Important dates in Earth history

(with reference to Kentucky)

(ages are in million years before the present)

Precambrian Era

• 4600 Beginning of the Earth (Students can draw the Earth. Between 4600 and 3900 students can draw volcanoes and rain clouds to symbolize formation of the Earth's crust, atmosphere, and oceans).
• 3900 Inferred origin of life (first cells)
• 3800 Oldest age-dated rocks on the present surface of the Earth
• 3600 Fossil evidence of blue-green algae and stromatolites. These dominate the world for the next 3 billion years.
• 3250 First fossil evidence of bacteria.
• 1400 First fossil evidence of single-celled life with a cell nucleus.
• 1500 First multi-celled organisms (Draw seaweed and algae).
• 670 Oldest fossil evidence of marine worms and jellyfish.

Paleozoic Era

570 Cambrian Period

• 570 Abundant fossil evidence of invertebrate life throughout the world. Brachiopods, corals, snails, and trilobites were common. *Kentucky was mostly covered by shallow seas and probably looked much like the Bahamas today (without the palm trees, sea gulls, and fish!)
• 515 Burgess Shale organisms (Canada). Famous fossil locality in which soft parts of marine invertebrate organisms were preserved. Most notable may be the first animal with a notochord (i.e., a flexible rod that provides a supporting structure in an animals body) , Pikaia, a pre-vertebrate animals that may be the ancestor of all animals with backbones.

505 Ordovician Period

• 505 First fish (the first fish, called Agnathids, were jawless)
• 470 First fossil evidence of land plants. The first plants looked like lichen. These probably did not reach Kentucky for some time, since Kentucky was mostly covered by shallow seas during the Ordovician.
• 470 *Approximate age of the oldest rocks exposed at the surface in Kentucky (see geologic map). These rocks are composed of limestone and contain abundant brachiopods, bryozoans, cephalopods, trilobites, and gastropods; all indicating that Kentucky was covered by shallow seas.

438 Silurian Period

• 438 *Silurian rocks were partly eroded in Kentucky, prior to deposition of Devonian rocks so that Kentucky is thought to have been land during at least part of the Silurian.
• 430 First vascular land plants were present. These primitive plants had no leaves.
• 414 Oldest fossil evidence of lung fish (i.e., fish with the capability of breathing air)

408 Devonian Period

• 408 Oldest fossil evidence of mosses (Land plants are starting to diversify).
• 400 *Approximate age of the fossil beds exposed at the Falls of the Ohio in Louisville, Ky. Coral fossils are common, especially horn corals. Many animals lived among the corals including bony fish called arthrodires. These are the oldest fish fossils in Kentucky.
• 385 First insects (beetles), scorpions, and centipedes.
• 380 First lobe-finned fish. These fins were an important adaptation, that would ultimately let fish walk on land.
• 375 First amphibians, the oldest evidence of land vertebrates.
• 370 First sharks. *In Kentucky, deeper seas covered the State. Thick, black shales accumulated in the seas, which later became the source for most of the oil and natural gas we produce today. Sharks and bony fish called arthrodires were common in these Devonian seas.
• 375 *Age uncertain, but close to the oldest plant fossils from Kentucky, wood and bark of trees indicates that the sea level had dropped and parts of Kentucky were dry land and colonized by trees.
• 365 First seed plants (gymnosperms). These looked like ferns.

360 Mississippian Period

• 360 *In Kentucky, shallow seas once again covered most of the State. Crinoids and colonial corals are common fossils. Starfish also occur. Toward the end of the Mississippian, the seas withdrew and Kentucky was a coastal area.
• 330 First possible evidence of fossil reptiles. Also, oldest fossil evidence of conifers, seed-bearing plants with cones.
• 330 *Oldest fossil land vertebrate in Kentucky, a 5 foot long amphibian.

320 Pennsylvanian Period

• 320 *Kentucky continued to occupy a coastal position during most of the Pennsylvanian. Broad swamps were common, somewhat similar to the Everglades today. Common fossils include plant fossils like ferns. This is when Kentucky's coal was formed.
• 315 *Reptile trackway from McCreary County. Fossil footprints and tail drag mark of a small lizard were once the oldest evidence of reptiles in the world!
• 312 *Volcanic ash fall covers parts of the swamps in Kentucky.

286 Permian Period

• 286 *Permian rocks are mostly missing from Kentucky. Preservation of Permian strata in nearby states indicates that Kentucky was mostly land, and that dry, desert-like conditions may have occurred.
• 260 Sail-backed reptiles like Dimetrodon and Edaphosaurus are characteristic.
• 245 The Great Paleozoic Extinction. The greatest mass extinction of all time. Ninety-six percent of all life on Earth perishes. Draw a tombstone here!
• This is also the a time when all of the continents in the world had collided to form one great supercontinent, called Pangea.

245 Mesozoic Era "Age of Reptiles"

Triassic Period

• 245 *Triassic rocks are missing from Kentucky, but information from nearby states suggests that Kentucky was probably land during the Triassic.
• 240 First crocodiles.
• 228 First dinosaurs (about the size of a cat) Eoraptor, Fabrosaurus, Lesothosaurus, and Saltoposuchus are examples of early dinosaurs
• 221 First mammals (looked like shrews)
• 216 Dinosaurs begin to diversify. Coelophysis, and Plateosaurus are examples of late Triassic dinosaurs.
• 210 First turtles.

208 Jurassic Period

• 208 *Jurassic rocks are missing from Kentucky, but information from nearby states suggests that Kentucky was probably land during the Jurassic.
• 195 Dilophosaurus is a good example of an early Jurassic dinosaur.
• 155 First bird, Archeopteryx.
• 152 Apatosaurus, Brachiosaurus, and Diplodocus are good examples of late Jurassic long-necked dinosaurs.
• 150 Allosaurus and Centrosaurus are good examples of late Jurassic meat-eating dinosaurs.
• 148 Kentrosaurus and Stegosaurus are good examples of late Jurassic plate-backed dinosaurs.

144 Cretaceous Period

• 144 *Cretaceous sediments are preserved in the Jackson Purchase area of western Kentucky, and indicate that Kentucky was mostly land during the Cretaceous. No dinosaur fossils have been found in Kentucky, but they may have lived here.
• 115 First flowering plants (angiosperms). Magnolias are a good example.
• 82 Duck-billed dinosaurs were common like Corythyosaurus, Edmontosaurus, Lambeosaurus, Maiasaurus, and Parasaurolophus. Maiasaurs are examples of dinosaurs from which fossil nests, eggs, and baby dinosaurs have been found.
• 80 Protoceratops was the first dinosaur from which fossil eggs were discovered.
• 75 Ceratopsian (shield-headed) dinosaurs were common in the late Cretaceous. Examples are Monoclonius, Styrakosaurus, and Triceratops.
• 70 Some of the most popular meat-eating dinosaurs were common in the late Cretaceous. Examples are raptors such as Velociraptor, and the largest meat-eating dinosaur of all time, Tyrannosaurus rex (both in the Jurassic Park movie)
• 65 Extinction. Comet or meteor collides with the Earth and all animals on land and sea weighing more than 3 kg perish. Draw a big explosion or another tombstone.

65 Cenozoic Era "Age of Mammals"

Tertiary (Paleogene and Neogene Periods)

• 65 *Tertiary sediments are only preserved in a small area around Kentucky Lake in western Kentucky. Most of Kentucky appears to have been land during the Tertiary, and probably looked much as it does today.
• 64 First ancestors of dogs and cats.
• 60 Grasses become widespread for the first time.
• 57 First ancestors of pigs and deers.
• 55 First horses (the first horses were tiny, about as big as a dog).
• 45 First ancestors of rabbits.
• 39 First monkeys.

1.6 Quaternary Period

• 1.0 *First of four ice ages. Thick, glacial ice sheets head south from Canada to just north of Kentucky. Draw a snowflake or thermometer!
• 0.7 *Quaternary sediments are preserved in river sediments, caves, and sinkholes thoughout the State. Throughout the Quaternary, Kentucky looked much as it does today, except at times it was much cooler.
• 0.5 Oldest human-ancestor fossil, Homo habilis.
• 0.1 First modern man, Homo sapiens.
• 0.05 *Age uncertain, but close to the time when fossil mammoth and mastodon
• bones were buried at Big Bone Lick, in northern Kentucky.