Life on Earth Topic 6 : Evidence Suggesting When Life Originated

1. Life on EarthTopic 6: Evidence Suggesting When Life Originated Part of the Evolution of Australian Biota Module Biology in Focus, Preliminary Course Glenda Childrawi and Stephanie Hollis

2. DOT Point • Describe some of the palaeontological and geological evidence that suggests when life originated on Earth • Explain why the change from an anoxic to an oxic atmosphere was significant in the evolution of living things uhh.hawaii.edu

3. Introduction Palaeontology is the scientific study of fossils and all aspects of extinct life. Geology is the scientific study of the origin, history and structure of the Earth as recorded in rocks. These two studies are valuable in combination to produce evidence from the past. 5garofolis.blogspot.com

4. Palaeontological Evidence The discovery of two 3400-3500 million year-old Precambrian fossils from Western Australia provided some of the first evidence towards the origin of life on Earth. • Fossils of single celled anaerobic procaryotes (microfossils) found were very similar to those found living today • Fossilised remains of stromatolites provided valuable information about the structure of early organisms sciencedirect.com

5. Palaeontological Evidence Simple bacteria existed in structures called stromatolites which were very similar to present day living stromatolites. These organisms live in shallow marine environments. Colonies of simple bacteria, or cyanobacteria, trap layers of calcium carbonate and ‘grow’ upwards in columns towards the sun. livelikedirt.blogspot.com

6. Palaeontological Evidence Deposits of living stromatolites can be found in Western Australia at Shark Bay, growing at a rate of about 1mm per year with individual domes reaching a diameter of about 200cm and a height of about 50cm. geol.umd.edu

7. Palaeontological Evidence The 1999 discovery of what could be the remains of nanobacteria or nanobes, in a meteorite from Mars (found in Antarctica) indicated similarities to nanobes discovered in Queensland in 1996. maybusher.com

8. Palaeontological Evidence Nanobes are filiment-type structures found in rock. The nanobes found on Mars were able to withstand radiation, cold and acidic conditions, a time when the environment on Mars may have paralleled that existing on Earth for a few hundred years. serc.carleton.edu

9. Palaeontological Evidence Given the presumed sharing of debris generated from meteorite impacts amongst the early planets, the origins of the nanobes on Mars and Earth may be the same. coolhunting.com

10. Palaeontological Evidence Some scientists hypothesise that nanobes are the smallest form of life (they are 10 times smaller than our smallest bacteria). However, some researchers believe nanobes to be merely crystal growths. The debate continues! tvt.cbi.uni-erlangen.de

11. Palaeontological Evidence In general, palaeontologists using the fossil evidence from different rock layers have found that the more primitive cells and marine organisms are found in the lower layers of rock compared to the more complex and land-dwelling organisms. explanet.info

12. Palaeontological Evidence This trend suggests that simple organisms evolved into more complex organisms and marine organisms preceded land-dwelling organisms. We can make inferences about extinct organisms by studying their closest modern living relatives. museumwales.ac.uk

13. Palaeontological Evidence 2500 million year-old Archaean rocks from north Western Australia were examined by scientists in 1999. They found biomarkers or chemical evidence, for the existence of cyanobacteria. Biomarkers are chemicals that are produced by only one group of organisms providing evidence of their existence in the past. bushheritage.org.au

14. Palaeontological Evidence Oxidised rocks such as banded iron and red bedrock formations provide geologic evidence towards the origin of photosynthetic life. ecosystems.wcp.muohio.edu

15. Change of Atmospheric Gases Photosynthetic life changed the world forever. For the first time, Carbon Dioxide was being removed from the atmosphere and free oxygen was being added. greentechmedia.com

16. Change of Atmospheric Gases An anoxic atmosphere is one defined as being deficient, or lacking, in oxygen. An oxic atmosphere is one where oxygen is available. A change from an anoxic to anoxicatmosphere with plenty of free oxygen had a significant influence on the conditions of early Earth and the evolution of living things. cimss.ssec.wisc.edu

17. Change of Atmospheric Gases Anerobic organisms began to decline while photosynthetic organisms became more abundant. Today anerobic organisms only survive in environments with very low oxygen concentration, such as swamps, bogs, deep underground or in deep ocean hydrothermal vents. en.wikipedia.org

18. Change of Atmospheric Gases Aerobic organisms became more efficient in energy production (respiration) which led to an increase in activity and eventually led to an increase in complexity and size of these organisms aquaticscape.com

19. Change of Atmospheric Gases As the oxygen in the atmosphere accumulated, it started reacting with the sun’s ultraviolet radiation. The ozone layer (O₃) began to form and block out harmful radiation from the sun. en.wikipedia.org

20. Change of Atmospheric Gases This reduced the amount of ultraviolet radiation reaching the Earth’s surface and had significant influence on future organisms as it protected them from dangerous radiation and enabled them to move onto land! green-buzz.net

21. Homework -Students to complete DOT Point 2.3 green-buzz.net