Short answers, pulled from the story.
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. It describes the structure of the Earth on and beneath its surface and provides evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates.
Georgius Agricola, who lived from 1494 to 1555, is seen as the founder of geology as a scientific discipline. He published his groundbreaking work De Natura Fossilium in 1546.
The word geology was first used by Ulisse Aldrovandi in 1603, then by Jean-Andre Deluc in 1778, and was introduced as a fixed term by Horace-Benedict de Saussure in 1779. It derives from the Greek ge, meaning earth, and logos, meaning speech.
The three major types of rock are igneous, sedimentary, and metamorphic. Igneous rock solidifies from melt, sedimentary rock forms from weathered material that is redeposited and lithified, and metamorphic rock forms when heat and pressure change a rock's mineral content.
Geologists use radioactive isotopes to determine the absolute age of rock samples, a capability that emerged at the beginning of the 20th century. The most suitable isotope systems include uranium-lead, rubidium-strontium, and potassium-argon, while radiocarbon dating is used for geologically young materials containing organic carbon.
The Earth is known to be approximately 4.5 billion years old, with its formation dated to 4.54 billion years ago at the beginning of the Hadean eon. By the early 20th century, radiometric dating had first estimated the Earth's age at two billion years.
Plate tectonics is the theory, discovered in the 1960s, that the Earth's lithosphere is separated into tectonic plates that move across the asthenosphere, coupled to the convection of the mantle. It provided the mechanism for Alfred Wegener's theory of continental drift and is described as a grand unifying theory of geology.