Original Water

More than two thirds of Earth's surface is covered by water.

The Asteroid Belt

If Earth's primordial water was boiled off from the intense heat during planetary cooling, where did Earth's abundant water originate?

The origin of Earth’s water remains a mystery.

A prevailing hypothesis is that Earth's water came later from collisions with water-bearing comets or proto-planets from the outer reaches of the Asteroid Belt

Recent analysis of the composition of water sampled on comet 67P suggest Earth's water might not have come from cometary collisions (Life from Comet Collisions).

Scientists suggest that one key to solving the mystery of Earth's abundant water is found in the D/H ratio or the flavor of water. The D/H ratio is the proportion of Deuterium (symbol D) to Hydrogen (symbol H). The ratio of these two hydrogen isotopes might provide clues to the origin of Earth's water.

Deuterium is a form of hydrogen (i.e., hydrogen isotope) that has an additional neutron not present in common hydrogen. There are about 6,420 hydrogen atoms for every deuterium atom found in the world's oceans.

Deuterium can replace hydrogen in water molecules. The properties of D₂O differ from H₂O (common water). D₂O is called heavy water because it's 10.6% denser than H₂O. D₂O is also more viscous than H₂O.

The current opinion that science and poetry are opposed is a delusion. On the contrary science opens up realms of poetry where to the unscientific all is a blank. Those engaged in scientific researches constantly show us that they realize not less vividly, but more vividly, than others, the poetry of their subjects.
― Herbert Spencer, Education, Intellectual, Moral, and Physical (1861)

Analysis of the composition of water sampled on comet 67P, along with previous D/H analysis of other comets show a range of ratios generally containing higher amounts of deuterium than Earth.

Deuterium to Hydrogen Ratio in the Solar System

Source: ESA

Of the deuterium to hydrogen ratios detected in the solar system, the European Space Agency reports:

Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth’s water.

The D/H ratio of water sampled on comet 67P is three times greater than that of Earth's oceans.

Scientists are are turning their attention to asteroids. Meteorites from asteroids in the Asteroid Belt have a closer match to the D/H ratio of water on Earth. Meteorites have a much lower water content than comets. However multiple serious of meteorite bombardments could have produced Earth's oceans.

Water does not resist. Water flows. When you plunge your hand into it, all you feel is a caress. Water is not a solid wall, it will not stop you. But water always goes where it wants to go, and nothing in the end can stand against it. Water is patient. Dripping water wears away a stone.
― Margaret Atwood, The Penelopiad

REFERENCES

• A Comet's Tale, shared on Google Plus by Brian Koberlein, 11 Dec 2014.
• Origin of Water on Earth, Wikipedia.
• Rosetta Fuels Debate on Origin of Earth's Oceans, European Space Agency, 10 December 2014.

Life from Comet Collisions

The biosphere covering Earth remains a deep mystery. Where did life originate?

Bioluminescent dinoflagellates lighting a breaking wave at midnight

Earth might well have coalesced from cosmic dust and gas. Billions of years later, a thin raft surrounding Earth teems with co-dependent organisms.

The question of the origin of life is essentially speculative. We have to construct, by straightforward thinking on the basis of very few factual observations, a plausible and self-consistent picture of a process which must have occurred before any of the forms which are known to us in the fossil record could have existed.
— John Desmond Bernal

Where did the ingredients for the simplest unicellular life forms come from? Life's ingredients might have come from comets.

Early Earth was not very hospitable when it came to jump-starting life. In fact, new research shows that life on Earth may have come from out of this world.
― Astrobiology Magazine

Comet Hale Bopp

Comets are vestiges from the formation of our solar system some 4.5 billion years ago. Comets that move into range of space travel, arrive well-preserved from the freeze locker of the outer solar system.

As it travels near the Sun and Earth, a disintegrating comet represents a treasure-trove of hard data about conditions present during the early stages of the solar system.

The composition of comets interests us because scientists posit that life-building organic compounds might have come from icy comets that collided with Earth millions of years ago.

Organic compounds form the basis of proteins and nucleobases (the building blocks of DNA and RNA). Oceans might have been formed from icy comets and asteroids crashing into Earth.

The first comet landing of a robotic spacecraft touched down on Comet 67P on November 12, 2014. Until then, our knowledge of comets came from a handful of flyby space missions

Comet 67P

Comet 67P

The robotic lander Philae bounced to rest on Comet 67P more than 10 years after being launched from Earth by the European Space Agency.

The Philae landing was a historical touchdown on a comet nucleus.

Philae transmitted in-situ data that will enable scientists to determine the composition of the comet's surface material.

Our Quest

Comets were once believed to be harbingers of human destruction by anthropomorphic gods. Our understanding of our habitat and origin accrues through scientific discovery.

Scientific discovery yields physical explanations to mysterious and once feared phenomena. Our appreciation of the far-fetched phenomena of life grows with every scientific revelation.

Our quest to solve the existential puzzle continues.

The origin of life is a complex narrative of improbable events. The lineage of events stretch back perhaps 13.8 billion years to the Big Bang or beyond.


REFERENCES

• How Did Water Come to Earth? Brian Greene, Smithsonian Magazine, May 2013.
• Mission to Land on a Comet, NASA Science News, 31 January 2012.
• The Shocking Source for Life's Origin, Astrobiology Magazine, 27 August 2013.

Grounded

Humans are grounded. Most of us will never experience weightlessness, yet gravity is a force that covertly acts upon our sense of reality.

Gravity is ruled by mass. As mass goes, so goes gravity. Earth's mass is heterogeneous and unevenly distributed. Contrary to the notion of a static terra firma, the distribution of mass changes over time.

Gravity Recovery and Climate Experiment visualizations of the Earth show variations in Earth's gravitational field. Color zones (right) indicate gravity anomalies where gravity is stronger or weaker than it would be if Earth was a perfectly smooth sphere with homogeneously distributed mass.

The continental spine of the Andes represents an aggregation of mass and a corresponding but imperceptibly stronger gravitational pull indicated by the deep red-colored zone along the coast of South America.

Large earthquakes deform Earth's crust creating local variations in gravity.

The blue zone in the image below shows a weaker gravity deviation, or gravity scar, near the 9.0 magnitude earthquake that struck in the Pacific Ocean east of Honshu Island in March 2011.

Gravity scar following Honshu earthquake

It must have appeared almost as improbable to the earlier geologists, that the laws of earthquakes should one day throw light on the origin of mountains, as it must to the first astronomers, that the fall of an apple should assist in explaining the motions of the moon.
― Charles Lyell, Principles of Geology, Volume 3, 1833.

REFERENCES

• Earth's Gravity Scarred by Earthquake, ESA. 3 December 2013.
• Gravity Recovery and Climate Experiment (GRACE).
• Principles of Geology, Volume 3, Charles Lyell, 1833, London.