A round, moving Earth
In the 3rd century BCE Eratosthenes is said to have estimated Earth's circumference remarkably well from the different noon shadows in two Egyptian cities on the same day. For centuries people believed Earth was the centre of the universe, but in 1543 Nicolaus Copernicus published the heliocentric view that Earth is a planet orbiting the Sun, and through Kepler, Galileo and Newton Earth's place in the Solar System was established. The Sun's gravity holds Earth in orbit, and because Earth spins tilted by about 23.4°, we have seasons.
Deep time and Earth's interior
In 1788 James Hutton, observing slow deposition and erosion of rock, argued that Earth's history is unimaginably long, and Charles Lyell systematised this in Principles of Geology (1830). In 1956 Clair Patterson used lead isotopes in meteorites to date Earth at about 4.55 billion years. Zircon crystals about 4.4 billion years old from Australia suggest that continental crust and water may have existed very early. The most widely accepted idea for the Moon's origin is a giant impact of a Mars-sized body with the young Earth. Earth's interior is studied with earthquake waves: beneath the crust lie a thick mantle, a liquid outer core and a solid inner core, whose existence Inge Lehmann of Denmark deduced from seismic waves in 1936. Flowing liquid iron in the outer core generates Earth's magnetic field, which deflects the solar wind and produces aurorae.
Moving continents and a living planet
In 1912–15 Alfred Wegener proposed continental drift, citing matching coastlines and fossils, but could not explain the driving force, so the idea was long rejected. In the 1960s Harry Hess's sea-floor spreading and Vine and Matthews's magnetic stripes on the ocean floor established plate tectonics. Earth's surface is divided into plates moving a few centimetres a year, with earthquakes and volcanoes concentrated at their edges. Earth's distance from the Sun allows liquid water, and its atmosphere and magnetic field shield life. It is the only known inhabited world, yet human activity — through climate change and biodiversity loss — is reshaping its environment; a proposal to name a new epoch, the Anthropocene, was debated, though in 2024 geologists declined to adopt it formally.
FAQ
- Is the Earth a perfect sphere?
- No. Its spin makes it bulge slightly at the equator, forming an oblate spheroid; the equatorial radius is about 21 km longer than the polar radius.
- Is Earth's rotation slowing?
- Yes. Tidal effects of the Moon very gradually lengthen the day, by an estimated 1–2 milliseconds per century.
Sources reviewed: 2026-10-26
References
- Copernicus, N. (1543). De revolutionibus orbium coelestium. Nuremberg: J. Petreius.
- Hutton, J. (1788). Theory of the Earth. Transactions of the Royal Society of Edinburgh, 1, 209–304.
- Lyell, C. (1830). Principles of Geology, Vol. 1. London: John Murray.
- Wegener, A. (1915). Die Entstehung der Kontinente und Ozeane. Braunschweig: Vieweg.
- Lehmann, I. (1936). P′. Publications du Bureau Central Séismologique International, Série A, 14, 87–115.
- Hess, H. H. (1962). History of ocean basins. In A. E. J. Engel et al. (Eds.), Petrologic Studies: A Volume in Honor of A. F. Buddington (pp. 599–620). New York: Geological Society of America.
- Vine, F. J., & Matthews, D. H. (1963). Magnetic anomalies over oceanic ridges. Nature, 199, 947–949.
- Patterson, C. (1956). Age of meteorites and the earth. Geochimica et Cosmochimica Acta, 10(4), 230–237.
- Canup, R. M., & Asphaug, E. (2001). Origin of the Moon in a giant impact near the end of the Earth's formation. Nature, 412, 708–712.
- Wilde, S. A., Valley, J. W., Peck, W. H., & Graham, C. M. (2001). Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature, 409, 175–178.