Scientists now understand most of what has happened on Earth in past eons — Ice Ages, earthquakes, volcanic eruptions, floods, etc. The answers lie in the following methods.

Relative dating is the science of determining the relative order of past events (i.e., the age of one object compared to another), without necessarily determining their absolute age. In geology, rock or superficial deposits, fossils, and the description of a rock’s physical characteristics can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating, which provided a means of absolute dating in the early 20th century, archaeologists and geologists used this technique to determine ages of materials.

The regular order of occurrence of fossils in rock layers was discovered around 1800 by William Smith. While digging the Somerset Coal Canal in southwest England, he found that fossils were always in the same order in the rock layers. As he continued his job as a surveyor, he found the same patterns across England. He also found that certain animals were in only certain layers, and that they were in the same layers all across England. Due to that discovery, Smith was able to recognize the order in which the rocks were formed. Sixteen years after his discovery, he published a geological map of England showing the rocks of different geologic eras.

Absolute dating is the process of determining an age on a specified chronology, in archaeology and geology. Absolute dating provides a numerical age or range, in contrast with relative dating, which places events in order without any measure of the age between events.

In archaeology, absolute dating is usually based on the physical, chemical, and life properties of the materials of artifacts, buildings, or other items that have been modified by humans and by historical associations with materials, with known dates (e.g., coins and written history). Techniques include tree rings in timbers, radiocarbon dating of wood or bones, and trapped charge dating methods such as thermoluminescence dating of glazed ceramics. Coins found in excavations may have their production date written on them, or there may be written records describing the coin and when it was used, allowing the site to be associated with a particular calendar year.

In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young to systems such as uranium-lead dating that allows acquisition of absolute ages for some of the oldest rocks on earth.

Dendrochronology, or tree-ring dating, is the scientific method of dating based on the analysis of patterns of tree rings, also known as growth rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year. In some areas of the world, it is possible to date wood back a few thousand years, or even many thousands. Currently, the maximum for fully anchored chronologies is a little over 11,000 years from the present.

Dendrochronology has three main areas of applications: paleoecology, where it is used to determine certain aspects of past ecologies (most prominently climate); archaeology, where it is used to date old buildings, etc.; and radiocarbon dating, where it is used to calibrate radiocarbon ages.

With regard to Ice Ages, there are three main types of evidence: geological, chemical, and paleontological.

Geological evidence for Ice Ages comes in various forms, including rock scouring and ice cores. Early theories about glaciation assumed that the glacials (the Ice Ages themselves) were short compared to the long inter-glacials (the time between glacials). The advent of sediment and ice cores revealed the true situation: glacials are long, inter-glacials short.

The chemical evidence mainly consists of variations in the ratios of isotopes in fossils present in sediments and sedimentary rocks, and in ocean sediment cores. However, this evidence can be confounded by other factors recorded by isotope ratios.