Jupiter, Saturn, Uranus and Neptune are referred to as the Jovian Planets, or planets that are essentially big balls of gas, each are surrounded by many moons and rings.
Unlike Terrestrial Planets like the Earth, these planets lack solid surfaces and they have relatively small, dense cores that are surrounded by layers of gas, which is made mostly of hydrogen and helium.
Jupiter and Saturn is different from Uranus and Neptune because the first pair is made almost entirely of hydrogen and helium and some hydrogen compounds, while the latter pair are made primarily of hydrogen compounds with smaller traces of hydrogen, helium, metal and rock.
As for the planets' interior, both Jupiter and Saturn have layers of metallic, liquid and gaseous hydrogen extending outward, topped with a layer of visible clouds.
On the other hand, Uranus and Neptune have cores of rock, metal, water, methane and ammonia. The layer surrounding the core is also made up of hydrogen that is covered with a layer of visible clouds.
Water erosion is the main cause which is the loss of topsoil due to water.
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