For this week and some of next, we’ll have some entries that Alexis put together over the summer.

Alexis writes:

Today’s photo is from Wikimedia Commons (also on Flickr) and was taken by Ruth Ellison at Lake Thetis, Australia. Thanks, Ruth!

Today, we start a photo series of prehistoric plants, spanning the Cambrian period to the Cretaceous period, some extant, some long extinct, and some with living relatives.

Dating back to the Early Archaean about 3 billion years ago, stromatolites are evidence of the earliest known photosynthesizing organisms, cyanobacteria. Though cyanobacteria are also known as blue-green algae, they are not related to true algae, which are in the domain Eukaryota and not Bacteria. Modern living stromatolites can be found today in aquatic environments such as Shark Bay, Australia.

Stromatolites are made of alternating layers of cyanobacteria and sediment, and can vary in shape from mounds to pillars. To create these unique formations, the bacteria first weave around sediments to form thin mats. The ideal environment for stromatolite formation is water shallow enough to allow sufficient sunlight for photosynthesis. These can include marine environments, intertidal zones, and lakes like British Columbia’s Pavilion Lake, which is the focus of much research. As more sediment gets stuck to the mats, the cyanobacteria are forced to spread vertically to maintain their access to sunlight. Sediment continues to stick to the organisms and the process continues, building layer on layer, forming a stromatolite.

In the fossil record, stromatolites are identified in cross-section by their curved laminae (via this page on stromatolites). These fossilized sediment layers (the organic bacterial mats having been long decomposed) are the only evidence that remain of the ancient cyanobacteria that we have to thank in part for generating an oxygenated atmosphere.


11 responses to “Stromatolites”

  1. Annie in Texas

    Living rock. Ok, living pre-rock, the rhythm and blues.

  2. Trisha in Texas

    Apologies for the double post (removed double post — Daniel), the computer burped while I was posting. Pleasant Monday to you all, it is heaven here. Walked out the door at 4:45 this morning and it was COOL! After months and months of 100+ degree heat, I almost went into shock. Now if it would just last a few days, mmmmm, I might be able to get outside without melting or turning to ash.

  3. iris lefleur

    My first encounter with this proof of evolution was in upstate New York outside of Saratoga. It is just a pull off on the road side but you can see many formations there. It is claimed that they are from the pre-tectonic plate movements, originally the area was in a tropical environment. If ever you have been to upstate N.Y. you would realize how un-tropical the area is now. I find it quite interesting and think about that when it is below zero temps.

  4. Linda C Miller

    I would never have thought that these were “living” organisms. What a wonderful write up about how it was in the beginning. I would love to see the vertical formations too.

  5. Jim Cornish

    It is great to see a living fossil… not many left if we exclude our politicians! Are these under any kind of threat like the Great Barrier Reef?

  6. Meg Bernstein

    Thanks a million for this series. It’s so hard to find good paleontologically related plant information. I will be pouncing on each one of these the minute the email comes through. Thanks again.

  7. phillip

    ..question…about a fern that is called a ‘DINOSAR’..plant..that can come back to life after being dormant…does it appear to come back to life because its fonds become pliable due to water..or does it actually start to grow..?..

  8. Susan Gustavson

    Fascinating organisms, and what might be what earth life gets taken back down to if we don’t stop doing things like Tar Sands removal the size of Florida.

  9. Erin

    I was so pleased to see stromatolites in the subject line! Thanks; looking forward to this week’s selections . . .

  10. elizabeth a airhart

    do you mean that all five foot seven of me green eyes and big feet
    is sitting here in front of this machine talking to people around
    the world and it all came about because of stromatolites
    well d’ya ever

  11. Bill Barnes

    If those of you happen to frequent fresh water lakes in Florida the same thing can be found but on a much smaller level. The ones in Florida look like the ones pictured here but are brown in color and are about the size of a cantalope cut in half or maybe a large grapefruit cut in half. Breaking one open reveals the numerous layer upon layer of mineralized cells . The ones in Florida are made by iron sulfur purple bacteria . The bacteria extract the sulfur from Iron sulfide and then deposit the iron as a by product.The process also gives rise to the so called sulfur water that is common in shallow wells in Florida . The formation of the stromatolites is also responsible for the vast iron deposits in Michigan and the Great Lakes states from eons ago, presumeably in a much more tropical environment than what is found now. Given a lot of time maybe Florida will be the new iron producing state .
    The fern Phil refers to is Resurrection fern , and its initial response is due to the increase in leaf turgidity by water . It will start to grow afterwards.

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