The Way of Science

UNIT 4

APPENDICES

APPENDIX #2: A Brief Timetable for the Universe

13-14,000,000,000 years ago
(13-14 billion years, American style,
or 13 -14 thousand million, British style).
The Big Bang.
12 billion years agoBeginnings of stars, heavy elements.
4.6 billion years agoSolar system forms by accretion.
4.5-4.4 billion years agoMolten Earth. Cobalt, nickel, iron migrate to center, form the core.
?4.4 billion years agoEarth is slammed by a large object, ejecting masses of debris. This orbiting debris accretes and forms our moon. (This scenario is the most widely accepted one at the moment.)
3.8 billion years agoFirst chemical fingerprints of life. (Prokaryotes: bacteria and related unicellular organisms lacking a well-defined nucleus.)
1.5 billion years ago Origin of complex (eukaryotic) cells.
1.0 billion years ago??Origin of sex??
550 million years agoThe "Cambrian explosion." Appearance of many complex forms of animals. Hooray for diversity!
440 million years ago (end of Ordovician).Diversity takes a beating from the first major extinction of species (about 85%). Cause: probably climate change resulting from shifting plates. Lots of land at the south pole; the Earth cools, and glaciers form.
365 million years ago (late Devonian). Another major extinction, this time primarily of marine organisms. Same causes?
230-250 million years ago (end of Permian).The big one! 96% of species go extinct. Pangaea exists. Massive volcanic eruptions form the Siberian Traps (steps), which may have caused the extinction. It's tectonics again!
205 million years ago (end of Triassic).75 % of species go extinct. Cause unclear.
65 million years ago (end of Cretaceous).Dinosaur extinctions. Probably from more massive volcanism (Deccan Traps, India), plus sea-level changes from plate movement, plus the asteroid.
4 million years ago."Lucy" (Australopithecus afarensis). Good candidate for the earliest ancestor of Homo, after the ape/human lineages split.
2 million years ago.Our genus (Homo) appears.
730,000 years ago.Last reversal of Earth's magnetic field.
100,000 years ago Anatomically modern humans in Africa.
40-50,000 years ago"Great Leap Forward." Abundant signs of culture, art, technology, etc.
40,000 years agoProbable colonization of Australia by aboriginals; oldest continuous human culture, now ending.
10,000 years agoOrigins of agriculture, eventually leading to human overpopulation (now).
3500 BCE (Before Current Era).Oldest generally accepted examples of written language (Sumeria).
19-20th century CE (Current Era).Beginnings of latest great extinction. This one is not a result of plate movements, etc. Rather, it is us humans that are responsible for what is likely to be extinction of a huge majority of species, and elimination of most wild habitats. Congratulations! : (

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