Middle Island Sinkhole

December 2023

Pretend to be a time traveler today and get a glimpse of the mysterious sinkholes at Thunder Bay National Marine Sanctuary. Sinkholes are like a time capsule, taking us back to how Earth may have appeared approximately 2.5 billion years ago, at the beginning of the Proterozoic Eon. The water in the Middle Island Sinkhole is rich in sulfur and low in oxygen, making it a great proxy for life on Earth billions of years ago. Since the sinkholes within this Great Lakes national marine sanctuary were discovered in 2002, scientists from around the world have collaborated with the sanctuary to research this time capsule. Here, chemosynthetic bacteria form different colored algal mats that are being studied by biologists and chemists to understand what life might have been like for the mat-like organisms that inhabited Earth long before dinosaurs and humans ever did. Scientific scuba divers collect core samples of the algal mats and sediment in the area for research partners to investigate further.