When you look at a picture of Mars next to a picture of Earth, you might notice one big difference: Earth is covered in blue oceans and Mars doesn't seem to have any water at all! But scientists have discovered all kinds of clues that make them think Mars used to have an ocean too! Second Grade Next Generation Science Standards Disciplinary Core Ideas: ESS2.A: Earth Materials and Systems - Wind and water can change the shape of the land (2-ESS2-1). ESS2.C: The Roles of Water in Earth’s Surface Processes - Water is found in the ocean, rivers, lakes, and ponds. Water exists as solid ice and in liquid form (2-ESS2-3). Performance Expectations: 2-ESS2-1 Compare multiple solutions designed to slow or prevent wind or water from changing the shape of the land 2-ESS2-3 Obtain information to identify where water is found on Earth and that it can be solid or liquid.