3.2 Fossils and the Evolution of life

1. 3.2 Fossils and the Evolution of life Major stages in evolution of life The changing atmosphere Other ideas about origins of life

2. Outcomes • Describe key steps in evolution of life, including the development of organic molecules, membranes, procaryotic and eurcaryotic organisms, colonial cells and multicellular organisms • Identify evidence that present-day organisms have evolved from ancestral organisms • Identify the geological and palaeontological evidence that suggests when the earliest life forms appeared on Earth • Explain the importance of the change from an anoxic to an oxic atmosphere on the evolution of living things • Outline how scientific knowledge may be in conflict with cultural understandings in relation to the origins of life

3. Major stages in evolution of life • Formation of organic molecules • Formation of membranes • Procaryotic cells (earliest type of fossil found; no nucleus) • Eucaryotic organisms( membrane-bound organelles and cell organelles • Colonial cells: daughter cells became bound together after division eg stromatolites • Multicellular organisms: cells showing specialisation within one organisms

4. Evolution of organisms • Starting from present-day diversity, we can trace back the evolutionary pathways of living organisms • Some appear to have changed greatly eg horses • Others did not change over time eg ; horseshoe crab • Some became extinct eg: dinosaur

5. Palaeontological and geological evidence of early life • Oldest sedimentary rocks on earth are 3800 million yrs old • Fossils found in sedimentary rocks Fossil evidence in very ancient rocks RARE compared with the abundance of fossils found in rocks over the 600 million yrs • Earliest fossils: 2 types:found in rocks 3400-3500 million yrs old in WA, Sth Africa and North America – microfossils (similar to present-day single-celled anaerobic procaryotes) - Stromatolites : layers of photosynthetic procaryotic cyanobacteria

7. Stromatolites • Thought to be extinct: only fossils found before 1990’s • 1990’s living stromatolites found in Shark Bay, WA. • Cells form a mat which traps a layer of sediment. • Cyanobacteria grow up through the sediment to forma new mat layer • Grow at a rate of about 1mm per year

8. Shark Bay, WA Stromatolites: present day

9. Heterotroph to Autotroph • 1st primitive cells were heterotrophic • Cells containing pigments formed .. Able to capture light and use it as energy source to make organic compounds (photosynthesis) • This led to massive reduction in carbon dioxide and increase oxygen which was taken up by rocks : oxidised rocks can be seen in ancient banded iron and red bed rock formations

10. The changing Atmosphere • All oxidised surface rock saturated with oxygen, oxygen began to build up in atmosphere. • UV radiation reacted with some of it to form ozone until a layer formed around earth, high in atmosphere • Shielded earth from UV rays so less reached earth: decrease in radiation =decrease in heat….. New organisms could form • Change from anoxic to oxic atmosphere meant that anaerobic organisms declined and as oxygen levels increases, more photosynthetic organisms flourished • Today, anaerobic organisms can only survive in low oxygen / high carbon dioxide environments eg: mud swamps, bogs, deep underground or in deep ocean hydrothermal vents

11. Deep ocean hydrothermal vent

12. Oxygen increased, organisms developed that could directly use the oxygen : aerobic organisms now using RESPIRATION • This allowed increase in their size and complexity • EUCARYOTIC cells evolved, as did multicellular plants and animals • CONDITIONS changed!!!! • Protection from UV radiation • Free oxygen in atmosphere • Liquid water

13. Other ideas about origins of life • Ideas often linked to religious or spiritual beliefs of a community/ culture • Creationism • Evolution • Chinese culture: P’an Ku 1st living being • Aboriginal culture: Dreaming • Greek cosmogenies • Others?