 Evolution of life in the Ocean and Classification of the Marine Environment

Evolution of Life in the Ocean  Life on Earth began in the oceans.  Oxygen in the ocean came from algae and plankton. Oxygen in the atmosphere wasn’t high enough for life to exist on land.  Life existed only in the oceans for over 4 billion years of Earth’s 4.6 Billion year history.  For most of the nearly 4 billion years that life has existed on Earth, evolution produced little beyond bacteria, plankton, and multi-celled algae.  First land plants didn’t exist until 470 million years ago and first land vertebrates didn’t exist until 380 million years ago.

Stromatolites  Stromatolites are algal mats that grow in mounds in the ocean.  Today, stromatolites in Shark Bay, Australia are some of the only living examples.  Been around since Cambrian over 500 million years ago.  Provide evidence of how oxygen was put into early Earth’s ocean and atmosphere.

Oxygen is key to life  As oxygen increased, larger and more complicated life can exist.  After algae, the Ediacaran period about 600 million years ago, is the first evidence of multicelluar organisms.  Scientists still have trouble classifying and identifying these unique organisms.

Cambrian Explosion  About 540 million years ago, life in the ocean exploded in diversity.  Called Cambrian Explosion.  Likely due to increase in oceanic and atmospheric oxygen.  All known animal lineages of the present can be traced to this time period.  Animals include: Fishes, Trilobites, Mollusks, Echinoderms, and Brachiopods.  Plants include: Sponges, corals, stromatolites

Ordovician Oceans  Great Ordovician Biodiversification Event  Genera increased exponentially in just 25 million years.  Nautiloids, Cephalopods (squids) first appeared. Also Horseshoe Crabs!  First Jawed fish appeared near end of Ordovician.  A major mass extinction occurred at the end of this period and about 50% of ocean genera went extinct!

Devonian Oceans  Age of fishes!  Firs amphibians appeared making transition from ocean to land.  Armored Placoderm (went extinct at end of Devonian)  Jawless fish declined.  Bony fish diversified.  First sharks appeared.  Mass extinction at end of Devonian.

Carboniferous Oceans  Sharks and bony fishes diversified.  Foraminifera also were abundant  Trilobites are on the decline.