bio 1130 topic 3 — slide 1 topic 3 – age of the earth and life

BIO 1130 Topic 3 — Slide 1

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

The roots of extant Phyla go back into the Precambrian.


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


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!!


Extinct Burgess shale Phyla


Some survived


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.

Amphioxsus (Subphylum: Cephalochordata)


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.


TABLE 3-1: PARENT AND DAUGHTER ISOTOPESUSED IN RADIOMETRIC DATING

Method ParentIsotope

Daughterisotope

Half-life Effective datingrange

RubidiumStrontium

Rb-87 Sr-87 47 Gyr* 10 Myr** to 4.6 Gyr

PotassiumArgon

K-40 Ar-40 1.3 Gyr 100,000-4.6 Gyr

UraniumLead

U-238 Pb-206 4.5 Gyr 10 Myr – 4.6 Gyr

UraniumLead

U-235 Pb-207 71.3 Myr 10 Myr – 4.6 Gyr

ThoriumLead

Th-232 Pb-208 14.1 Gyr 10 Myr – 4.6 Gyr

Carbon-14Nitrogen-14

C-14 N-14 5,730 years 100 – 100,000 years

*Gyr = gigayears or billions of years**Myr = millions of years #13


Big Bang (Origin of the Universe) - 14 Gyr (gigayears) or Bya (billions of years ago)Formation of our solar system - 5 GyrPrecambrian 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 MyaCambrian Period: 540 Mya to 488 Mya - Burgess forms andTommotian fauna - virtually all extant phyla representedOrdovician Period: 488 Mya to 444 MyaPermian Period: 300 Mya to 251 Mya

Mesozoic Era: 250 Mya to 65 MyaCretaceous: 135 Mya to 65 Mya

Cenozoic Era: 65 Mya to present

SOME IMPORTANT TIMES


MASS EXTINCTIONS

Ordovician: 444 Mya Permian: 250 Mya end-Cretaceous: 135

Mya to 65 Mya


Evidence for life in rocks 3.8 Gyr old

#10How much 13C?

bio 1130 topic 3 — slide 1 topic 3 – age of the earth and life

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