1. Origin of Life on Earth Chapter 25

2. Earth originated about 4.6 billion years ago. Cloud dust rocks, water vapor. Settled by 3.9 billion years ago (bya) First atmosphere was reducing. Water vapor, nitrogen and its oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide

3. How did life originate?  Abiotic (nonliving) synthesis of small organic molecules, such as amino acids and nucleotides  Joining of these small molecules into macromolecules including proteins and nucleic acids  Packaging of these molecules into “protobionts”, droplets with membranes that maintained an internal chemistry different from that of the surroundings  The origin of self replicating molecules that eventually made inheritance possible.

4. Chemistry, geology, physics – evidence of origin of life.

5. 1953 Urey Miller experiment (fig 4.2, 25.2). Abiotic synthesis of organic molecules possible.

6. By dripping solutions of amino acids onto hot sand, clay or rock, researchers have been able to produce amino acid polymers.

7. Protobionts – abiotically produced molecules surrounded by a membrane – like structure – (fig 25.3) Glucose-phosphate Phosphorylase Amylase Starch Maltose Phosphate Simple metabolismSimple reproduction 20  m

8. RNA was the first genetic material. Also carry out number of enzyme-like functions, can form variety of shapes and can replicate – Protobiont with RNA (limited genetic information) increased in number. RNA formed base for DNA template. DNA world – diverse life forms.

9. How do we know about the history of life?

10. Fossils accumulated in sedimentary rocks called strata. Bear evidence of macroevolution – major evolutionary events over large span of time, like photosynthesis, mass extinctions etc. Incomplete but substantial record of evolutionary changes.

11. 1 Accumulating “daughter” isotope Remaining “parent” isotope 2 1 4 1234 1 8 1 16 Ratio of parent isotope to daughter isotope Time (half-lives) Radiometric dating

12. Geological record: 3 eons – Archean, Proteozoic, Phanerozoic Phanerozoic has 3 eras marked by mass extinction events – Paleozoic, Mesozoic and Cenozoic.

14. Can also use the analogy of a clock Land plants Animals Paleozoic Meso- zoic Ceno- zoic Origin of solar system and Earth 41 23 Multicellular eukaryotes Single-celled eukaryotes Prokaryotes Atmospheric oxygen Proterozoic Eon Archaean Eon Humans Billions of years ago Key events in evolution of life: First single-celled organisms First eukaryotes Origin of multicellularity: Colonization of land

15. First single-celled organisms – 3.5 bya Prokaryotes Billions of years ago 14 3 2

16. Atmospheric oxygen Billions of years ago 1 4 3 2

17. First single-celled organisms – 3.5 bya. Stromatolites (prokaryotes binding film of sediments) - cyanobacteria oxygenated the atmosphere. 2.7 bya O 2 accumulated in the water and then in the atmosphere – evidence rusting of rocks

18. First eukaryotes: 2.1 bya – complex organization, organelles serial endosymbiosis. LE 26-13 Plasma membrane Cytoplasm DNA Ancestral prokaryote Endoplasmic reticulum Nuclear envelope Infolding of plasma membrane Engulfing of aerobic heterotrophic prokaryote Nucleus Cell with nucleus and endomembrane system Mitochondrion Engulfing of photosynthetic prokaryote in some cells Plastid Mitochondrion Ancestral heterotrophic eukaryote Ancestral photosynthetic eukaryote

19. Evidence of endosymbiosis: In mitochondria and chloroplasts -  Replication similar to prokaryotes  Single circular DNA molecule  DNA not associated with histone proteins  Ribosomes show similar sensitivity to antibiotics like bacteria  Ribosomes similar in size to those of bacteria.

20. Single- celled eukaryotes Billions of years ago 14 23

21. Origin of multicellularrity:  1.5 bya small algae and other primitive eukaryotes. Several ice ages for 30my  Cambrian explosion – 535 – 525 mya – major diversification – bigger organisms, adaptations for hunting and defense 10  m

22. Origin of multicellularity Multicellular eukaryotes Billions of years ago 14 23

23. Animals Billions of years ago 1 4 23

24. Colonization of land  500 mya  extensive land adaptations  tetrapods 365 mya  our human species 195,000 thousand years ago.

25. Continental drift: Movement of continental plates over time. By about 10 million years ago, Earth’s youngest major mountain range, the Himalayas, formed as a result of India’s collision with Eurasia during the Cenozoic. The continents continue to drift today. By the end of the Mesozoic, Laurasia and Gondwana separated into the present-day continents. By the mid-Mesozoic Pangaea split into northern (Laurasia) and southern (Gondwana) landmasses. At the end of the Paleozoic, all of Earth’s landmasses were joined in the supercontinent Pangaea. 0 65.5 135 251 Millions of years ago Cenozoic Mesozoic Paleozoic North America Eurasia Africa India South America Madagascar Australia Antarctica Laurasia Gondwana Pangaea

26.  Rearrange geography – dramatic effects on life.  All land – drained shallow coastal areas; vast interiors  Supercontinents break – once connected populations become geographically isolated  Mass extinctions ; thriving communities disappear; five events - most famous Cretaceous mass extinction 65.5 million years ago. (6th on the way?)  Adaptive radiation – explosion of diversity, species occupying all niches – large number of species; e.g. mammals originated about 180mya but worldwide adaptive radiation 65.5mya.