From my notebook.
The Earth is divided into a core, mantle and crust. The core, hot and iron-rich, consists of a solid inner and liquid outer core. Convection in the outer core creates the magnetic field. The upper mantle and crust constitute the lithosphere, broken up into tectonic plates that ride the asthenosphere, a viscous region of the upper mantle. The science of this movement, plate tectonics, developed in the mid-twentieth century, superseding the idea of continental drift.
71% of the Earth’s surface is covered by water. 97.5% of this water is saline. Of the 2.5% fresh water, 68.7% is ice. The Sun drives the water cycle, a continuous exchange of water within the hydrosphere through evaporation, condensation, precipitation, infiltration and runoff. The gravitational force of the Moon and Sun cause tides, the cyclic rising and falling of the ocean surface. Most places experience a semidiurnal tide: two high and low tides a day. A diurnal tide is one high and low tide a day. The Earth has five oceans: the Pacific, Atlantic, Indian, Southern and the Arctic. The planet experiences periodic ice ages which include colder glacial and warmer interglacial periods. It is currently in an interglacial period of an ice age known as the Quaternary glaciation. The most recent glacial period of this ice age was the Last Glacial Maximum 20 ka.
Earth has had three atmospheres. The first was helium and hydrogen; the second carbon dioxide and water vapour from volcanic outgassing and bolide collisions. The water condensed into oceans. Photosynthesis created the third atmosphere, consisting mostly of nitrogen, oxygen and argon. The atmosphere is divided into the troposphere, stratosphere, mesosphere, thermosphere and exosphere. Most weather occurs in the troposphere. The stratosphere contains the ozone layer, which absorbs ultraviolet light. The mesosphere is where most meteors burn up. The thermosphere includes the Kármán line, the working definition for the boundary between the atmosphere and space, 100km above the Earth’s surface. The sky appears blue due to the atmosphere scattering sunlight, a phenomenon called Rayleigh scattering.
The increasing luminosity of the Sun will end most plant life within the next 600 million years. In 1.1 billion years, the oceans will evaporate. In five billion years the Earth will be swallowed by the Sun.
Scholars in the Western world have known that the Earth is round since the ancient Greeks.