(4.54 billion years), which is the beginning of the informally recognized Hadean eon – a division of geologic time.
Geology describes the structure of the Earth beneath its surface, and the processes that have shaped that structure.
It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of those rocks.
Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core.
These advances led to the development of a layered model of the Earth, with a crust and lithosphere on top, the mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that.
) is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time.
Geology can also refer to the study of the solid features of any terrestrial planet or natural satellite, (such as Mars or the Moon).Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, and numerical modelling.In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, and providing insights into past climate change.The specimens can be tested for: In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, solid, upper mantle, which is called the asthenosphere.This theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.Geology, a major academic discipline, also plays a role in geotechnical engineering.