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TOPIC 3 – AGE OF THE EARTH AND LIFE

TOPIC 3 – AGE OF THE EARTH AND LIFE. Three Distinct Cambrian Fauna. All major extant phyla are present at the start of the Cambrian?? They must have been present and evolving during the pre-Cambrian Therefore, they did not arise suddenly at the start of the Cambrian

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TOPIC 3 – AGE OF THE EARTH AND LIFE

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  1. TOPIC 3 – AGE OF THE EARTH AND LIFE

  2. Three Distinct Cambrian Fauna • All major extant phyla are present at the start of the Cambrian?? • They must have been present and evolving during the pre-Cambrian • Therefore, they did not arise suddenly at the start of the Cambrian • The roots of extant Phyla go back into the Precambrian.

  3. Ediacaran fauna: - 570 mya • ancestors of modern post-Cambrian forms ? • an extinct line ? • controversy not yet settled.

  4. Burgess forms • Burgess shale (500 to 600 Mya) • some clearly related to animals that survived and diversified later • e.g. , snails, clams, and some types of worms. • compare with Ediacaran and Tommotian fauna • Diverse with many that went extinct very early (see next four slides) • One very big surprise!!

  5. Extinct Burgess shale Phyla

  6. Extinct Burgess shale Phyla

  7. Some survived

  8. Amphioxsus (Subphylum: Cephalochordata) The Earliest Recorded Chordate • Myotomes • Notochord • Why do humans exist? • Because Pikaia gracilins survived the Burgess decimation. • The survival of Pikaia was a contingency of just history. We are indeed an accident.

  9. Tommotian fauna • dating from the very beginning of the Cambrian (570 Mya) • hard body parts which fossilized easily • many but not all are clear relatives and precursors of modern forms.

  10. TABLE 3-1: PARENT AND DAUGHTER ISOTOPES USED IN RADIOMETRIC DATING *Gyr = gigayears or billions of years **Myr = millions of years #13

  11. SOME IMPORTANT TIMES • Big Bang (Origin of the Universe) - 14 Gyr (gigayears) or Bya (billions of years ago) • Formation of our solar system - 5 Gyr • Precambrian Eon- 4.6 Byr to 540 Mya • Archean: 4.6 Byr to 2.5 Byr, origin of life, Ediacaran fauna • Phanerozoic(Eon): 540 Mya to present – we are in this Eon now • Paleozoic Era: 540 Mya to 250 Mya • Cambrian Period: 540 Mya to 488 Mya - Burgess forms and • Tommotian fauna - virtually all extant phyla represented • Ordovician Period: 488 Mya to 444 Mya • Permian Period: 300 Mya to 251 Mya • Mesozoic Era: 250 Mya to 65 Mya • Cretaceous: 135 Mya to 65 Mya • Cenozoic Era: 65 Mya to present

  12. MASS EXTINCTIONS • Ordovician: 444 Mya • Permian: 250 Mya • end-Cretaceous: 135 Mya to 65 Mya

  13. Evidence for life in rocks 3.8 Gyr old How much 13C? #10

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