1 Origin of the earth  Big bang happened 14 billion years ago.  Earth and Moon formed 4.5 billion years ago (4.5 X 10 )  Oldest rock is 3.9 billion years old No rock on earth is as old as the earth itself!  Oldest fossils are 3.8 billion years old 9

2 Origin of the earth  The Sun and the planets are formed from a cloud of cosmic dust and gas.  As the earth condensed, a stratification of its components took place.  Heavier materials, moved into the center while lighter concentrated near the surface.  A crust formed, floating on the hot molten interior.

3 The early atmosphere  It is thought to have been principally composed of: N2 Co2 CO H2O H2  Also thought to have been present: H2S CH4

4 The early atmosphere  The early atmosphere is said to be a reducing atmosphere because it is thought to have contained much hydrogen which easily donates electrons (reduction).  In a reducing environment it takes little energy to form carbon rich molecules.

5 The early atmosphere  What gas is conspicuously absent in the early atmosphere?  When and by what means did this gas become 1/5 of today's atmosphere?

6 The early oceans  The early oceans are thought to have been formed when the earth cooled and the gaseous H2O fell in torrential rains on the crust.  They must have had dissolved salts and minerals from the land around them and dissolved gasses from the atmosphere.  And soon organic materials were added.

7 The Miller - Urey experiment  They tested a theory first put forward by the Russian Alexandr Oparin.  They tested whether it was possible to get organic compounds in an experiment that re-created the conditions around the early earth.  They succeeded in getting organic gasses and simple organic acids and amino acids in solution.

8 The origin of life  Divide into 5 groups  Each group explores one possible theory on the origin of life 1. Special/divine creation 2. Spontaneous creation 3. Panspermia, arrival of material from outer space. 4. Primitive soup, abiotic replication of RNA. 5. Steady state.

9 Clay as a catalyst  Aharon Katchalsky (worked in Israel) found that certain types of clay could catalyse the formation of polypeptides from amino acids. This supported the ideas that life did need something like a clay catalyst at the beginning because the oceans were too diluted.

10 The Cairns-Smith´s theory ( or clay creation)  First “organisms” were made of minerals.  Basic material is silica acid, Si(OH)4, in clay. It easily polymerises not uniform, can be straight or branching (with occasional minerals Mg+2, Al+3, Fe+2) diverse infrastructure crystal genes were formed

11 The hen or the egg?  “DNA makes RNA makes Protein”  What was the first molecule that could replicate itself?  Which of these three takes part in all the processes?

12 The RNA world  Ribose is more easily synthesised than deoxyribose.  RNA can act as a catalyst.  RNA can catalyse a complimentary strand of itself. a 52 nucleotide stretch of RNA can replicate itself  but RNA is not stable.

13 Coacervate droplets ( the basis of the first cells? )  Small spherical bubbles made of a bi-layered membrane.  Capable of absorbing substances from the surrounding solution facilitated chemical reactions exporting products.  Grow by accumulating sub- unit molecules from surroundings.  Divide by pinching, form buds.

14 Earliest cells  Fossils of Prokaryotes from around 3.8 billion years ago represent the earliest life forms known on earth.

15 Endosymbiotic theory Lynn Margulis (USA)  prokaryotes have been incorporated into the eukaryotic cell.  This theory explains f.ex. why mitochondria and chloroplasts : have a double membrane. have their own DNA, a ring like prokaryotes have smaller ribosomes have enzymes on their inner membrane related to prokaryotic enzymes divide by splitting in two

16 Endosymbiotic theory Lynn Margulis (USA)  This also means that it is from prokaryotes that the four eukaryotic kingdoms arise. K. Fungi K. Plants K. Animals K. Protists K. Prokaryotes