Age of the Earth in the context of "Thorium-234"

Geology is a branch of natural science concerned with the Earth and other astronomical bodies, the rocks of which they are composed, and the processes by which they change over time. The name comes from Ancient Greek γῆ (gê) 'earth' and λoγία (-logía) 'study of, discourse'. Modern geology significantly overlaps all other Earth sciences, including hydrology. It is integrated with Earth system science and planetary science.

Geology describes the structure of the Earth on and beneath its surface and the processes that have shaped that structure. Geologists study the mineralogical composition of rocks in order to get insight into their history of formation. Geology determines the relative ages of rocks found at a given location; geochemistry (a branch of geology) determines their absolute ages. By combining various petrological, crystallographic, and paleontological tools, geologists are able to chronicle the geological history of the Earth as a whole. One aspect is to demonstrate the age of the Earth. Geology provides evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates.

Uranium is a chemical element; it has symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactively decays, usually by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes, making them useful for dating the age of the Earth. The most common isotopes in natural uranium are uranium-238 (which has 146 neutrons and accounts for over 99% of uranium on Earth) and uranium-235 (which has 143 neutrons). Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead and slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.

Many contemporary uses of uranium exploit its unique nuclear properties. Uranium is used in nuclear power plants and nuclear weapons because it is the only naturally occurring element with a fissile isotope – uranium-235 – present in non-trace amounts. However, because of the low abundance of uranium-235 in natural uranium (which is overwhelmingly uranium-238), uranium needs to undergo enrichment so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is studied for future industrial use in nuclear technology. Uranium-238 has a small probability for spontaneous fission or even induced fission with fast neutrons; uranium-235, and to a lesser degree uranium-233, have a much higher fission cross-section for slow neutrons. In sufficient concentration, these isotopes maintain a sustained nuclear chain reaction. This generates the heat in nuclear power reactors and produces the fissile material for nuclear weapons. The primary civilian use for uranium harnesses the heat energy to produce electricity. Depleted uranium (U) is used in kinetic energy penetrators and armor plating.

Old Earth creationism (OEC) is an umbrella of theological views encompassing certain varieties of creationism which may or can include day-age creationism, gap creationism, progressive creationism, and sometimes theistic evolution.

Broadly speaking, OEC usually occupies a middle ground between young Earth creationism (YEC) and theistic evolution (TE). In contrast to YEC, it is typically more compatible with the scientific consensus on the issues of physics, chemistry, geology, and the age of the Earth. However, like YEC and in contrast with TE, some forms of it reject macroevolution, claiming it is biologically untenable and not supported by the fossil record, and the concept of universal descent from a last universal common ancestor.

Gap creationism (also known as ruin-restoration creationism, restoration creationism, or "the Gap Theory") is a form of creationism that posits that the six-yom creation period, as described in the Book of Genesis, involved six literal 24-hour days (light being "day" and dark "night" as God specified), but that there was a gap of time between two distinct creations in the first and the second verses of Genesis, which the theory states explains many scientific observations, including the age of the Earth. It differs from day-age creationism, which posits that the 'days' of creation were much longer periods (of thousands or millions of years), and from young Earth creationism, which although it agrees concerning the six literal 24-hour days of creation, does not posit any gap of time.

Day-age creationism is an interpretation of the creation accounts in Genesis. It holds that the six days referred to in the Genesis account of creation are not literal 24-hour days, but are much longer periods (from thousands to billions of years). The Genesis account is then reconciled with the age of the Earth. Proponents of the day-age theory can be found among both theistic evolutionists, who accept the scientific consensus on evolution, and progressive creationists, who reject it. The theories are said to be built on the understanding that the Hebrew word yom is also used to refer to a time period, with a beginning and an end and not necessarily that of a 24-hour day.

The differences between the young Earth interpretation of Genesis and modern scientific theories believed by some day-age creationists such as the Big Bang, abiogenesis, and common descent are significant. The young Earth interpretation says that everything in the universe and on Earth was created in six 24-hour days, estimated to have occurred some 6,000 years ago. Modern scientific observations, however, put the age of the universe at 13.8 billion years and the Earth at 4.5 billion years, with various forms of life, including humans, being formed gradually over time.

Progressive creationism is the religious belief that God created new forms of life gradually over a period of hundreds of millions of years. As a form of old Earth creationism, it accepts mainstream geological and cosmological estimates for the age of the Earth, some tenets of biology such as microevolution as well as archaeology to make its case. In this view creation occurred in rapid bursts in which all "kinds" of plants and animals appear in stages lasting millions of years. The bursts are followed by periods of stasis or equilibrium to accommodate new arrivals. These bursts represent instances of God creating new types of organisms by divine intervention. As viewed from the archaeological record, progressive creationism holds that "species do not gradually appear by the steady transformation of its ancestors; [but] appear all at once and "fully formed."

The view rejects macroevolution, claiming it is biologically untenable and not supported by the fossil record, as well as rejects the concept of universal descent from a last universal common ancestor. Thus the evidence for macroevolution is claimed to be false, but microevolution is accepted as a genetic parameter designed by the Creator into the fabric of genetics to allow for environmental adaptations and survival. Generally, it is viewed by proponents as a middle ground between literal creationism and theistic evolution.