Because the moon is rotating on its own axis and orbiting around the earth at the same time.
The appearance of fossils would the the answer.
Although there has been some scientific debate about what fossil strata should mark the beginning of this period, the "International Geological Congress" determined that the Cambrian period was approximately 543 million years ago of which the first appearance in the fossil record of worms that made horizontal burrows was discovered.
What looks like fluffy ball?
WHAT DOES?
Answer is thorax...
Hope it helps you...
