New Ideas on the Origin of Earth’s Water
(Published in The EarthSphere Blog. Cover Image: Let it Flow by WM House; ArcheanArt)
I previously blogged about how water from asteroids and comets set the stage for our biosphere 4.5 Billion years ago. We are the blue planet because of water from space debris captured in Earth’s gravity-well as the planet formed. A recent article in The Conversation added to this discussion by demonstrating a probable connection between solar flares and the formation of water on the outer surface of asteroids. Water created by the sun may keep replenishing the supply of water contained in our solar system’s celestial bodies.
The recent sampling of asteroids by JAXA (the Japan Aerospace Exploration Agency) provided new evidence to complement investigations into the origins of Earth’s water. The gist of these investigations is, water is a common component in the cosmic debris spread across our solar system — i.e., the water came from outer space via asteroids and comets. Asteroids contain a solid core consisting mainly of rocky material and metals, whereas comets are mostly ice, dust, and some rocky material.
Asteroids are further split into three categories:
C-type (chondrite): most common type of asteroid; made of silica rock and carbonaceous materials
S-type (stony): made of silicate materials and nickel-iron
M-type (Metallic): made of nickel-iron only
Despite asteroids having water close in composition to Earth’s water, we face a conundrum since Earth’s water appears to be at the low end of the deuterium to hydrogen (DH) ratio for most cosmic bodies. Many of the common water-bearing C-type asteroids have deuterium-enriched water, making it hard to attribute Earth’s water solely to asteroids. And the water from comets has a much higher DH ratio than Earth’s water.
One of the benefits of scientific research is its methods allow for unexpected results. So, when JAXA granted a group of researchers access to three rare pieces of the Itokawa asteroid, collected in 2010 by JAXA Hayabusa mission, the researchers hoped to investigate space weathering on the outer dust particles of the asteroid. Technology played into their research since the team worked with a new analytical technique called atom probe tomography. This process allows for the analysis of individual atoms and molecules, and determines their position in a 3D matrix.
During their work, they unexpectedly found water. Specifically, they found a layer near the asteroid’s surface that was rich in both hydroxide (OH) and water (H2O). In the true spirit of scientific research, they pondered the evidence for a bit.
The quandary they faced was that all previous research indicated this near-surface layer should be “dry as a bone.” The presence of water indicated the asteroid was receiving new hydrogen atoms from somewhere. The largest and most prolific source of hydrogen in the solar system is the sun. We also know the sun constantly produces coronal mass ejections, sending blasts of protons and electrons hurtling into space at a million miles per hour or faster. This process gives rise to solar winds.
Remember, a hydrogen atom is the simplest of atomic structures with one proton and one electron. We also know some of the protons riding a solar wind can scavenge an electron on their journey, creating hydrogen. The evidence for this phenomenon was provided by NASA’s Imager for Magnetopause to Aurora Global Exploration spacecraft, which carried a Low Energy Neutral Atom (LENA) imager. Measurements confirmed that about one in every ten thousand protons in a solar wind snatches an electron on its journey to Earth, creating hydrogen.
When Did Earth Become a Water Planet?
The findings from the Itokawa asteroid research gave rise to a new theory. Water is continually produced on the surface of asteroids through bombardment by hydrogen-carrying solar winds. Importantly these newly formed water molecules consist of light hydrogen, not deuterium, perhaps explaining why Earth’s water is lighter than would be expected if it came solely from asteroids. But it still doesn’t tell us when Earth’s ocean’s formed.
Geological evidence (Jack Hills zircons) points to liquid water being present about 100 million years after Earth formed (4.4 billion years ago). Also, theoretical analysis of the early solar system indicates water of varying DH ratios was present in the protoplanetary disc during the first million years after the sun formed. So water was available to Earth when it formed, and zircon analysis says standing water was present 100 million years later. The closest we may come to pinpointing the presence of significant liquid water on Earth may be determining when the planet’s surface cooled below boiling point.
Unfortunately, no one was measuring temperatures at the time. Geologists named the first 500 million years of Earth’s history as the Hadean Eon, under the belief it was “hot as hell” during that time. However, thermodynamic calculations indicate Earth’s Crust may have solidified as early as 10 million years after the planet’s formation. In practical terms, water appears to have been on Earth since the planet’s inception. This scenario means life had the chance to get off to a quick start on a planet rich in water and optimally located to keep from either frying in the sun’s heat or freezing the cold. All life needed to do after this was miraculously emerge.
Water From Cosmic Debris Supports Life (by WM House; ArcheanWeb)
Rising Solar Winds (by WM House; ArcheanWeb)
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Asteroids (Source: NASA) — https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/in-depth/
What is the difference between an asteroid and a comet? (Source: Cool Cosmos)
Deuterium-to-Hydrogen Ratio in the Solar System (Source: Rosetta — European Space Agency)
Scientists Say the Sun May Have Kinda Sprayed the Earth With Water(Source: Futurism)
Up to half of Earth’s water may come from solar wind and space dust (by Luke Daly, Martin Lee, Nick Timms, and Phil Bland; The Conversation)
D/H ratios of the inner Solar System (by L.J. Hallis; Philosophical transactions)
A Cool Early Earth (by John W. Valley)