When did Earth form and how long did its assembly take?
Earth formed by accretion around 4.568 billion years ago, with the primordial Earth's assembly taking between 10 million and 100 million years to complete.
Questions about Land
Short answers, pulled from the story.
What created Earth's early atmosphere and oceans according to scientists?
Volcanic activity and outgassing created Earth's early atmosphere and oceans while asteroids, protoplanets, and comets delivered additional water and ice.
Who first hypothesized continental drift in 1912 and what is it called today?
Alfred Wegener first hypothesized continental drift in 1912 before researchers developed his idea throughout the 20th century into the accepted theory of plate tectonics.
How much precipitation do deserts receive per year and what percentage of land area do they cover?
Deserts have an arid climate receiving less than 25 centimeters of precipitation per year and make up around one fifth of Earth's land area.
When did humans cross from Siberia to Alaska and settle in the Americas?
Fourteen thousand years ago some crossed the Ice Age land bridge from Siberia to Alaska and then moved southbound to settle in the Americas.
What percentage of irrigated lands are affected by salinization and how does this impact productivity?
Salinization affects at least 20% of all irrigated lands making them less productive through chemical imbalances caused by human activity.