Abundance of the chemical elements of the volatile elements hydrogen, helium, neon, and nitrogen, as well as carbon which has been lost as volatile hydrocarbons. The remaining elemental composition is roughly typical of the "rocky" inner planets, which formed in the thermal zone where solar heat drove volatile compounds into space. The Earth retains oxygen as the second-largest component of its mass (and largest atomic-fraction), mainly from this element being retained in silicate minerals which have a very high melting point and low vapor pressure. The mass-abundance of the nine most abundant elements in the Earth's crust is approximately: oxygen 46%, silicon 28%, aluminum 8.2%,
Boiling Springs, Pennsylvania year round. This is arguably the most intensely fished section of water in Pennsylvania when the White Mayfly hatches. Limestone bedrock streams are rich in minerals, which serve as the basis for the trout's food chain and contribute to healthy growth rates for trout. Boiling Springs and South Middleton Township, which are near the halfway point of the Appalachian Trail, were designated Pennsylvania's first Appalachian Trail Community. In 2010, the Appalachian Trail Conservancy started recognizing towns near the trail that are assets to hikers and the trail. As of 2012, Boiling Springs is one of 23 designated Appalachian Trail Communities.