“Now, now. Of course Mr. Jones here is absolutely right.”

Jones looked startled.

“It doesn’t matter how much you know about the San Gabriel Mountains. Of course not. It doesn’t really matter what you know about the Moon. What does matter to me, though, is that for you to make your mission into a full-up success, you’re going to have to learn how to observe.”

A full-up success. Ben Priest was suppressing a grin; York wondered if he had coached Romero to throw dumb-fighter-jock slang at Jones.

It caught Jones off-balance, anyhow. He bent and picked up a piece of the white rock. “Just tell me what the hell the relevance of this is.”

“It is called anorthosite,” Romero said evenly. “And it is our best guess that this was the primary component of the Moon’s primordial crust.”

“Really?” Adam Bleeker stepped forward and took the piece of rock from Jones — as if it was the only sample of anorthosite in the valley, York reflected wryly. “How so?”

Jones still glowered, but he was sidelined from the conversation, and Romero was back in control.

“When it first formed, the Moon was probably entirely molten. Then the outer hundred miles or so cooled to form a crust of anorthositic rocks — bright rocks, just like these. The main components of anorthosites, you see, like plagioclase, are light; heavier minerals, including those rich in iron and magnesium, sank into the body of the Moon. Now, the anorthosite — we think — dominates the brighter, older areas we see on the Moon’s face, while the dark maria are cooled seas of lava.”

Bleeker was grinning at the idea. “So the maria really were seas, once.”

York nodded. “It must have been a hell of a sight, back then: oceans the size of the Mediterranean brimming with red-hot, molten lava…”

She tailed off. Jones, his eyes hidden by his sunglasses, was watching her as she spoke, and cracking some joke to Ben Priest. Something crass, about the way she moved her eyebrows up and down when she was talking.

Ben looked uncomfortable, caught between a grin with his crew commander and embarrassment for his friend.

And York was silenced, just like that. She felt as if she was sixteen again, gawky, clumsy, infuriated.

With a fling of the arms, a grand actor’s gesture, Jorge Romero walked a few yards away. “Listen to me. I want you to leave this place as better observers, after today. But I also want you to leave with something else: a sense of the great drama of geology.” He glanced around. “When you look at a valley like this, you see a few dusty old rocks, perhaps. But I see immense processes which churn the surfaces of worlds, frozen in time as if by a flashbulb. I am sure Natalie has the same perception. It is only our mayfly life spans which restrict us all from seeing this.