Written in Dust
Many scientists fight a never-ending battle against dust in their laboratory. Gisela Winckler, however, can’t get enough. Before you send her what’s under your bed, though, she’s only interested in a very special kind of dust — the kind that rains down on the Earth from outer space. Winckler uses the tiny amounts of interplanetary dust she finds in sediment cores from the sea floor to get a clearer picture of the Earth’s geology and climate hundreds of thousands of years ago.
Currently a Doherty associate research scientist at the Lamont-Doherty Earth Observatory, Winckler began examining interplanetary dust as a post-doctoral researcher to, in her words, do something a little different. After studying physics as an undergraduate and isotopes of helium found in the ocean as a doctoral student, she turned to something so different that it could only come from space: extraterrestrial 3He, an isotope that is extremely rare on earth but highly enriched in interplanetary dust.
“I was really looking for an exit from classical physics,” said Winckler. “This was an opportunity to use basic physical principles to understand environmental systems.”
Every year nearly 40,000 tons of microscopic particles from asteroid collisions or passing comets rain down on the Earth. Much of this extraterrestrial debris is vaporized or melted in the atmosphere, its minute cargo of 3He lost. But a small amount of dust — mainly particles no bigger than the width of a human hair-- survives entry and settles to the bottom of oceans and lakes or is trapped in ice.
Scientists have known about interplanetary dust for more than a century. In the late 1800s, researchers on the HMS Challenger, the first vessel dedicated entirely to oceanographic study, discovered a small amount of something in clay samples raised from the sea floor that they could not match with any terrestrial source. They correctly surmised that it must have had a cosmic origin.
Today, scientists use high-altitude aircraft to gather samples of interplanetary dust and study the origin of the solar system. A NASA mission is also scheduled to bring dust from the tail of a comet back to Earth in 2006. But for paleoclimate experts like Winckler, it’s not the fresh dust that matters — it's the stuff that has been slowly building up in the climate archives of the Earth over centuries that tells a more important story.
Because interplanetary dust filters down through the atmosphere at such a constant rate, Winckler can use the trace amount of 3He in a piece of sediment core to determine how quickly the sediment itself built up. From this, she and others can determine such things as how quickly the Earth’s biologic systems recovered from the impact of the asteroid that killed off dinosaurs (about 10,000 years) or to study the periodic shifts in climate that ripple through the Earth’s past.
“The fact that you can even measure interplanetary dust never ceases to amaze me,” says Winckler. “That you can use this really rare extraterrestrial stuff to understand some basic processes on Earth is even more incredible.”