Rock's

It is possible to determine a rock's age thanks to radioactive elements.

"She, hurling Jove's winged lightning, stirred the deep / and strewed the ships. Him, from his riven breast / the flames outgasping, with a whirlwind's sweep / she caught and fixed upon a rock's sharp crest."

Triton, Cymothoe from the rock's sharp brow / push off the vessels. Neptune plies amain / his trident-lever, lays the sandbanks low, / on light wheels shaves the deep, and calms the billowy flow.

Ms. Trosper says Spirit's operators are extending its instrument arm to brush the Martian dust from Adirondack, get close-up images with its microscope camera, and determine the rock's mineral content with an infrared sensor. She notes that they will use an abrasion tool Tuesday to scratch below its surface before moving on to its next target.