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The term reflection is loose, and considered by some an abuse of language, with inversion preferred; however, point reflection is widely used. Such maps are involutions, meaning that they have order 2 – they are their own inverse: applying them twice yields the identity map – which is also true of other maps called reflections.
The first eon in Earth's history, the Hadean, begins with Earth's formation and is followed by the Archean eon at 3.8 Ga. [2]: 145 The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga, [34] [35] [36] soon after the formation of Earth's crust and Earth itself.
During the Permian all Earth's major landmasses, except portions of East Asia, were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ( Panthalassa , the universal sea ), and the Paleo-Tethys Ocean , a ...
This questioning represented a turning point in the study of the Earth. It was now possible to study the history of the Earth from a scientific perspective without religious preconceptions. With the application of scientific methods to the investigation of the Earth's history, the study of geology could become a distinct field of science.
Earth is the third planet from the Sun and the only astronomical object known to harbor life. [23] This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust.
Crustal studies – investigation into the structure and origin of the Earth's crust, through to the Moho discontinuity and beyond, at depths of up to 100 km. A method similar to reflection seismology which uses electromagnetic instead of elastic waves, and has a smaller depth of penetration, is known as Ground-penetrating radar or GPR.
The asteroid that killed most dinosaurs 66 million years ago left behind traces of its own origin.. Researchers think they know where the Chicxulub impactor came from based on levels of ruthenium ...
In refraction seismology, direct wave (blue) arrive the receivers first, followed by headwave (red). The point where the direct wave and headwave meet is known as the crossover point. Reflection Seismology: Seismic reflection capitalizes on the echo of seismic waves off boundaries where acoustic impedance varies between earth layers. [81]