Notes for A1.1.7 Extraplanetary origin of water on Earth and reasons for its retention (HL only) - IB | RevisionDojo
A1.1.7 Extraplanetary origin of water on Earth and reasons for its retention (HL only) Notes
Origins of Water on Earth
During Earth's formation, temperatures were extremely high.
Any water present would have evaporated and been lost to space.
Therefore, water had to come from an extraplanetary source, beyond Earth itself.
Tip
Earth holds approximately 1.4 billion cubic kilometers of water, with 98.3% in a liquid state.
The rest exists as solid ice, snow, or water vapor in the atmosphere.
The Asteroid Hypothesis
The most widely accepted explanation is that water was delivered by asteroid collisions.
During Earth's early history, there was a period of intense asteroid bombardment.
Many of these asteroids contained water (as ice or hydrated minerals).
When asteroids collided with Earth, they delivered water to the planet's surface.
Evidence:
Traces of water have been found in material from asteroids.
The isotopic composition of water in some asteroids matches Earth's water.
Modern vs. ancient asteroids:
Ancient asteroids (during Earth's formation) likely contained much more water.
Modern asteroids have lost most of their water due to:
Heat from the Sun evaporating water.
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Questions
Recap questions
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Question 1
Recap question
A planet identical to Earth in mass and magnetic field strength orbits its star at half Earth’s orbital distance, so it receives four times the stellar flux (since F∝r−2). What is the most likely consequence for its surface water over billions of years?
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Note
Exoplanetary origin of water on Earth
The exoplanetary origin of water refers to the theory that much of Earth's water came from sources beyond our planet.
This challenges the older view that all water originated from within Earth itself.
Scientists believe that water was delivered to Earth through various celestial bodies during its formation.
AnalogyThink of Earth as a sponge that absorbed water from passing wet towels (comets and asteroids) during its early years.
DefinitionExoplanetary OriginThe theory that Earth's water came from sources outside our planet, such as comets and asteroids.
ExampleSome meteorites found on Earth contain water-bearing minerals, supporting the idea of an exoplanetary origin of water.
