Fossilized stromatolites a. formed around deep-sea vents. b. resemble structures formed by bacterial communities that are found today in some shallow marine bays. c. provide evidence that plants moved onto land in the company of fungi around 500 million years ago. d. contain the first undisputed fossils of eukaryotes.

Video transcript

Hi all. Welcome back. Our next problem says structures created by photosynthetic cyanobacteria are known as blank fossils. So let's look at our choices here we have choice a trace fossils. Well as we can see by their names these aren't actually remains of an animal but they are things like footprints, trails, burrows left by animals so evidence of them being there. But not actual fossils not actual remains of an organism itself. So but that's not what we're looking for. They're not going to be left by cyanobacteria. So we can eliminate choice. A choice B is a cast fossil and a cast fossil. As you might guess by the name is an impression left when an organism dies in sediment and after the organism the organism decays. That impression is filled in with minerals that harden and you're left with um the outer uh the outer structure of the organism. You can see that by that cast that was formed with the sediment that filled it so we can eliminate Choice B. That is not what we're looking for. Choice C. Says pseudo fossils. And as we might guess by the name, pseudo false or fake. These aren't fossils at all their traces left behind by minerals that mimic evidence of life. And that's because minerals can leave behind highly structured or organized things that look very lifelike. So that's very interesting but it is not left by a cyanobacteria. So let's eliminate choice see so we've just got one choice left. D stromatolites that must be our answer. And indeed stromatolites are layered structures. Okay they're layered structures that are caused by um photosynthetic organisms and they released a sort of adhesive that cement together these layers of sediment. And this is some of these are some of the most ancient fossils on earth, some of them over three billion years old. So our choices D stromatolites as the structures created by photosynthetic cyanobacteria. See you in the next video.