1. Climate change would be catastrophic. The oceans help regulate the Earth's temperature by absorbing and releasing heat. Without them, the Earth would be much hotter and drier, making it difficult or impossible for most plants and animals to survive.

2. The atmosphere would be much thinner. The oceans release oxygen into the atmosphere, and they also absorb carbon dioxide. Without them, the atmosphere would be thinner, with less oxygen and more carbon dioxide, making it difficult for most animals and plants to breathe.

3. The continents would be much larger. The oceans cover about 71% of the Earth's surface, so without them, the continents would be much larger and more connected. This would change the climate of the remaining landmasses, making some areas more humid and others more arid.

4. The water cycle would be disrupted. The oceans play a crucial role in the water cycle by evaporating water and transporting it to land. Without them, the water cycle would be disrupted, leading to droughts in some areas and flooding in others.

5. Many species would go extinct. The oceans are home to a vast array of marine life, including fish, whales, dolphins, and sea turtles. Without them, these species would all go extinct.

6. The human population would be decimated. The oceans are a source of food, water, and transportation for humans, and they also play a role in regulating the climate. Without them, the human population would be decimated.

Overall, the disappearance of the oceans would be a catastrophic event for life on Earth, leading to the end of most plant and animal species and the decimation of the human population.