About 20,000 years ago, Passanageset Park at Broad Meadows Marsh was covered by a mile-high glacier that stretched from the Arctic to Cape Cod. As the glacier slowly advanced and retreated, it scoured and scarred hills of bedrock, pushed up mounds of sand and till, dislodged boulders, left behind ponds and steams of melted ice, and created the basic features that are still visible today. By 11,000 years ago, the first people arrived, taking advantage of the many resources this area had to offer. They moved from place to place, traveling hundreds of miles throughout the year to obtain their food, clothing, tools, and anything else they needed to survive in a cold and changing climate.
After the last glacier retreated from this area, the landscape and climate continued to change. About 3,500 years ago, the shoreline here stabilized, the four seasons became more pronounced, and many of the plants and animals common here today were established. Social changes occurred, too, as groups of people became larger and as families found they did not need to travel so far to get the resources they needed. Trade and exchange networks were established between groups living in different areas. It was during this time that a person or persons in the area buried over 200 maritime-related tools and other implements that were unearthed at nearby Caddy Park during the construction of the playground there in 1999. The First People who settled here, fished here, and had planting fields here did so for thousands of years. The descendants of the First People in this area are known as the Massachusett.