As terrestrial creatures, humans are largely unaware that much of life's history has taken place in the ocean. Indeed, life had been evolving and changing for more than 3 billion years—the majority of the planet's existence—before the first creatures made their way out of the water.

At Smithsonian Ocean, we have lesson plans, activities, and resources to help you engage your students in the wonders of our oceans.

They tell not only an evolutionary story — the family tree of life — but also how these creatures used to live. Fossils can be found throughout the geologic history of earth , going back billions of years.

Evidence shows that life probably began in the ocean at least 3.5 billion years ago. Photosynthesis began more than 2.5 billion years ago—the Great Oxidation Event. But it took hundreds of millions of years for enough oxygen to build up in the atmosphere and ocean to support complex life.

Scientists, such as paleontologists Louis Jacobs, Michael J. Polcyn and their team at Southern Methodist University, along with scientists in Angola, Portugal and the Netherlands, study the opening of the South Atlantic Ocean and its effect on ancient life.

“She sells sea shells by the sea shore.” Remember this grade school tongue-twister? What you probably didn’t know is that this nursery rhyme is based on a real person who not only sold seaside curiosities by the seashore, but became world renowned for her fossil discoveries.

Anatomy, Diversity, and Evolution Anatomy. Numerous characteristics are unique to the coelacanth among living fishes. Among them is the presence of a "rostral organ" in the snout that is part of the electrosensory system, and an intracranial joint or "hinge" in the skull that allows the anterior portion of the cranium to swing upwards, greatly enlarging the gape of the mouth.

In 2022, researchers finally tracked a group of migrating eels to the middle of the Atlantic Ocean in an area known as the Sargasso Sea. The mystery of the eel can be traced back to ancient times when the Egyptians told of how the eels sprang up from the Nile at the warming of the sun.

Though they largely live in the deep ocean today, during the Cambrian through the Permian, crinoid forests covered parts of the seafloor. Known as sea lilies for their beautiful, feathered arms, these creatures are cousins of modern sea stars and sea urchins.

The megalodon was a fearsome predator. As the largest predator of the time, it ate a diverse array of prey including toothed and baleen whales, seals, sea cows, and sea turtles. As an opportunist, it also likely ate fish and other sharks.