What Evidence Do We Have for the Late Heavy Bombardment Period?

Updated on September 23, 2018
1701TheOriginal profile image

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.


The Conventional Theory And Clues For It

When the solar system formed, it was a swirling disc full of debris that slowly grew into planetesimals, or what we can consider to be planet building blocks. About 4.6 billion years ago, those components began to glob together and form the planets, with one in particular called Theia impacting with us and eventually forming the moon. As the years rolled by, the number of planetesimals dwindled until none were left as they either merged together or were destroyed through impacts. Thus, even hits from objects in space started to dwindle as well. The LHBP is frequently seen as the last major upheaval in the solar system before everything settled down (more or less) after this settling down (Kruesi “When” 32).

The conventional idea is that the LHBP occurred 4.1 to 3.8 billion years ago. Much of the evidence for this comes from our celestial neighbor the moon. Why? Because its surface is like a cassette recorder. Anything that happens to it is preserved on its surface, while Earth has plate tectonics and erosion wiping away evidence of past events. By looking at the craters on the moon we can get an idea of the size and angle of impact. Looking at argon-40/argon-39 radioactive levels from moon rocks brought back by Apollo missions in the areas around the impacts, it indicated the time frame mentioned above, placing the LHBP as a post-lunar formation event. At the time of this conclusion, in 1974, the idea of the LHBP was not popular. Scientists argued that the team behind the study (Fouad Tera, Dimitri Papanastassiou, and Gerald Wasserberg) did not collect a diverse enough sample size to draw accurate conclusions. After all, what if their rocks all came from just one event? Lunar rocks brought back by Apollo astronauts come from areas of the moon that total just 4% of the total surface area, hardly a fair sampling. It was later shown that new impactors and lunar magnetism could also skew the argon readings, making them an unreliable dating gauge. More rocks from different areas would lead to better results. And after looking at known moon rocks that have fallen to Earth, they are all in the required timeframe for the LHBP and relatively agree with each other (Kruesi “When” 32-3, Packham).

As for the actual object that is colliding to form the crater, it is vaporized upon impact because of the energies involved. The vapor that results does condense into what we call sphericules, which fall back to the surface much like precipitation. They are usually in the millimeter to centimeter size range and can tell us details about the composition and violence of the impactor (Kruesi “A Longer”).

In fact, Earth has layers of sphericule that have become trapped in rock layers. Using geological dating techniques, we have found that the 14 known boundary layers have different subgroups. 4 of them are from 3.47-3.24 billion years ago, 7 are from 2.63-2.46 billion years ago, 1 is from 1.85 billion years ago, and 2 are rather recent, with one of them being the KT boundary aka the event that wiped out the dinosaurs (Kruesi “A Longer”).

The moon itself shows evidence all over its beaten surface for the LHBP. Surface studies show that the crust is fragmented - heavily - to the point that it allowed for an easier flow of magma to fill in certain craters that we see today. Gravity readings from the GRAIL probe showed this fracturing after surface anomalies were subtracted from the data and the trends of the patterns mime that of surface impacts seen. The grouping had to be close on a timescale to bring about the effects seen, hinting at a period of heavy bombardment (MIT).


Mainstream Ideas Overturned

It was during an analysis of these boundaries that Jay Melosh and Brandon Johnson (both from Purdue University) found some new clues that may revise out ideas behind the LHBP. In an April 25, 2012 issue of Science, they found that based on the size of other boundary layers, the LHBP likely caused the 1.85 billion-year boundary layer. They determined this by comparing the sphericules and noted that those from this layer resulted from massive impacts. This places the LHBP way later than previously thought (Ibid).

But it gets even better, folks. A separate study by William Bottke (from the Southwest Research institute in Boulder, Colorado) looked into why the LHBP was so long in the first place. When looking at the likely impactors, they seem to originate from a zone in the inner asteroid belt which no longer exists. According to the Nice Model, this is because an orbital shift between Uranus and Neptune caused objects to be thrown about. Using this model, it not only caused outer solar system objects to be thrown in but also inner ones as well, accounting for the missing impactors and also giving the LHBP a longer timeframe (Kruesi “A Longer,” Kruesi “When” 33, Choi).

Works Cited

Choi, Charles Q. “Asteroids Battered Young Earth Longer Than Thought.” Space.com. Purch, 25 Apr. 2012. Web. 16 Nov. 2016.

Kruesi, Liz. “A Longer Late Heavy Bombardment?” Astronomy Aug. 2012. Print.

---. “When Earth Felt Cosmic Rain.” Astronomy Nov. 2012: 32-3. Print.”

MIT. "Study finds barrage of small asteroids shattered Moon's upper crust." Astronomy.com. Kalmbach Publishing Co., 14 Sept. 2015. Web. 04 Sept. 2018.

Packham, Christopher. “Researchers Question Apollo-Era Evidence for the Late Heavy Bombardment.” Phys.org. ScienceX Network, 04 Oct. 2016. Web. 14 Nov. 2016.

© 2017 Leonard Kelley


    0 of 8192 characters used
    Post Comment

    No comments yet.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, owlcation.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://maven.io/company/pages/privacy

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)