Which supercontinent is believed to have formed about 1.8 billion years ago?

The supercontinent formed about 1.8 billion years ago is Colombia, also known as Nuna. This ancient landmass is significant in geological history because it represents a period when large sections of the continents merged into a single landform. Colombia is believed to have existed during the Proterozoic era, with its formation and assembly being a critical phase in the Earth's tectonic evolution.

Additionally, Colombia played a pivotal role in the assemblage and breakup of several smaller landmasses, leading to changes in oceanic circulation and climate, which had far-reaching effects on the development of life on Earth. While other supercontinents like Rodinia, Ur, and Pannotia occurred at different times in the Earth's history, they do not correspond with the timeline of approximately 1.8 billion years ago, emphasizing Colombia's unique position in the geological timeline.