Except that there are evidence that microorganisms from the domain Bacteria and from the domain Archaea, have flourished for 3 billion years prior to the earliest evidence of eukaryotes during the Cryogenian period (720 to 635 million years ago) existed in the sea, were main planktons (of protists, protozoans; various earlier algae), with the protozoans being the most basal form of animals. The Cryogenian was then follow by diversity radiation of more complex marine animals, earliest multicellular animals, the sponges, in the Ediacaran period (635 to 538 million years ago), and then in Cambrian (538 to 485 million years ago).
Through these 3 periods, marine invertebrates flourished in the last 2. There are trace evidence that even as in movements on lands, by some unknown arthropods in the late Cambrian.
The points are there were no plant life on dry land, yet when marine life flourished in these periods. When biologists or paleontologists talk of “flora” in the Ediacaran or in the Cambrian, they are not talking of any land plants, but of algae, like green algae that we commonly see them as seaweed.
Your position on about water, plants and then animals are wrong, inaccurate. There were no plants growing on land, period to Ediacaran sponges, as I said, the earliest multicellular marine animals. Marine arthropods, like the trilobites from middle Cambrian predated the earliest land flora.
The earliest terrestrial plants didnt reproduce by seeds, but by spores. These were more like mosses, non-vascular and spore-reproducing plants, from the Ordovician period. Vascular plants (like ferns) didn’t appear until the Silurian period, but these plants still reproduce by spores, not by seeds.
Seed plants (or spermatophyte), didn’t appear until the Devonian period, the earliest appearance around 319 million years ago...and these earliest didn’t produce flowers nor fruits until the Cretaceous period.
The earliest fishes were jawless fishes, and they have been around as early as the late Cambrian. So land plants actually didn’t predated these jawless fishes.
jawed fishes appeared in the Silurian period, and the earliest fishes with bony skeletal structures around 425 million years (also in Silurian).
The earliest land animals weren’t vertebrates, but were invertebrates like arthropods, like insects, possibly as early as 400 million years ago.
the point is that marine animals actually existed before there were land plants, and no land plants produced seeds until much later.
