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Calendar Time
Stephen Greb and Brandon Nutall, Kentucky Geological Survey
The following are calculated dates for Calendar Time
Calendar Time (non-leap year) vs. Geologic Time
| Calendar Time | Geologic Time | |
| Decimal Day | Date:Time | (by=billion years, my=million years) |
| 0 | 0:00 New Years Eve | Beginning of the Earth, Hadeon time (beginning Precambrian time ); 4.6 by |
| 53.48 | March 5, 11:37 am | Archeon Eon , oldest age-dated rocks; 3.8 by |
| 87.28 | March 29, 6:43 am | Oldest fossils, cyanobacteria; 3.5 by |
| 226.14 | Aug. 15, 3:22 am | Oldest fossil cells with a nucleus (eukaryotes); 1.75 by |
| 245.98 | Sept. 3, 11:31 pm | Oldest fossil multi-celled (metazoan) organisms, algae; 1.5 by |
| 321.99 | Nov. 18, 11:.46 pm | Phanerozoic Eon, Paleozoic Era, Cambrian Period ; 542 my |
| 322.95 | Nov. 19, 10:48 pm | Oldest fossil vertebrates, fossil fish; 530 my |
| 326.28 | Nov. 23, 6: 43 am | Ordovician Period ; 488 my |
| 329.85 | Nov. 26, 8: 24 pm | Silurian Period ; 443 my |
| 331.04 | Nov. 28, 9: 36 am | Oldest fossil evidence of vascular land plants, Cooksonia; 428 my |
| 331.04 | Nov. 28, 9: 36 am | Oldest fossil evidence of land animals, a millipede ; 428 my |
| 331.99 | Nov. 28, 11:46 pm | Devonian Period ; 416 my |
| 334.85 | Dec. 1, 8: 24 pm | Oldest fossil large trees ; 380 my |
| 335.24 | Dec. 2, 5: 46 am | Oldest fossil amphibian, Acanthostega ; 375 my |
| 336.51 | Dec. 3, 12:14 pm | Mississippian (early Carboniferous) Period ; 359 my |
| 339.61 | Dec. 6, 2:38 pm | Pennsylvanian (late Carboniferous) Period ; 320 my |
| 339.61 | Dec. 6, 2:38 pm | Oldest fossil evidence of reptiles, Hylonomus; 320 my |
| 341.28 | Dec. 8, 6:43 am | Permian Period ; 299 my |
| 345.08 | Dec. 12, 1:55 am | Mesozoic Era, Triassic Period ; 251 my |
| 346.91 | Dec. 13, 9:50 pm | Oldest dinosaur fossil, Eoraptor ; 228 my |
| 349.21 | Dec. 16, 5:02 am | Jurassic Period; 199 my |
| 352.70 | Dec. 19, 4:48 pm | Oldest fossil bird, Archeopteryx ; 155 my |
| 353.46 | Dec. 20, 11:02 am | Cretaceous Period ; 145.5 my |
| 353.73 | Dec. 20, 5:31 pm | Oldest flowering plants (angiosperms), Archaefructus; 142 my |
| 359.05 | Dec. 26, 1:12 am | Tyrannosaurus rex ; 75 my |
| 359.80 | Dec. 26, 7:12 pm | Dinosaur mass extinction; 65.5 my |
| 359.80 | Dec. 26, 7:12 pm | Cenozoic Era, Tertiary Period ; 65.5 my |
| 364.683 | Dec. 31, 4:24 pm | Oldest hominid fossil, Australopithecus ; 4 my |
| 364.856 | Dec. 31, 8:33 pm | Quaternary Period, Pleistocene Epoch; 1.81 my |
| 364.921 | Dec. 31, 10:06 pm | First of several Pleistocene Ice Ages; 1 my |
| 364.960 | Dec. 31, 11:02 pm | Neandertal man, Homo sapiens neandertalis; 0.5 my |
| 364.993 | Dec. 31, 11:50 pm | Cro-Magnon (modern) man, Homo sapiens sapiens; 0.09 my |
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