​When Boston Harbor was dry land, mastodons roamed. Tusked and shaggy, they foraged along a coastal plain that ended as sedimentary sludge eleven miles east of present-day Long Wharf. They wound their trunks around spruce branches and tugged sharply to dislodge a repast of sweet needles, unaware that their vast boreal habitat would soon be supplanted by sun-loving hardwoods. Occasionally, the beasts glanced up at a nearby drumlin. One could never be too careful of the growing bands of humans who so often lurked behind boulders, lying in ambush with fire and spears.

​Such was Massachusetts ten thousand years ago, a land of warming climate and rising seas, home to megafauna on the brink of extinction. For the past million years, Earth had experienced dramatic climatic changes. Temperatures fluctuated, plunging the planet into ice ages interspersed with warmer periods. The most recent Ice Age – through which we are living today – began twenty-five thousand years Before Present (BP). Long winters and cool summers created a snowpack that eventually compacted into an ice sheet stretching from the Arctic to present-day New Jersey. At its maximum extent, the ice contained 5% of the planet’s water, lowering ocean levels by hundreds of feet. As the glaciers expanded and moved, they accumulated silt, pebbles, and boulders. These sediments were deposited when the glaciers began to melt around 18,000 BP, leaving a stony landscape of glacial features familiar to Bostonians today: moraines (Cape Cod), drumlins (the Harbor Islands, Bunker and Beacon Hills), and kettle ponds (Walden Pond), among others. By 14,000 BP, the ice sheet had completely receded from Massachusetts. What remained was a treeless, frigid tundra whose coastline would gradually disappear beneath waves of glacial meltwater.    

As vegetation returned to the region, animals and ancient humans arrived as well. Paleo-Indians and their Archaic Period descendants (8,000-3,000 BP) settled along the coastline and rivers, where they enjoyed abundant fish, shellfish, and game. Over time, they transitioned from living in small bands to inhabiting villages. Archaic peoples led a hunter-gatherer lifestyle, migrating seasonally between hills and lowlands, forests and estuaries to secure food and supplies. They built canoes and fish weirs from wood, carved harpoons and awls from bone, and chiseled arrow and spear points, knives, pestles, and gaming pieces from stone. They wove baskets and decorated animal hide clothing with beads. Archaic peoples were deeply familiar with the Boston-area landscape and waterways. Such knowledge enabled Boston-area inhabitants to survive and thrive.

​Archaeologists have identified many Archaic settlements throughout Boston. The Harbor Islands, popular fishing and clam digging sites, are littered with artifacts, from net weights to jewelry. In 1913 and the 1940s, subway construction workers unearthed four thousand-year-old fish weirs along Boylston Street, a former wetland. Later, in 1982, archaeologists discovered hearths, earthen pits, and various artifacts associated with hunting, stone tool production, and food preparation near the Charlestown Navy Yard – relics of three temporary occupation sites spanning the years between 5000 and 1,200 BP. This period witnessed the transformation of local Native civilization. Plants became a dietary staple to such an extent that villages began to develop agricultural practices. Emerging long-distance trade routes supplied people with goods from as far away as the Hudson River and, perhaps, the Great Lakes. Women used glacial deposits of clay to create ceramics, refining their artistry in ways that enable today’s archaeologists to date excavation sites by analyzing the pottery they contain. These dramatic developments in Northeast American civilization marked the transition from the Archaic to Early Woodland Periods. They gave rise to modern Native tribes and set the stage for the cultural and economic conditions that Europeans encountered when they first set foot in Massachusetts four hundred years ago.

Imagine a world where South America is at the South Pole, Siberia, along the Tropic of Capricorn, and Greenland, at the Equator. In this world, Florida is a frigid strip of coast connecting South America and Africa. Canada bakes beneath a bright equatorial sun. The rest of North America is a scuba-diver's paradise – assuming scuba-divers numbered among the primitive, single-cell organisms that existed 550 million years ago.
​
Welcome to the Late Precambrian, an era of dramatic geological change and the beginning of New England’s story. At this point, the earth was 3.5 billion years old. It had already experienced multiple episodes of continental drift, volcanism, and glaciation. The Grenville Mountain chain, formed during an earlier period of tectonic collision, had eroded. All that remained was a small layer of bedrock and a large amount of sediment that would eventually become western Massachusetts. Three major continents contained most of the planet’s land mass: Laurentia, Baltica, and the supercontinent Gondwana, whose coastline roiled with volcanic activity. The earthquakes and lava flows were symptoms of tectonic subduction (when one tectonic plate dives beneath another) and rifting (when two plates diverge). Over time, these subterranean stirrings formed the Avalon mountain range and Boston Rift Basin off the coast of present-day South America. We now call this region New England. 

​As Earth entered the Cambrian Period, Avalon broke away from Gondwana. Sediments filled the rift basin and compressed into the Cambridge Argillite and Roxbury Conglomerate (puddingstone) rock formations underlying Greater Boston today. Between 430 and 390 million years ago, Avalon collided with Laurentia, forming the Northern Appalachians. This period of tectonic uplift coincided with rising oxygen levels and an explosion of multicellular life. Complex organisms spread across the globe as New England rose from the depths of the ocean.

​Over the succeeding eons, the planet’s crust continued to transform. The continents collided again 250 million years ago to form Pangaea, lifting the Appalachians to Himalayan heights, and then separated fifty million years later. This period of rifting created today’s continents and instigated more lava flows. We can still see evidence of this geological turbulence in the igneous and metamorphic rocks of Worcester County.

​Volcanic activity subsided as the continents drifted to their present locations. Massachusetts was thereafter shaped by deposition, weathering, and erosion. Temperatures rose, fell, and rose again, causing frequent glaciations that carved the Northeastern bedrock. Meanwhile, life evolved. The region was alternately submerged in shallow seas teeming with crustaceans and fish, and raised high and dry, a coastal forest where dinosaurs roamed. By the time Homo sapiens arrived in New England twelve thousand years ago, the region was a frozen tundra. The latest Ice Age scarred the landscape with eskers, dimpled it with kettle ponds, and pimpled it with erratics – a rugged topography that determined where humans settled, and upon which they would eventually unleash their transformative might. ​