A speleothem that is being sampled by a microdrill. Because rainwater is slightly acidic, prolonged exposure to rain will chemically erode away limestone rock formations (or even a limestone statue for that matter). Calcium carbonate dissolves when exposed to acids. Limestone rocks are easy to erode compared metamorphic and igneous rocks. When a sedimentary rock is composed dominantly of calcium carbonate, geoscientists call it a limestone. Here we will talk briefly about the most common types of calcite used for isotope analysis.Ĭalcite is a component in many sedimentary rocks. Calcite and calcium carbonate are common on the Earth and in the oceans, and can take several forms. In this formula, there are three elements: calcium (Ca), carbon (C), and three oxygen atoms (O). Paleoclimatologists obtain carbon and oxygen isotopes from calcite, a common variety of calcium carbonate, with the chemical formula CaCO 3. These were formed by dissolved ions carried by groundwater into the cave, where they created new rock formations. How are carbon and oxygen isotopes obtained? Adriane pointing out a type of stalactite called ‘cave curtains’ while caving in western Ireland. Although there are several types of stable isotopes, we will mainly talk about carbon and oxygen obtained from planktic and benthic foraminifera, as these are very common in paleoclimatology (especially to study our oceans), but will also briefly touch on other proxies used for isotope analyses. Two of the most common stable isotopes that are used by geoscientists are those of carbon (C) and oxygen (O). Instead, we use stable isotopes that are not undergoing radioactive decay.

However, paleoclimatologists do not commonly work with these unstable isotopes. Several radioactive isotopes occur naturally, and not all are bad or cause harm to humans. An unstable isotope experiences radioactive decay, where the element will lose energy over time. There are two main types of isotopes that geoscientists use to interpret the ancient Earth: stable and unstable isotopes. Therefore, oxygen 16 has 8 protons and 8 neutrons, oxygen 17 has 8 protons and 9 neutrons, and oxygen 18 has 8 protons and 10 neutrons. Because protons and neutrons are roughly equal in mass, an isotope’s number is equal to the sum of its protons and neutrons. An isotope number is a shorthand representation of its mass. Each isotope of oxygen contains 8 protons, but differs in the number of neutrons. For example, there are three isotopes of the element oxygen (O): Oxygen 16, 17, and 18. Isotopes are elements that contain the same amount of protons, but differ in the number of neutrons in their nuclei. P indicates the number of protons N indicates the number of neutrons.Ĭhemical elements are found in different versions, called isotopes. In the above equation, the (s) indicates a solid material (table salt), whereas the (aq) indicates that these ions are dissolved in an aqueous solution. This forms an aqueous (a water based) solution: Most rocks and fossil-hard parts are made of ionic compounds.įor example table salt, sodium chloride, will dissolve in water forming the positively-charged sodium ion and negatively-charged chloride ion. When a solid dissolves in water, the positive and negative ions break apart and dissociate through the water.

Positive and negative ions will attract each to form solids, some liquids, and some gases. When this happens, the elements become ions. However, various chemical reactions in nature will cause elements to either gain or lose electrons, and the elements become positively or negatively charged. Elements have a charged balance (neither positive or negative) because they have an equal number of electrons and protons. Remember that chemical elements are composed of some number of protons, neutrons, and electrons.

One of the many ways in which paleoclimatologists know past climate and ocean conditions is by using the chemical makeup of rock and fossil specimens.

Ca element neutrons