When Michael Manerchia's granddaughter pulled a few shards of a yellow plate from the backyard behind his circa-1790s home, she had no idea what she'd found. "We're aware of only three of those plates in existence," said Joseph Blondino, a Ph.D. student studying archaeology at Temple. "People don't realize how vital the town of Marcus Hook was in the founding of this country," said Blondino, who is advising a team of volunteers excavating sites throughout the borough. "Because of its position on the river and the way the river flows, Marcus Hook could have become Philadelphia. Had William Penn not traveled farther upriver and found the land where Philadelphia now is, that could very well have been the case."