What lunar feature formed on the Moon after lava flowed and smoothed over craters?

• A. Highlands
• B. Craters
• C. Rilles
• D. Marias

Answer: (D)

Lunar maria are the smooth, dark plains formed when basaltic lava welled up and flooded large impact basins on the Moon. As the lava pooled into these basins and cooled, it buried and smoothed over many older craters, leaving broad, flat surfaces that contrast with the rugged, bright highlands. The highlands are the older, heavily cratered regions that remained when lava didn’t flood those areas. Rilles are long trenches or channels formed by lava tubes or tectonic forces, not the broad smoothing of craters by lava flows. Craters are created by impacts, not by lava smoothing. So the smooth, lava-filled plains that formed after lava flowed over craters are the maria.