Comets and life 5


Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 5: Summary

It’s in the nature of blogs that developing stories come out backwards. So it may be helpful to summarize the key updates that have arisen.

Comets and life 1 – Recent news: ultra-clean snow melted and sieved for meteoritic particles, at the French-Italian CONCORDIA station in Antarctica, yielded UCAMMs [ultra-carbonaceous Antarctic micrometeorites] with very high carbon contents. Larry Nittler says they “may well have profound implications for the original delivery of organic molecules to the early Earth”.

Comets and life 2 – I did not err in betting heavily in Magic Universe on the magic of polycyclic aromatic hydrocarbons, PAHs. Pascale Ehrenfreund says, “We suggest the aromatic material can be used as a container, as a metabolic unit, and as a genetic information carrier.”

Comets and life 3 – Both Jochen Kissel as instigator and I as reporter remain persuaded that the Kissel-Krueger hypothesis, that chemically active materials from outer space interacted with water to create the first living cells, is still the most promising explanation for the origin of life on the Earth.

Comets and life 4 – I now accept Hoyle & Wickramasinghe’s idea, about pre-existing bacteria in space being rehydrated by the Earth’s water, as another promising hypothesis. And here I repeat what I said at the very end of part 4.

I share Wickramasinghe’s concern about the “cultural barrier”. Science became over-specialized in the creation of university departments in the 19th Century. Since then, in several major advances, earth scientists and biologists offered strong and prolonged resistance when astronomers and astronomically-minded folk said:

  • extinctions due to impacting comets and asteroids have redirected the course of evolution (Halley, about a comet)
  • the Earth’s wobbly orbit around the Sun sets the timing of coolings and warmings in the ice ages (Milankovitch)
  • to explain the origin of life on Earth we have to consider possible cosmic sources (Arrhenius)
  • to understand climate change we have to look to the role of cosmic rays in cloud formation (Svensmark)

Plus ça change, plus c’est la même chose.

You can see all parts of the story (in reverse order) just by clicking on 1c) Comets in the Categories menu.

Or individually:

Part 1

Part 2

Part 3

Part 4

Comets and life 3


Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 3 Initiating biochemical action

Pascale Ehrenfreund rides again (as in Part 2) in the story in Magic Universe called “Life’s origin: will the answer to the riddle come from outer space?”. But please focus first on Wlodzimierz Lugowsky.

I can trace my ancestry back to a protoplasmal primordial atomic globule,’ boasts Pooh-Bah in The Mikado. When Gilbert and Sullivan wrote their comic opera in 1885 they were au courant with science as well as snobbery. A century later, molecular biologists had traced the genetic mutations, and constructed a single family tree for all the world’s organisms that stretched back 4 billion years ago, to when life on Earth probably began. But they were scarcely wiser than Pooh-Bah about the precise nature of the primordial protoplasm.

In 1995 Wlodzimierz Lugowsky of Poland’s Institute of Philosophy and Sociology wrote about ‘the philosophical foundations of protobiology’. He listed nearly 150 scenarios then on offer for the origin of life and, with a possible single exception to be mentioned later, he judged none of them to be satisfactory. Here is one of the top conundrums for 21st Century science. The origin of life ranks with the question of what initiated the Big Bang, as an embarrassing lacuna in the attempt by scientists to explain our existence in the cosmos.

After discussing possible “home cooking” of life by hypercycles, RNA catalysis or lipid catalysis, and touching on the possibility of false starts, the tale turns back to the sky in pursuit of the only hypothesis acceptable to Lugowsky.

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Comets and life 2


Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 2: Cosmic carbon compounds

An earlier post, Part 1 under this heading, commented enthusiastically but briefly on a French team’s find of extraterrestrial dust grains rich in carbon in the snow of Antarctica.

I promised more to come, and here it begins. Part 2 deals with cosmic carbon compounds. Later, Part 3 will reconsider the initiation of biochemical action, and Part 4 will look at suggestions of natural life footloose in space.

There were far more comets around when the Solar System was young, in the “heavy bombardment” phase of Earth history lasting until 3.8 billion years ago. Water is abundant in interstellar space and available to build the icy nuclei of comets. Comets may have delivered most of the Earth’s surface water, essential for life.

Carbon compounds are the other main ingredient for life. Comets’ tails consist mainly of small dust grains released from the nuclei, including grains laden with carbon compounds that may have contributed to the origin of life on the Earth. Here’s a general impression of important “prebiotic” molecules made in the vicinity of dying stars and newborn stars and available for incorporation into comets.

PAHs, polyaromatic hydrocarbons observable in interstellar space, could be ancestral to the aromatic compounds that have the very smell of life. Illustration from Pascale Ehrenfreund & Steven Charnley, 2000 – see reference. Graphic art: ©2000 R. Ruiterkamp

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