# How to measure the temperature in ancient times

“Little brothers can’t just talk about grace, forget temperature, and wear thicker.” The temperature in the sentence is a physical quantity that indicates the degree of heat and cold of an object. Microscopically, it is the intensity of thermal motion of an object’s molecules. From the ice bottle invented in ancient China to the thermometer invented by Galileo, the generation of thermometers laid the foundation for the development of thermodynamics and thermal science.

As early as the 2nd century BC, the ancient Chinese began to make thermometers using the simplest and most readily available water as a medium, and called it an “ice bottle.” It judges the temperature through the freezing and melting of water. At the time of the Shang and Zhou Dynasties, the ancients began to observe the “fire”, guessing the temperature by the change of flame during combustion, and applying the method of visual inspection to the smelting of bronze. In the pre-Qin Dynasty, “Kaogong Ji Li Shi” records the methods and processes of observing the fire. Different flames and smoke changes represent different temperatures. For example, white smog appears in the smelting of bronze, indicating that the temperature is about 907 ° C, zinc begins to volatilize; the furnace fire is pure blue, indicating that the temperature has reached 1200 ° C, zinc is completely volatilized; all of the copper green flame, indicating that it can be cast at this time. After modern scientific verification, the visual test method is quite accurate, and it is still used in many industries such as modern smelting and porcelain making.

With the strong development of Western technology and the in-depth study of geology, it is possible to measure the temperature in ancient times. Scientists tell us that if we can find traces of temperature changes during geological history, we can know the temperature at that time. Thus, people started with geochemical oxygen isotopes and finally found another reliable way to measure the temperature in ancient times. Oxygen is a large family including oxygen 16, oxygen 17, and oxygen 18. Among them, the nuclear reaction capacity of oxygen 18 greatly exceeds that of oxygen 16 and oxygen 17, but its amount is particularly rare. According to statistics, in nature, an oxygen 18 is produced for every 500 oxygen atoms formed. The ratio of oxygen isotope changes with temperature. When organisms are alive, the ratio of oxygen isotope in their bodies has a certain relationship with the temperature of the environment in which they live. When these organisms die, the ratio of such isotopes in their bodies no longer changes. After hundreds of millions of years, the remains of these organisms have become fossils. People can chemically extract oxygen from fossils and measure the ratio of oxygen 16 to oxygen 18 to know the temperature of the living environment of these organisms. You see, the ratio of oxygen isotope is really a sensitive thermometer.

In addition, when observing the ocean core, the scientists found that there is a roundworm that is particularly sensitive to changes in cold and warm, and calculating the ratio of the number of the roundworms to the total number of foraminifera can be used to derive the ocean temperature at that time. The calculations show that the high ratio is related to the warm water during the glacial period, and the low ratio is related to the cold water during the glacial period. More interestingly, the direction of the spiral of the screw shell is also related to temperature. The shell of the right-handed truncated cone is related to the warm environment, and the left-handed shell is related to the colder environment. Therefore, the temperature of the Pangu period can be inferred from the ratio of the spiral shell to the left and right.

The paleoclimate and paleoenvironment data obtained by detecting the temperature in ancient times can provide a predictive basis for future climate and environmental changes, and can also provide effective scientific ideas for explaining the causes of today’s climate change.