Transcript Life3
Early Life – the evidence •The oldest well dated and well preserved microsfossils are Apex Chert at Marble Bar, Western Australia dated at 3.465 billion years. Layered between volcanic flows which can be dated very accurately. •Microorganisms resemble cyanobacteria (bluegreen algae i.e. pond scum) •Planet was only a few hundred million years old at the time the Apex chert was formed. •Implication that as soon as life could arise it did arise. Apex Chert Formation Say hello to your ancestors !!! If Life needs water where did it come from? • Outgassing of volcanoes • Bombardment of Comets (icy snowballs) • Oceans = Comet Juice Primordial Soup Recipe • Solid surface • Water • Atmosphere of methane (CH4), ammonia (NH3), water (H2O), hydrogen sulfide (H2S), Carbon dioxide (CO2) or carbon monoxide (CO), and phosphate (PO43-). • “Reducing” atmosphere - No Oxygen !!!!!! • Lots of volcanism – raw materials / energy Miller – Urey experiment • 1953 – Harold Urey and Stanley Miller - University of Chicago • Water (H2O), methane (CH4), amonia (NH3), hydrogen (H2) and carbon monoxide (CO). The chemicals were all sealed inside a sterile array of glass tubes and flasks connected in a loop, with one flask half-full of liquid water and another flask containing a pair of electrodes. • The liquid water was heated to induce evaporation, electrical sparks were fired between the electrodes to simulate lightning. • Atmosphere was cooled again so that the water could condense and trickle back into the first flask in a continuous cycle. Miller – Urey experiment What Did they find? • One week of continuous operation – Dark “glop” formed in glassware. • Miller and Urey observed that as much as 10– 15% of the carbon within the system was now in the form of organic compounds. • Two percent of the carbon had formed amino acids with glycine as the most abundant – detected (5) amino acids originally – reanalysis with modern equipment detected (22)!! • Sugars, lipids, and some of the building blocks for nucleic acids were also formed. Problems • UV radiation would dissociate organic molecules on the surface (no ozone layer). • Atmosphere may have been different than original model (controversial) • Have mechanism for forming building blocks, but not actual proteins and DNA Abiogenesis theories • • • • • • • • Hydrothermal vents Extraterrestrial origins RNA world hypothesis Clay Theory Ice-world Theory Thermosynthesis Many other theories Problem is that there are too many theories – no scientific consensus. • Perhaps more than one path for life to arise ? The upshot • All of your molecules with an atomic number greater than (3) came from the innards of a star. • Fossil evidence indicates that life arose very early in the Earth’s history • Building blocks of life (amino acids) can be easily synthesized from non organic compounds (Urey Miller experiment). • Formation of more complex molecules of life (DNA, proteins) has not been explained, but not for a lack of theories.