Earth's water didn't arrive by comet or from its birth
In short: Our planet holds an estimated 325 million trillion gallons of water, yet it began as a barren ball of fire. For decades, scientists debated whether this life-sustaining liquid was born with the Earth or delivered later by cosmic travelers like comets. The truth is far more complex.
The journey of water begins 13.8 billion years ago at the Big Bang. While hydrogen formed quickly, oxygen required nuclear fusion in the hearts of massive stars. About 600 million years after the Big Bang, these stars ended in supernova explosions, scattering oxygen and other heavy elements into space. These atoms fused with hydrogen to form water molecules, which froze into ice and mixed with dust particles.
As gravity pulled this matter together, it formed planets, asteroids, and comets. However, evidence suggests Earth did not keep its original supply. A colossal impact with a Mars-sized body called Theia turned the early Earth into molten rock, evaporating most of its water and spewing the rest into space. This left the planet's initial water budget severely depleted.
For years, comets were the primary suspects for delivering our oceans. However, 2012 research revealed that comet water has twice the ratio of deuterium to protium isotopes compared to Earth's water. Furthermore, analysis of lunar rocks by Lawrence Livermore National Laboratory (LLNL) scientists suggests a different origin. By measuring rubidium-87 and strontium-87 isotopes, researchers found that the bodies forming the Earth-moon system were likely dry from the start.
This leaves a significant mystery: if comets are chemically distinct and our early precursors were dry, we must still be uncovering the specific mechanisms of how our planet became so wet. We know it sits in the 'Goldilocks zone'—the perfect distance from the Sun to maintain liquid water—but the exact delivery system remains one of science's most enduring questions.
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Sources
- Summary by Intellect · source: How did water get on earth? Where does water come from?
- Also: Where on Earth did the water come from?
- Also: www.scientificamerican.com — How Did Water Get on Earth?
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