Innermost, extending from the center about a fifth of the way outward, was a brown zone labeled SOLID INNER CORE — CRYSTALLINE IRON + NICKEL … 0-1227 KILOMETERS.
Next came a reddish shell, about twice as thick. LIQUID OUTER CORE — IRON + OXYGEN + SULFUR … 1227-3486 KILOMETERS, the caption read.
The beige stratum beyond that took up nearly the rest of the planet. MANTLE, the legend stated. OXIDES OF SILICON, ALUMINUM, AND MAGNESIUM (ECLOGITES AND PERIDOTITES IN PEROVSKITE FORM) … 3486-6350 KILOMETERS.
All three great zones featured subdivisions marked by dashed lines, tentative and vague lower down, with captions terminating in question marks. At the outermost fringe Teresa discerned a set of thin tiers labeled: ASTHENOSPHERE, LITHOSPHERE, OCEANIC CRUST, CONTINENTAL CRUST, HYDROSPHERE (OCEAN), ATMOSPHERE, MAGNETOSPHERE. Outlining that final zone, curving arrows rose from near the south pole, to reenter in Earth’s far northern regions.
The speaker at the front of the room was a trim blonde woman who pointed to those arching field lines.
“We were especially interested in the intense high-energy region astronauts call the ‘South Atlantic devil,’ a magnetic dip that drifts westward about a third of a degree per year. These days it hovers over the Andes…”
Using a laser pointer, she traced the high, diffuse fields that were her specialty. The woman obviously knew a thing or two about space-borne instrumentation.
She ought to, Teresa thought.
As a consultant transferred to Houston two years ago, June Morgan had become friends with several members of the astronaut corps, including Teresa and her husband. In fact, Teresa had been glad, at first, when June was assigned to work with Jason on a recent Project Earthwatch survey. Now, of course, Teresa knew her husband had been using that assignment to cover other work for Colonel Spivey.
That hadn’t kept him from getting to know June better, though. A whole lot better.
When Manella had brought Teresa in to introduce to everybody, June barely met her eyes. Officially, there was no grudge between them. But they both knew things had gone farther than any modern marriage contract could excuse. The one Teresa had signed with Jason made allowances for long separations and the planetbound spouse’s inevitable need for company. Their arrangement was no “open marriage” stupidity, of course. It set strict limits on the duration and style of any outside liaison and specified a long list of precautions to be taken.
The agreement had sounded fine four years ago. In theory. But dammit, Jason’s affair with this woman had violated the spirit, if not the letter, of their pact!
Perhaps it had been Teresa’s fault for following her curiosity, for checking who Jason had seen while she was away on a long-duration test flight. She had been shocked to learn that it was a NASA person… a scientist no less! A groupie, even a bimbo, would have been okay. No threat there. But an intelligent woman? A woman so very much like herself?
She recalled the feeling of menace that had flooded her then, creating a horrible tightness in her chest and a blindness in her eyes. For hours she had walked familiar neighborhoods completely lost, in a cold panic because she had absolutely no idea where she was or in what direction she was heading.
“You want me to give her up?” Jason had asked when she finally confronted him. “Well, of course I’ll give her up, if you want me to.”
His infuriating shrug had driven her crazy. He’d managed to make it sound as if she were the one being irrational, choosing this particular case to get jealous about all of a sudden. Perhaps illogically, she didn’t find his blithe willingness to go along with her wishes calming, for underneath his acquiescence she fantasized a regret she could not verify in any way.
His sojourns aloft were generally longer than hers. She had spent many more long days alone on Earth between missions, surrounded all the time by overtures. She’d seldom availed herself of those dubious comforts, whatever the freedoms allowed by their contract. That he’d been less reticent when he was home alone hadn’t bothered her till then. Men were, after all, inherently weasels.
She’d tried to remain civilized about it, but in the end Teresa let him go to space that last time with barely an acknowledgment of his farewell. For weeks their telemetered messages were terse and formal.
Then came that fatal day. As she was docking her shuttle, unloading her cargo and preparing to send Spivey’s peepers across the transitway, Teresa had been emotionally girding herself to make peace with Jason. To begin anew.
If only—
Teresa pushed away memory. It probably wouldn’t have worked out. What marriage lasted these days, anyway? All men are pigs. She missed him terribly.
One glance told Teresa she wasn’t alone in mourning. Meeting June Morgan’s eyes in that brief moment, she knew the other woman’s pain was akin to her own. Damn him. He wasn’t ever supposed to fling with anyone he liked. Especially someone like me! Someone who might compete for his love.
That instant’s communication seemed to cause the blonde scientist to stumble briefly in her address. But she quickly recovered.
“… so for… for most of the twentieth century, Earth’s total magnetic field weakened at an… average rate of four hundredths of a percent per year. And the decline has steepened recently. That, combined with a greater than expected drop in the Earth’s ozone layer, leads to a growing suspicion we may be about to experience a rare event — a complete geomagnetic reversal.”
The man across from Teresa raised his hand. “I’m sorry, Dr. Morgan. I’m just a poor mineralogist. Could you explain what you mean by that?”
June caused the display to zoom in upon a long, jagged, S-shaped range of undersea mountains, threading the middle of the sinuous Atlantic Ocean. “This is one of the great oceanic spreading centers, where older crust is pushed aside to make room for new basalt welling up from the mantle. As each fresh intrusion cools and hardens, the rock embeds a frozen record of Earth’s magnetism at the time. By studying samples along these ridges, we find the field has a habit of suddenly flipping its state… from northward to southward, or vice versa. The change can be quite rapid. Then, after a long period of stability, it flips back the other way again.
“Way back during the Cretaceous, one stable period lasted almost forty million years. But in recent times these flip-flops have taken to occurring much more rapidly — every three hundred thousand years or so.” June put up a slide showing a history of peaks and valleys crowding ever closer together, ending with a slightly wider patch near the right-hand edge. “Our latest stable interval has exceeded the recent average.”
“In other words,” Pedro Manella suggested, “we’re overdue for another flip.”
She nodded. “We still lack a good explanation of how geomagnetism is generated, down where the core meets the mantle. Some even think sea level has something to do with it, though according to the Parker model…” June stopped and smiled. “The short answer? Yes, we do seem overdue.”
“What might be the consequences, if it flipped today?” Another woman at the table asked.
“Again, we’re not sure. It would certainly impair many navigational instruments—”
Teresa’s nostrils flared. She’d known this. Yet hearing it said aloud felt like a direct challenge.
“ — and it might eliminate some protection from solar proton storms. Space facilities would need shielding or have to be abandoned altogether.”
“And?” Manella prompted.