Onboard the Goya, Tolland had now introduced Xavia and Rachel. The ships geologist was looking increasingly baffled by the distinguished entourage standing before her in the hydrolab. In addition, Rachels eagerness to run the tests and get off the ship as fast as possible was clearly making Xavia uneasy.
Take your time, Xavia, Tolland willed her. We need to know everything.
Xavia was talking now, her voice stiff. In your documentary, Mike, you said those little metallic inclusions in the rock could form only in space.
Tolland already felt a tremor of apprehension. Chondrules form only in space. Thats what NASA told me.
But according to these notes, Xavia said, holding up the pages, thats not entirely true.
Corky glared. Of course its true!
Xavia scowled at Corky and waved the notes. Last year a young geologist named Lee Pollock out of Drew University was using a new breed of marine robot to do Pacific deepwater crust sampling in the Mariana Trench and pulled up a loose rock that contained a geologic feature he had never seen before. The feature was quite similar in appearance to chondrules. He called them plagioclase stress inclusions‑tiny bubbles of metal that apparently had been rehomogenized during deep ocean pressurization events. Dr. Pollock was amazed to find metallic bubbles in an ocean rock, and he formulated a unique theory to explain their presence.
Corky grumbled. I suppose he would have to.
Xavia ignored him. Dr. Pollock asserted that the rock formed in an ultradeep oceanic environment where extreme pressure metamorphosed a pre‑existing rock, permitting some of the disparate metals to fuse.
Tolland considered it. The Mariana Trench was seven miles down, one of the last truly unexplored regions on the planet. Only a handful of robotic probes had ever ventured that deep, and most had collapsed well before they reached the bottom. The water pressure in the trench was enormous‑an astounding eighteen thousand pounds per square inch, as opposed to a mere twenty‑four pounds on the oceans surface. Oceanographers still had very little understanding of the geologic forces at the deepest ocean floor. So, this guy Pollock thinks the Mariana Trench can make rocks with chondrulelike features?
Its an extremely obscure theory, Xavia said. In fact, its never even been formally published. I only happened to stumble across Pollocks personal notes on the Web by chance last month when I was doing research on fluid‑rock interactions for our upcoming megaplume show. Otherwise, I never would have heard of it.
The theory has never been published, Corky said, because its ridiculous. You need heat to form chondrules. Theres no way water pressure could rearrange the crystalline structure of a rock.
Pressure, Xavia fired back, happens to be the single biggest contributor to geologic change on our planet. A little something called a metamorphic rock? Geology 101?
Tolland realized Xavia had a point. Although heat did play a role in some of earths metamorphic geology, most metamorphic rocks were formed by extreme pressure. Incredibly, rocks deep in the earths crust were under so much pressure that they acted more like thick molasses than solid rock, becoming elastic and undergoing chemical changes as they did. Nonetheless, Dr. Pollocks theory still seemed like a stretch.
Xavia, Tolland said. Ive never heard of water pressure alone chemically altering a rock. Youre the geologist, whats your take?
Well, she said, flipping through her notes, it sounds like water pressure isnt the only factor. Xavia found a passage and read Pollocks notes verbatim. Oceanic crust in the Mariana Trench, already under enormous hydrostatic pressurization, can find itself further compressed by tectonic forces from the regions subduction zones.
Of course, Tolland thought. The Mariana Trench, in addition to being crushed under seven miles of water, was a subduction zone‑the compression line where the Pacific and Indian plates moved toward one another and collided. Combined pressures in the trench could be enormous, and because the area was so remote and dangerous to study, if there were chondrules down there, chances of anyone knowing about it were very slim.
Xavia kept reading. Combined hydrostatic and tectonic pressures could potentially force crust into an elastic or semiliquid state, allowing lighter elements to fuse into chondrulelike structures thought to occur only in space.
Corky rolled his eyes. Impossible.
Tolland glanced at Corky. Is there any alternative explanation for the chondrules in the rock Dr. Pollock found?
Easy, Corky said. Pollock found an actual meteorite. Meteorites fall into the ocean all the time. Pollock would not have suspected it was a meteorite because the fusion crust would have eroded away from years under the water, making it look like a normal rock. Corky turned to Xavia. I dont suppose Pollock had the brains to measure the nickel content, did he?
Actually, yes, Xavia fired back, flipping through the notes again. Pollock writes: I was surprised to find the nickel content of the specimen falling within a midrange value not usually associated with terrestrial rocks.
Tolland and Rachel exchanged startled looks.
Xavia continued reading. Although the quantity of nickel does not fall within the normally acceptable midrange window for meteoritic origin, it is surprisingly close.
Rachel looked troubled. How close? Is there any way this ocean rock could be mistaken for a meteorite?
Xavia shook her head. Im not a chemical petrologist, but as I understand it, there are numerous chemical differences between the rock Pollock found and actual meteorites.
What are those differences? Tolland pressed.
Xavia turned her attention to a graph in her notes. According to this, one difference is in the chemical structure of the chondrules themselves. It looks like the titanium/zirconium ratios differ. The titanium/ zirconium ratio in the chondrules of the ocean sample showed ultradepleted zirconium. She looked up. Only two parts per million.
Two ppm? Corky blurted. Meteorites have thousands of times that!
Exactly, Xavia replied. Which is why Pollock thinks his samples chondrules are not from space.
Tolland leaned over and whispered to Corky, Did NASA happen to measure the titanium/zirconium ratio in the Milne rock?
Of course not, Corky sputtered. Nobody would ever measure that. Its like looking at a car and measuring the tires rubber content to confirm youre looking at a car!
Tolland heaved a sigh and looked back at Xavia. If we give you a rock sample with chondrules in it, can you run a test to determine whether these inclusions are meteoric chondrules or . . . one of Pollocks deep ocean compression things?
Xavia shrugged. I suppose. The electron microprobes accuracy should be close enough. Whats this all about, anyway?
Tolland turned to Corky. Give it to her.
Corky reluctantly pulled the meteorite sample from his pocket and held it out for Xavia.
Xavias brow furrowed as she took the stone disk. She eyed the fusion crust and then the fossil embedded in the rock. My God! she said, her head rocketing upward. This isnt part of . . . ?
Yeah, Tolland said. Unfortunately it is.