and her students proved unequivocally that storm waves (not tsunamis, as some experts thought) are shifting rocks as heavy as 78 tons several tens of meters above high water, permanently changing the landscape. Though Cox’s research involves paying attention to even the tiniest of details, she explored some really big ideas—deep time, the origins of life and the stunningly young field of geology—with writer Ali Benjamin in February.

Earth is unbelievably old, while human history is extraordinarily new.

It’s nearly impossible to really comprehend the age of Earth— 4.6 billion years. Geologists often use metaphors to give a sense of scale. Imagine, for example, Earth’s entire history compressed into a single calendar year. If Earth formed at 12 a.m. on Jan. 1, our ancestors (the first Homo sapiens) wouldn’t appear until 11:40 p.m. on Dec. 31. The most recent 2,000 years of human history would take place in the final 14 seconds of the year.

Deep time can also be understood in a more visual way.

If you fit Earth’s history onto a standard roll of toilet paper with 1,000 sheets, each sheet would represent 4.6 million years. Nearly 90 percent of the roll (883 sheets) would be taken up by the Precambrian era—before complex and diverse life forms evolved. The dinosaurs would become extinct only about 14 squares from the end of the roll. Meanwhile, the entire 5,000 years of recorded human history would fit in just 1/1000th of the final sheet—less than the depth of the perforation line.

Early Earth was Hell…

During the earliest period on the planet, the Hadean era (so named because conditions were probably pretty Hellish), our solar system was still forming. Space debris routinely slammed into the Earth’s surface. There may have been “magma oceans,” which were large areas of molten rock. It was just a very violent period. By 3.8 billion years ago, the beginning of the Archean (“ancient”) era, things began to stabilize.

…maybe even a living Hell.

The oldest rocks that preserve their original features are 3.2 billion to 3.5 billion years old; in them we find microfossils, signals of tiny bacterial life forms. Rocks from the Hadean era aren’t well preserved, yet some researchers still believe that life could date to these early, violent years. Where did life come from? Possibly outer space; organic molecules are found in comets, and studies have shown that these molecules could withstand the impact of a comet hitting the Earth. Others think life could have formed at hydrothermal vents—mineral-rich underwater geysers so hot they can melt lead. Today, abundant life forms exist around these “black smokers,” with chemical energy from the vents, not sunlight, driving biological processes. The huge differences between these two ideas show how few answers we have to some of the most fundamental questions about life.

Geologists have learned a lot in a very short time.

Geology may study ancient forms and processes, but it is a stunningly young field; about 90 percent of geologists who ever lived are alive today. It wasn’t until the mid-19th century that people began to understand that Earth was more than a few thousand years old. When scientists began to propose that Earth’s age was in the tens of millions, still a vast underestimation, the public was shocked; most had never considered numbers that large. The idea of plate tectonics—continents shifting—began to be accepted only in the late 1960s, and deep-sea hydrothermal vents weren’t discovered until 1977.

And Earth is shifting before our eyes.

Geoscientists are accustomed to measuring change in millions of years, but an explosion of data and images in recent decades have revealed how fragile and interconnected our Earth systems really are—and how quickly they can change. Climate change is a perfect example of this. We don’t yet understand all the details—not of climate change, not of the origins of life, not of the moons of Jupiter and not even of the mysterious boulder movements on the Aran Islands. But each new field season and each student thesis provides another piece of the puzzle as we marvel at the beautiful complexity of our home planet.

Rónadh Cox is a professor of geosciences and chair of the maritime studies program at Williams. Since 1996 she’s taught courses as varied as “The Test-Tube Earth,” “Oceanography” and “Climates through Time” and has helped launch many budding geologists’ careers, leading scores of Williams students in research expeditions across the U.S. and around the globe. Ali Benjamin is a writer based in Williamstown.