Some Major Events in the History of Life Authors: J.W. Schopf, A. Knoll, A. Nutman, J. Kasting, J. Brocks. Chapters in book: Bennett et al Ch. 4 & 5

Carbon Isotope Fractionation

Stromatolites (3.6 Ga)

Ancient Fossils Apex Chert (3.45 Ga) Bitter Springs (850 Ma)

More evidence for early life: Molecular Fossils What are molecular fossils (also called biomarkers)? molecules that are well-enough preserved (or whose degradation pathway and products are well-enough understood) that they can be used to indicate the presence of specific life forms in the rock record What molecules might be preserved in this way? Of the four major classes of large, complex, biomolecules, nucleic acids, proteins, lipids, and carbohydrates, some have potential as molecular fossils…

Some other important molecular fossils include porphyrins (chlorophyll, haem), sporopollenins, extremely resistant polymers that form the walls of pollen and spores; and lignin, a complex polymer of phenolic alcohols found in vascular plant tissues. These are not easily categorized into these four groups The most abundant ‘molecular fossil’ of all is kerogen: insoluble, high-molecular weight organic matter of uncertain composition Nucleic acids (RNA, DNA) Proteins Carbohydrates Lipids hydrolyse rapidly degrade quickly. In bones, collagen disintegrates rapidly; though small, compact proteins such as osteocalcin may survive largely intact. Chitin? Cellulose? Not much work on these Sterol lipids are often preserved well enough that their original chemical form can be deduced 

Carbon Cycle CO 2 (ATM)  CO 2 (Dissolved in Oceans) CO 2 (Dissolved in Oceans) + H 2 O  HCO 3 - HCO Ca ++  CaCO 3 (Limestone)

Oxygen Cycle 2.5 Ga ferric iron oxides: red beds

Banded Iron Formations

Banded Iron- Formations Red Beds Billions of years ago Oldest known microfossils

OXYGEN AND CARBON DIOXIDE IN THE EARTH’S ATMOSPHERE DURING ITS FIRST 4 BILLION YEARS Carbon Dioxide Oxygen Billions of years ago % 0.1% present level (0.037%) % 0.01% present level (21%) OXYGEN CARBON DIOXIDE

billion year old rocks in the Hamersley Range, Australia, where Brocks et al found cyanobacterial biomarkers. This supports the hypothesis that photosynthesis provided the oxidizing power to precipitate the Hamersley iron formation. Iron oxide layers give this rock its reddish hue Ancient molecular fossils – Brocks et al. 1999

Acritarchs 1.9 Ga The Rise of Oxygen allows the development of more complicated organisms Why??

Sepkoski Curves Studying variation in the fossil record allows you to spot extinction events