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Devonian
Devonian
The Devonian period is a part of the Paleozoic Era and the phanerozoic eon. This period occurred around 360-408 Million years ago. This period of time marks quite a few changes to life on land and these changes also affected life in the ocean as well. during this time, there were two main types of fish, "agnathans" (jawless fish) and "placoderms" (first jawed fish). This period also had some large fish like the Dunkleosteus (shown in the picture) as well as marked the appearance of sharks and lobed-finned fish (ancestors of the ray-finned fish).
This period also had some action on land, although plants were around before this time, they were very small and had no seeds or roots. During this time, plants developed, seeds, roots, and woody tissue allowing for the first forests to arise. Insects and spiders followed shortly and early tetrapods (ancestors of land-dwelling vertebrates) appeared.
This period ended with a mass extinction where around 22% of all marine families disappeared. This is possibly due to the new forest land changing the atmosphere and releasing an overabundance of nutrients into the water.
Silurian
This period is a part of the Paleozoic era and the phanerozoic eon. this period occurred about 408-438 million years ago. this period had a huge climate impact. during this period the earths atmosphere gained enough oxygen from the plants that it formed an Ozone layer concentration. This ozone layer allowed for the climate to stabilize. This ozone layer protected life on land against lethal ultraviolet radiation. life in the ocean was also changing during this time period, there was a wide and rapid spread of jawless fish that emerged, the first jawed fish also appeared, as well as, the first freshwater fish. The jawed fish of this time where larger, had scales, lots of sharp teeth, and spiny fins.
Ordovician
This period is a part of the Paleozoic era and the phanerozoic eon. this period occurred about 438-505 million years ago. This period of time is when the majority of the landmass was a part of the supercontinent gondwana. this is also when gondwana shifted towards the south pole and caused it to break up, most of the land sunk into the ocean. Graptolites,trilobites, brachiopods, and conodonts were the majority of the ocean life as well as, red and green algae, primitive fish, cephalopods, corals, and gastropods. This period was also a time of mass extinction where 60% of all marine invertebrates and 25% of all families went extinct. This is possibly due to the large glaciers that caused sea levels to drop. This period also has rocks that are comprised of some of the oldest vertebrate fossils.
Cambrian
This period is a part of the Paleozoic era and the phanerozoic eon. this period occurred about 505-570 million years ago. This period had quite a bit going on. it is widely known for the numerous hard-shelled fossils that first appeared. During this period, the supercontinent rodinia broke apart. Another feature that this period is probably most known for is the "Cambrian explosion" where there was a huge evolutionary burst of animals dating from 545-525 Million years ago. There was a very rapid proliferation of diversity of living things, most of which are now extinct and only known due to the fossil record. This was when the first animal with a backbone arose. Trilobites (seen in the picture) were a huge part of this period. As the period went on, it got less divers than when if first began.
Precambrian
This section of time includes the eons, Proterozoic, archean, and hadean. this section is about 570-4,550 Million years ago. It is known as the, "Age of early life". This time frame is when the continents formed and our modern atmosphere developed. During this time, early life evolved and flourished. we would start to see soft-bodied animals like worms and jellyfish rome the ocean. the Hadean eon is when the first rocks formed and although there is little that has been preserved from this time we know that this was a time of massive volcanic activity and frequent collisions with astriods occurred. The Archean Eon was when the continental crust started to solidify and form. this formed large landmasses. this is also when the first signs of life appeared in the form of micro mats called, stromatolites (as seen in the picture).
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