Evolution of the Earth Seventh Edition Prothero Dott Chapter 9 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Early Life and its Patterns Origin of Life – early work and controversies, potential mechanisms for abiogenesis Record of early life- what do they tell us about Earth at the time? The major players? Cambrian explosion - Earth's effect on life, life's effect on Earth

Origin of Life: Early Ideas Spontaneous Generation – process of putrefaction somehow producing metamorphosis of nonliving to living matter Louis Pasteur's sealed flask experiments

If life doesn't spontaneously generate now, how could it in the past? - Conditions on Earth were different bya – Composition of the atmosphere (reducing vs oxidizing), forms of nutrients, conditions of the oceans, temperatures etc. Life radically changed the Earth. – “Warm Little Pond” - Primordial Soup (CH4, NH3, CO2, N2 rich) – Intense UV bombardment (no ozone) – Late Heavy Bombardment ( bya)

Fig. 9.2 (Atm of H2, CH4, NH3)

What about polymers? Simplest cells have more complex organic molecules Polymer – complex chains of linked simple organic molecules (proteins, nucleic acids, sugars, fats, enzymes) Experimentally derived in a number of ways – splashing amino acids under hot, dry conditions forming proteins (Sidney Fox) – Cyanide, clays, and heat capable of polymerizing amino acids into proteins – Can form nucleotides under similar conditions (heating of ammonium and cyanide – Miller)

Cell membranes? Formed from fatty acids - carboxyl group (COOH) and aliphatic chain Fatty acid + alcohol form lipids Lipids form cell membranes that regulate what goes in an out of a cell Actually easy to synthesize as well as found on meteorites Chicken or Egg – RNA vs Proteins?

Fig. 9.4 Lipid Bilayer

Fig. 9.5 Protenoids: behave much like bacteria, regulate their cells, excrete waste, metabolize sugars

Fig. 9.1 (3.6 bya)

What about the rock record? Fig. 9.6 Thermophiles, chemosynthetic, hydrothermal vents vs cyanobacteria (both prokaryotes)

Fig. 9.7

Fig. 9.8f 3.4 by stromatolite – Swaziland Supergroup, South Africa

Fig. 9.8g, Modern filamentous cyanobacteria, Lyngbya – cells are identical to those of Warrawoona Group

Fig. 9.8h – 4 celled cyanobacteria 1.55 bya

Fig. 9.8i Modern colonial cyanobacteria, Gloecapsa

Fig – More complex eukaryotes developing from symbiotic relationships between prokaryotes - Symbiotic origin of Eukaryotes around 1.75 ba, didn't diversify much until 1.1 bya (sexual reproduction?)

Fig. 9.11abc Ediacaran metazoan trace fossils ( ma)

Why don't we find more Pre- Cambrian fossils? Most transitions between pre-Cambrian rocks and Cambrian have a profound unconformity, many pre-Cambrian rocks are metamorphosed Most Ediacaran metazoans are soft bodied animals (hard to preserve)

Cambrian Explosion (540 ma) Soft bodied organisms replaced with many fossils of shelled invertebrates Significant amounts of burrowing/trace fossils Large diversification of fossil record Likely related to the end of the extreme Varangian glaciation and increased tectonic rifting

Fig Early Cambrian shelled fossils thought to be related to sponges, corals, or molluscs

Fig. 9.14

Additional contributors to the Cambrian Explosion Potentially higher atmospheric O2 (size of metazoans) Increased nutrients associated with more rifting and volcanic activity Calcite secretion; phosphate and silica exoskeletons easier to synthesize under low atm. O2 Abundant cyanobacterial mats for molluscs and other small invertebrates to graze Development of predators Tiering of biotic activity on the sea floors

Fig. 9.15

Fig. 9.16a Ollenellus Free tail spines

Fig. 9.16b Ogygopsis tail spines fused into single plates

Fig. 9.16c Paradoxides

Fig. 9.16d Elrathia Juveniles to adults

Fig. 9.16e agnostids, blind trilobites, possibly floated

Fig. 9.17

Fig Helioplacus “experimental” echinoderm

Burgess Shale Middle Cambrian from Field, British Columbia (discovered in 1909) Abundant fossils of soft bodied animals, highly preserved Provides a rare glimpse at the diversity of soft-bodied organisms that are rarely preserved Highly experimental forms

Fig. 9.22a

Fig. 9.22b