You wouldn’t think life on a planet being bombarded by debris in the early days of its solar system would have much chance for survival. Indeed, the prospect of being pummeled for millions of years in the Late Heavy Bombardment has led to scenarios in which life started, was extinguished, and re-started on this planet, the idea being that the massive cratering we see on objects like the moon was also being enacted here. But maybe we can make a virtue of necessity and consider what all those incoming objects might have done long-term to improve the atmospheres of the planets they landed on.
So goes the thinking in a new study that examines the composition of ancient meteorites to see what they would do when heated to temperatures like those caused by a fiery descent to Earth. Using a method called pyrolysis-FTIR, in which the meteorite fragments were quickly heated (at a remarkable 20,000 degrees Celsius per second), the team measured the carbon dioxide and water vapor released. It turns out that the average meteorite would release twelve percent of its mass as water vapor, and another six percent as carbon dioxide after entering the atmosphere.
That doesn’t add up to much from any single meteorite, but the Late Heavy Bombardment (LHB) some four billion years ago wasn’t an average time. The research team used models of meteoritic impact rates during the bombardment to calculate that billions of tons of carbon dioxide and water vapor would have been delivered to Earth’s atmosphere each year over the entire twenty million years that spanned the LHB. The same phenomenon would have occurred on Mars, making both planets warmer and wetter, at least for a time. Mark Sephton (Imperial College, London) and a co-author of the recent paper on this work, comments:
“For a long time, scientists have been trying to understand why Earth is so water rich compared to other planets in our solar system. The LHB may provide a clue. This may have been a pivotal moment in our early history where Earth’s gaseous envelope finally had enough of the right ingredients to nurture life on our planet.”
To be sure, the delivery of water from the outer system to the Earth has been a major issue in studying how planets form and evolve. What this work does is to put some numbers on the delivery of water and carbon dioxide by meteorites. And the comparison between Mars and our own world shows how different the outcomes could be, with Mars’ lack of a magnetic field contributing to the loss of its atmosphere (no protection from the solar wind). One world’s oceans dry up or turn to ice, while another’s become the staging area for complex life. We now speculate on which outcome is more common as we wait for further news from Kepler and CoRoT.
The paper is Court and Sephton, “Meteorite ablation products and their contribution to the atmospheres of terrestrial planets: An experimental study using pyrolysis-FTIR,” Geochemica et Cosmochima Acta Vol. 73, Issue 11 (1 June 2009), pp. 3512-3521 (abstract). More in this Imperial College London news release.
Interesting news item. I do wonder just how different Earth was before and after the LHB.
interesting. im sure the LHB made a substantial impact.
earth gets just enough heat from the sun to have liquid water on most of its surface, and the magnetic field maintains the atmosphere and so on. mars on the other hand probably had water from the LHB, but with weaker gravity and no magnetic field, it slowly reverted to what it is now. venus could have been a world like ours, but its too close to the sun and it had a runaway greenhouse effect. it also has no magnetic field, which resulted in the loss of all its hydrogen to solar wind.. leaving a dense carbon dioxide atmosphere (almost a planet-wide ocean of gas) behind. hydrogen would react with carbon dioxide to create graphite and (most importantly) water.
i went on a bit of a tangent here, but in general, meteorites can have effects on a developing world.. and perhaps terraforming could be made easier by using comets or other stuff from space. and while a magnetic field may not be necessary for life, it would certainly be a great asset.
“im sure the LHB made a substantial impact.”
I like the pun.
July 17, 2009
Ancient Domes Reveal 3.45-billion-year-old Life History
Written by Anne Minard
Rare, paleosurface view of how conical stromatolites would appear if one snorkeled in the shallows of a reef. Credit: Abigail Allwood
Ancient, dome-like rock structures contain clues that life was active on Earth 3.45 billion years ago, according to new research — and the findings could help shed light on life’s history on Earth and other planets, including Mars.
Abigail Allwood, who studies planetary habitability at NASA’s Jet Propulsion Laboratory, led the research. She and her colleagues studied stromatolites, which are dome- or column-like sedimentary rock structures formed in shallow water, layer by layer, over long periods of geologic time.
Geologists have long known that the large majority of the relatively young stromatolites they study—those half a billion years old or so—have a biological origin; they’re formed with the help of layers of microbes that grow in a thin film on the seafloor.
The microbes’ surface is coated in a mucilaginous substance to which sediment particles rolling past get stuck.
“It has a strong flypaper effect,” said John Grotzinger, a Caltech geologist and a study co-author. In addition, the microbes sprout a tangle of filaments that almost seem to grab the particles as they move along. “The end result,” Grotzinger explains, “is that wherever the mat is, sediment gets trapped.”
So in a young stromalite, dark bands like those seen in the close-up cross section at left indicate organic material. But 3.45 billion years ago, in the early Archean period of geologic history, things weren’t quite so simple.
“Because stromatolites from this period of time have been around longer, more geologic processing has happened,” Grotzinger says. Pushed deeper toward the center of Earth as time went by, these stromatolites were exposed to increasing, unrelenting heat. This is a problem when it comes to examining the stromatolites’ potential biological beginnings, he explains, because heat degrades organic matter. “The hydrocarbons are driven off,” he says. “What’s left behind is a residue of nothing but carbon.”
As such, geologists debate whether or not the carbon found in these ancient rocks is diagnostic of life.
Allwood and her team turned to the texture and morphology of the rocks themselves, from samples gathered in Western Australia. The samples, says Grotzinger, were “incredibly well preserved.” Dark lines of what was potentially organic matter were “clearly associated with the lamination, just like we see in younger rocks. That sort of relationship would be hard to explain without a biological mechanism.”
Full article here:
http://www.universetoday.com/2009/07/17/ancient-domes-reveal-3-45-billion-year-old-life-history/
Origin of Life
Authors: Ashwini Kumar Lal
(Submitted on 21 Jul 2009 (v1), last revised 13 Aug 2009 (this version, v5))
Abstract: The evolution of life has been a big enigma despite rapid advancements in the fields of astrobiology, astrophysics, and genetics in recent years. The answer to this puzzle has been as mindboggling as the riddle relating to evolution of Universe itself.
Despite the fact that panspermia has gained considerable support as a viable explanation for origin of life on the Earth and elsewhere in the Universe, the issue however, remains far from a tangible solution.
This paper examines the various prevailing hypotheses regarding origin of life like abiogenesis, RNA(ribonucleic acid) world, iron-sulphur world, and panspermia; and concludes that delivery of life-bearing organic molecules by the comets and meteorites in the early epoch of the Earth alone possibly was not responsible for kick-starting the process of evolution of life on our planet.
Comments: 27 pages,7 figures (invited review article)
Subjects: General Physics (physics.gen-ph); Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: Astrophysics & Space Science (2008) 317: 267-278
DOI: 10.1007/s10509-008-9876-6
Cite as: arXiv:0907.3552v5 [physics.gen-ph]
Submission history
From: Lal Ashwini Kumar [view email]
[v1] Tue, 21 Jul 2009 06:39:41 GMT (1110kb)
[v2] Fri, 24 Jul 2009 09:13:50 GMT (437kb)
[v3] Sun, 26 Jul 2009 20:50:34 GMT (404kb)
[v4] Mon, 10 Aug 2009 10:38:37 GMT (1100kb)
[v5] Thu, 13 Aug 2009 09:46:52 GMT (525kb)
http://arxiv.org/abs/0907.3552