Jellyfish have lived in Earth's oceans for over 500 million years, making them older than both dinosaurs and trees.

Jellyfish belong to the phylum Cnidaria, a group of animals that first appeared in the fossil record during the Cambrian Period roughly 505 to 540 million years ago. Fossil evidence from the Marjum Formation in Utah and the Burgess Shale in Canada confirms that complex jellyfish were already swimming in the seas long before the first land plants appeared 470 million years ago. For comparison, the first dinosaurs did not emerge until the Triassic Period about 230 to 245 million years ago.Their incredible longevity is attributed to their simple but effective biological design. Jellyfish are composed of about 95% water and lack a centralized nervous system, instead using a decentralized 'nerve net' to sense their surroundings. This minimal biological requirement allows them to survive in low-oxygen environments where other marine life would perish. They are also prolific breeders, with some species capable of releasing thousands of eggs daily.Modern research from the Smithsonian Institution highlights how jellyfish populations are currently booming due to human-induced changes in the ocean. As overfishing removes their natural predators and competitors, and agricultural runoff creates 'dead zones' with low oxygen, jellyfish are filling the ecological void. Their ability to adapt to rising water temperatures and increased acidity makes them one of the few winners in the face of global climate change.