The laser drilling head was lowered on five hundred feet of minute cable, which had tremendous tensile strength. The vaporized moon substance boiled out of the hole and condensed above the surface, settling as fine dust. As the hole deepened, the condensation products coated the upper portions of the hole and the cable. To keep the hole from thus being closed, the cable was vibrated at a frequency that shook loose the condensing rock products, and the laser head was raised with beams shooting upward to clear the hole. Jim found that a very special technique was required to raise and lower the head at the proper intervals to keep the hole clear and prevent loss of the drilling head. A spare was carried, but he didn't want to face the loss of even one. After three weeks, he felt confident in his operation and began lowering the drilling head to depths of two hundred and three hundred feet. As he had expected, along with the lunar geologists who were participating, the moon showed a definite pattern of stratification. But the differences between the layers seemed slight. Chalky, calcium compounds were abundant. Some were powdery; others were pressed into brittle limestone formations. No really hard rocks such as granite were encountered, however. The boundaries between layers were ill-defined. No one knew what to make of it. The observations were interesting. Explanations were wholly lacking. Then, after five weeks of probing, on the edge of the four-hundred-foot level, Jim found something new. He sought out Sam at the end of the day. "A few years ago," he said, "scientists were startled to find chemicals that were the product of life, inside meteors from outer space." "I understand they've even found bacteria which they have been able to bring to life," said Sam. Jim nodded. "More than four hundred feet deep on the moon I've found the same kind of chemicals--hydrocarbons that must be the product of living cells." "Four hundred feet deep on the moon--" said Sam musingly. "And maybe the moon came from billions of billions of light years across space. So wherever it came from there was something living. What is it? Traces of bacteria, or chemical remains of plant life like our coal mines?" Jim shook his head. "I don't know yet. I'm not sure we can find out until we go there. But, as you say, it means the moon was once the scene of life--wherever it came from." "One thing I haven't understood," said Sam, "is why the moon stopped here if it had been traveling through space for so long. Why didn't it keep on going?" "It was just a combination of factors," said Jim. "The moon happened to be traveling at just the right speed. The earth was in just the right place at the right time. As a result, the moon fell into an orbit around the earth. Pure accident." "A lucky accident!" said Sam.