Tufa towers made of calcium carbonate, near Mono Lake California. Tufa is a chemical sedimentary rock composed of calcium carbonate, formed by evaporation as a think, surficial, soft, spongy, cellular or porous, semifriable incrustation around the mouth of a hot or cold calcareous spring or seep. It can also form along a stream carrying calcium carbonate in solution, or be precipitated by algae or bacteria.
Oxygen-18 can be used as a proxy measurement of sea surface temperatures. It can also serve as a proxy measurement for precipitation, particularly in areas like the central Pacific where large El Nino Southern Oscillation (ENSO) related oscillations in annual rainfall occur. Coral oxygen-18 is a paleothermometer that enables us to answer important questions about climatic variability in the world's oceans. This core from the Galapagos Islands gives us a 350-year record of sea surface temperatures and, by extension, El Nino activity in the eastern Pacific.
Satellite image showing a sharp air mass boundary taken in June of 2002. This is often a situation where severe thunderstorms can develop. The sunlit anvil tops here are estimated to be over 60,000 feet in altitude.