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Apart from the Late Heavy Bombardment, events on other planets probably had little direct influence on the Earth, and events on Earth had correspondingly little effect on those planets.
Construction of a time scale that links the planets is, therefore, of only limited relevance to the Earth's time scale, except in a Solar System context.
In East Asia and Siberia, the same unit is split into Alexian, Atdabanian, and Botomian stages.
A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology and define universal horizons that can be used around the world.
The first three of these can be referred to collectively as the Precambrian supereon.
Eons are divided into eras, which are in turn divided into periods, epochs and ages.
The existence, timing, and terrestrial effects of the Late Heavy Bombardment is still debated.
In Ancient Greece, Aristotle (384-322 BCE) observed that fossils of seashells in rocks resembled those found on beaches – he inferred that the fossils in rocks were formed by living animals, and he reasoned that the positions of land and sea had changed over long periods of time.
Dominantly fluid planets, such as the gas giants, do not preserve their history in a comparable manner.
For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous–Paleogene extinction event, which marked the demise of the non-avian dinosaurs and many other groups of life.
Older time spans, which predate the reliable fossil record (before the Proterozoic eon), are defined by their absolute age.
Leonardo da Vinci (1452–1519) concurred with Aristotle's interpretation that fossils represented the remains of ancient life.
The 11th-century Persian geologist Avicenna (Ibn Sina, died 1037) and the 13th-century Dominican bishop Albertus Magnus (died 1280) extended Aristotle's explanation into a theory of a petrifying fluid.