To find out how fast, and how much, polar ice might melt in the future, scientists are looking to ancient rocks for clues of what happened in the past.
The day of our departure didn’t begin well for Paul Hearty. A clasp had ripped off his favorite clogs. A screw in his glasses had fallen out. His hasty repair, a safety pin in a hinge of his shades, gave him an incongruous punk look. The expedition—a drive from Melbourne across Australia’s southern and western coasts, in search of rocks—had also suffered a series of small setbacks and delays, provoking Hearty’s impatience and ire.
When he’s agitated, Hearty’s brows bunch into furrows reminiscent of the crevasses of glaciers he once studied. His eyes are light bluish-gray and deep set. He wears Crocs and no socks in dry weather, and ankle-high leather boots with white socks in the rain. Around his neck he wears a nylon cord, soft from wear, with two small hand lenses. The larger lens, a 10x magnifier, has a case engraved with his initials, PJH.
For thirty years, Hearty has labored to prove that if Earth warms just a couple degrees, as many scientists forecast, the huge glaciers in Greenland and Antarctica could melt substantially in mere decades. He bases his predictions on his studies of two recent (geologically speaking) warm spells 125,000 and 400,000 years ago. Hearty believes that Earth’s sea level rose 20 meters, about 65 feet, during the earlier of these heat bouts—higher than almost anyone else has yet determined. If Hearty is right, global warming poses a greater threat to the world’s coastlines than anyone is prepared for.
Hearty had been invited to Australia to scout for marine fossils once domiciled on a shore but left high and dry millions of years ago when the sea receded. The invitation itself was something of a surprise. It had come from Maureen Raymo, a geochemist who had earned her scientific kudos analyzing gummy seafloor sediment. She’d rarely handled limestone and sandstone—hard rocks—like those she wanted to collect in Australia. She’d once owned a rock hammer, but had long since lost it.
Hearty, on the other hand, had blistered his palms for decades cracking open such rocks. He reads them. Miles from any current shoreline, he might see scrub-covered limestone and fossilized coral, but his mind’s eye sees surf and spray and dunes. In the field, Hearty stares at rocks, sometimes from several angles. He tastes them with the tip of his tongue. He strikes them with his hammer and listens to the pings.
Hearty and Raymo, then, were not likely colleagues. Hearty generally disdains geochemists, and Raymo harbored questions about Hearty’s 65-foot finding. They’d joined forces because he wanted the grant-funded work, and she needed his skills. Together they formed a team that promised to accomplish what had proved elusive to many other scientists: to determine the level of the sea about 3 million years ago, the period geologists call the Pliocene.
Hearty had studied warm periods more recent than the Pliocene, thinking they could be analogs to our near future. But while he studied, the cars and homes and factories of modern civilization filled the air with even more planet-warming carbon dioxide. The air now contains as much carbon dioxide as during the Pliocene, when the planet was warmer than at any time since.
Raymo’s reservations about the accuracy of Hearty’s 65-foot sea level calculation did not change her high regard for the man. She still admired his clairvoyant ability to envision that moment in the past when a million-year-old rock was formed. Raymo affectionately calls him the Rock Whisperer.
Can ancient rocks really tell us how fast and how much polar ice will melt? Hearty believes they can, unequivocally. Such predictions matter tremendously. The world’s glaciers and ice sheets hold about two percent of Earth’s water. It’s a small fraction, but if all of it—about 6 million cubic miles of water—melted and poured into the oceans, the sea would rise by more than 230 feet. Most of today’s largest cities would vanish. A map of this waterlogged world would be missing Florida, the eastern shore of Maryland, Bangladesh, and Denmark.