Earth is the third planet from the Sun and the only astronomical object known to harbor life. Much of Earth's polar regions are covered in ice. Earth's outer layer is divided into several rigid tectonic plates that migrate across the surface over many millions of years. Earth's interior remains active with a solid iron inner core , a liquid outer core that generates Earth's magnetic field , and a convecting mantle that drives plate tectonics. According to radiometric dating estimation and other evidence, Earth formed over 4. Within the first billion years of Earth's history , life appeared in the oceans and began to affect Earth's atmosphere and surface, leading to the proliferation of anaerobic and, later , aerobic organisms.
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Medieval medicine in Western Europe was composed of a mixture of pseudoscientific ideas from antiquity. In the Early Middle Ages , following the fall of the Western Roman Empire , standard medical knowledge was based chiefly upon surviving Greek and Roman texts, preserved in monasteries and elsewhere. Medieval medicine is widely misunderstood, thought of as a uniform attitude composed of placing hopes in the church and God to heal all sicknesses, while sickness itself exists as a product of destiny , sin , and astral influences as physical causes. On the other hand, medieval medicine, especially in the second half of the medieval period c. Medieval medicine attributed illnesses and disease, not to sinful behaviour, but to natural causes, and sin was only connected to illness in a more general sense of the view that disease manifested in humanity as a result of its fallen state from God.
Various terms are used for passenger railway lines and equipment; the usage of these terms differs substantially between areas:. It uses passenger railcars operating singly or in multiple unit trains on fixed rails. It operates on separate rights-of-way from which all other vehicular and foot traffic are excluded i. It uses sophisticated signaling systems , and high platform loading.