Comets and Life On Earth

Donald Yeomans
Donald Yeomans

With the recent discovery of the amino acid glycine in the comet dust samples returned to Earth by the Stardust spacecraft, it is becoming a bit more clear how life may have originated on Earth. Water is a well-known ingredient in both comets and living organisms, and now it appears that amino acids are also common to comets and living organisms. Amino acids are used to make proteins, which are chains of amino acids, and proteins are vital in maintaining the cell structures of plants and animals.

Amino acids had previously been identified in meteorite samples, and these samples are thought to be the surviving fragments from asteroid collisions with the Earth. So now it appears that both comets and asteroids in the Earth’s neighborhood, the so-called near-Earth objects, delivered some of the building blocks of life to the early Earth.

Asteroid Eros - Mosaic of Northern Hemisphere
Asteroid Eros - Mosaic of Northern Hemisphere. Image Credit: NASA/JPL/JHUAPL
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Impacts of comets and asteroids with the early Earth likely laid down the veneer of carbon-based molecules and water that allowed life to form. Once life did form, subsequent collisions of these near-Earth objects frustrated the evolution of all but the most adaptable species. The dinosaurs checked out some 65 million years ago because of an impact by a six mile-wide comet or asteroid off the coast of the Yucatan peninsula. Fortunately, the small, furry mammalian creatures at the time were far more adaptable and survived this impact event. Thus, present day mammals like us may owe our origin and current position atop Earth’s food chain to these near-Earth objects, one of which took out our dinosaur competitors some 65 million years ago.

Today, most of the attention directed toward near-Earth objects has to do with the potential future threat they can pose to life on Earth. However, the recent Stardust discovery of a cometary amino acid reminds us that, were it not for past impacts by these objects, the Earth may not have received the necessary building blocks of life, and humans may not have evolved to our current preeminent position on Earth. While giving thanks to these near-Earth objects, we still need to make sure we find the potentially hazardous comets and asteroids early enough so we don’t go the way of the dinosaurs.

For more information on near-Earth objects, see:

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    8 Responses to “Comets and Life On Earth”

  1. Paul Höfer Says:
    August 17th, 2009 at 9:33 pm

    It may be that comets and asteroids delivered amino acids to earth also at the beginning but Miller experiments showed amino acids (at least the most simple forms like glycine) should had been produced on earth itself by “simple” chemistry. So the creation of life on earth was not essentially dependant on the support of molecules like glycine being delivered by comets or asteroids. I think one should keep this in mind.

  2. Ed Daniels Says:
    August 18th, 2009 at 12:22 pm

    Thank you for that very interesting look at the origin of life on earth. When you think of it, it is true that near earth objects are not just threats but part of the reason that we are here.

  3. Tman In Tennessee Says:
    August 20th, 2009 at 3:13 pm

    Mr. Yeomans,

    Do you think that if NASA was able to be more proactive about pushing the research behind projects like Stardust and Deep Impact that this may help to bridge the funding gap for NASA’s NEO detection and mitigation programs? It seems that not enough people in power take the asteroid issue seriously enough and I wonder if maybe there is a more effective way of publicizing the importance of NEO research by demonstrating the scientific discovery potential of these wayward objects.

    I love the new site by the way, it looks fantastic. Please keep up the great work!

    Don Yeomans says:

    NASA-supported scientists and flight projects, including those dealing with comets and asteroids, play an important role in the exploration of our solar system. Near-Earth Object survey programs also play an important role — and while we can be doing more, NASA is the leader in this field. Perhaps we need to redouble our efforts to make the importance and significance of this research better known to the public. After all, it is the public who pays for this research. The “Asteroidwatch” website (and its widget, RSS and twitter signups) is an attempt to get this word out.

    For more information about Near-Earth Objects, please visit NASA’s “Asteroidwatch” website at:

  4. wan2b Says:
    September 9th, 2009 at 9:46 am

    I am concerned that the economy or the lack of understanding of the work done in space exploration will prevent us from some day having the chance to save ourselves from a serious impact. I know we have plenty of evidence of earth impacts and that is just the ones not erroded away by time. I think there may be some we just haven’t regocnized as impacts aswell.

    Ever notice how surface water drainage on soil with fine sediments from 6 feet up looks just like river beds from 5000 feet up. The pattern of erosion and areas of deposit build-up are the same. Point being that the same physics apply in both small and large scales. Even from high altitudes such as satellite imagery the big picture may be showing us exactly what is there. Well with that in mind take a look at the Taklamakan desert in China, (N 32.86113 E 68.40088), on any satellite image from Google or ACME mapper 2.0 or what ever you like. Does it look like a glancing blow from a comet or asteroid started directly east of the Taklamakan desert basin, finally digging into the Earth’s crust propelling huge amounts of its dust and mineral deposits as far as Bagdad. What might be buried in the large deposits just west of the Himalayas? Is the sand in this desert different from other desert sands, because it was part of the asteroid or comet? Possible the entire impact site and debris field has been slightly distorted by the Himalayan Mountain Range. Or is it possible this impact happened before this range was developed by the tectonic plates pushed up in this area creating the Himalayas? Crazy sure, but sometimes things are really what they appear. Ok start laughing and tearing me apart, but I still pose the question and will learn from any and all sources willing to constructively criticize and educate a beginner. Thanks.

  5. Comets and Life On Earth | Hometown Pasadena Says:
    September 18th, 2009 at 10:03 pm

    [...] the Full Story at JPL [...]

  6. Michael Jordan Shoes Says:
    October 6th, 2009 at 12:22 am

    Good atricle indeed. thanks for sharing

  7. Satalink Says:
    October 15th, 2009 at 3:08 pm

    I take a look at NEO list every now and then. This week there have been two NEO objects come up with little warning that have a caculated distance of less than one lunar distance. In the few years that I have been monitoring the NEO list, it’s not often that we experience an object with a distance of less than 1LD. Am I mistaken in thinking this is unusual?

    Don Yeomans responds:

    Neal, two NEOs passing within 1 lunar distance in the same week is somewhat of a low probability happenstance – but certainly not out of the question.

  8. Says:
    May 5th, 2011 at 2:00 pm

    Blogs jpl nasa.. Keen :)

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