Why is the Earth blue?

The greenhouse effect and plate tectonics are essential for maintaining water on the Earth’s surface..
The greenhouse effect and plate tectonics are essential for maintaining water on the Earth’s surface..
(Image: © NASA/Goddard Space Flight Center/Reto Stöckli, CC BY)

This article was originally published at The Conversation. The publication contributed the article to Space.com’s Expert Voices: Op-Ed & Insights.

Guillaume Paris, Géochimiste, chargé de recherche CNRS au Centre de recherches pétrographiques et géochimiques de Nancy, Université de Lorraine

Laurette Piani, Cosmochimiste, chargée de recherche CNRS au Centre de Recherches Pétrographiques et Géochimiques (CRPG) de Nancy, CNRS, Université de Lorraine

Seen from space, the Earth is blue. The Earth has been blue for over 4 billion years because of the liquid water on its surface. How has the Earth managed to sustain liquid water on its surface for such a long time?

There is only one known planet with permanent bodies of liquid water at its surface: ours. Earth sciences allow us to explain why the Earth has almost always been blue: it’s neither too warm nor too cold. If the Earth was first red and black, it has been blue for more than 4 billion years, with rare exceptions when it got too cold and turned into a white snowball.

This incredible characteristic is due to the interactions of the water cycle with plate tectonics and the greenhouse effect, as well as the configuration of the solar system. Today, Earth’s average surface temperature is about 15°C, colder than Venus (465 °C) and warmer than Mars (-60 °C on average). On Earth, at sea level, water freezes below 0°C and boils at 100°C. Earth’s surface is thus kept within a temperature range that might seem large to us, but is actually fairly narrow when compared with other planets, and it has remained so for billions of years.

Interactions with water, plate tectonics and CO₂

The planet we live on is a remarkable place. But have you ever wondered how or why these things occur? How the Earth was made? How we predict the weather? How fossils form? What causes earthquakes or which animals glow in the dark? “Incredible Earth” reveals answers to these questions and more on a thrilling journey through everything you need to know about our world — and with gorgeous photography and insightful diagrams along the way!

How It Works: Book of Incredible Earth 9th Edition / AvaxHome

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Nancy Thames

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