Laurentia

Laurentia is the ancient geological core of the North American continent. It is a massive continental craton, which is a large and stable block of the Earth's crust. This foundation is much more than just North America. In the past, Laurentia included Greenland and the Hebridean terrane in northwest Scotland. Today, it serves as the solid basement upon which much of the continent rests.

The assembly of Laurentia was a violent and slow process involving many collisions. Between 2.0 and 1.8 billion years ago, the core began to form from six or seven large fragments of Archean crust. The process started when the Slave craton collided with the Rae-Hearne craton. Shortly after, the Rae-Hearne craton collided with the Superior Craton. These large pieces merged with smaller blocks like the Wyoming, Nain, and Superior provinces. These massive collisions created huge mountain ranges, such as the Trans-Hudson orogenic belt. These mountains were likely as large as the modern Himalayas.

Laurentia continued to grow through a process called accretion. Accretion is when new material is added to a growing landmass. For nearly 900 million years, small microcontinents and volcanic island arcs crashed into Laurentia's edges. These pieces were often made of juvenile crust. Juvenile crust is new material formed from fresh magma from the Earth's mantle. Major mountain-building events, or orogenies, helped weld these pieces together. These included the Yavapai orogeny and the Grenville orogeny. The Grenville orogeny, occurring between 1.30 and 0.95 billion years ago, added the Llano-Grenville province to the continent.

Some of the oldest rocks on our planet are found within this structure. In eastern and central Canada, the Canadian Shield exposes much of this ancient rock. The Acasta Gneiss in Canada is 4.04 billion years old. In Greenland, the Istaq Gneiss Complex is 3.8 billion years old. These rocks are often metamorphic or igneous, meaning they were changed by heat or formed from cooling magma. In the United States, these old rocks are often hidden. They are covered by thick layers of sedimentary rocks like limestone, sandstone, and shale. These layers can be over 6,100 meters thick.

Laurentia has been a part of several massive supercontinents throughout Earth's history. One major supercontinent was Rodinia. During the time of Rodinia, Laurentia may have sat directly on the equator. Some scientists believe Laurentia was the core of Rodinia, rotated 90 degrees from its current position. Around 750 million years ago, Rodinia broke apart. Laurentia then briefly joined another supercontinent called Pannotia.

Eventually, Laurentia became an independent continent again, separated from other lands by oceans like the Iapetus Ocean.

During the Ordovician period, Laurentia's environment was very different. The continent was often flooded by shallow, warm, tropical seas. These are known as epicontinental seas, which are seas that cover part of a continent. These waters were not very deep, reaching only about 60 meters at the edges. This warm climate was perfect for sea life. Fossil records of shellfish show that this area was near the equator.

These shallow seas allowed for a massive spike in the number of carbonate shells from marine animals.

As time moved forward, Laurentia continued to merge with other landmasses. By the end of the Silurian, Laurentia fused with Baltica and Avalonia. This new combined landmass was called Laurussia.

Later, during the Carboniferous and Permian periods, Laurussia fused with Gondwana. This massive merger created the supercontinent known as Pangaea. This long history of collisions and mergers shows how the solid ground of our modern world was built piece by piece over billions of years.