evo evo

• the earth is about 4.6 billions year old
• thr studying of the age of earth involves looking at fossil records and the theory of evolution
• the geologic time scale is divided into eon, era, periods and epochs
• eras are longer than periods but shorter than eons
• pre cambrian period is 4.6 billions years to 541 million years ago
• 88% of Earth's geologic time scale is the pre cambrian
• pre cambrian- lower levels pf pxygen in the oceans and Atmos
• in precambrian, photosynthetic bacteria created the oxygen rich atmosphere
• the headean eon marks the formations of crust and oceans. some rock fossils like detrical zircon dating revealed associations with magmatic crust cooled down and interactions with water
• the Archaean eon ( 4-2.5 bya) was when earth had cooled down enough for the first signs of life to appear. stromatolites date back 3.7 bya, the oldest identifiable fossil ever recorded
• stable region like gondwanaland via tectonic plates were formed in proterozoic eon (2.5 bya to 541 mya)
• eukaryotic cells appeared in proterozoic eon and by 715 mya, glaciation occured followed by slow warming
• the phanerozoic eon began with the cambrian explosion when pre cambrian biota such as dickinsonia costata went extinct while new groups rapidly arise
• the phanerozoic eon is divided into Paleozoic, mesozoic, and cenozoic
• during the phanerozoic eon, at the latter part of Paleozoic era, all land masses merged as one, called pangea, thatater parted into two, gondwanaland and laurasia
• in Paleozoic era, multicellular organism diversified but it ended with a 90% mass extinction
• mesozoic era was dominated by dinosaurs which became dominant during this time
• the cambrian explosion ( 542 -485 mya) gave rise to major groups of animals
• in cambrian explosion. first arthropods, like the trilobites as well as most marjne phyla like mollusks, invertebrates and echinoderms all prepared in this period
• the first land plants and fungi emerged in ordovician ( 485 - 444 mya )
• bony and jawless fishes arise in silurian (444-419 mya)
• the ordovician-silurian extinction event is the first massive one
• evolution of fishes was at peak at Devonian period ( 419 - 359 mya), such as the lobbed-finned tetrapod fish, tiktaalik on land, insects, fern, trees, seeded plants, and amphibians tribes
• the late devonian mass extinction wiped out 80% of the species in both land and sea
• the carboniferous period (359-252 mya ) has tropical climate. mammalian and reptilian ancestors appeared, while large amphibians ruled the swampy forests
• durin the permian, the supercontinent, pangea was the largest. reptiles diversified , connifers and sypnasids

  ( ancestors of mammals) ruled the continent
• the largest extinction in history occured during the permian period
• the mesozoic era (252 -66 mya ) has triassic , jurassic , and cretaceous periods. dinosaurs dominated then came nectar drinking insects, birds, flowering plants, and mammals
• cretaceous-paleogene (k-pg)extinction wiped out the dinosaurs
• asteroid impact, rising of sea levels, volcanic, and tectonic activities or glaciation are just some theories causing extinction