THE TREE OF LIFE Gustav Klimt, 1909

OFTEN, THE RELATIONSHIP BETWEEN SPECIES THROUGH EVOLUTION IS PICTURED AS A TREE WITH THE ANCESTOR SPECIES LOWER ON THE TREE AND THE MORE RECENT SPECIES AS THE NEWER SMALL BRANCHES. WHERE A BRANCH OCCURS INDICATES A COMMON ANCESTOR.

Assyrian, 1000 BCE

GEOLOGIC TIME HADEAN ERA billion years ago to 3.8 bya ARCHAEN ERA- 3.8 bya to 2.5 bya PROTEROZOIC ERA bya to 543 mya PALEOZOIC ERA mya to 248 mya MESOZOIC ERA mya to 65 mya CENOZOIC ERA - 65 mya to today WE’LL ALSO BE CONCERNED WITH SOME OF THE SMALLER DIVISIONS, PERIODS, IN THE PALEOZOIC AND MESOZOIC ERAS.

DURING THE HADEAN ERA, THE EARTH WAS STILL PICKING UP MATERIAL FROM SPACE, AND THE SURFACE WAS MOLTEN FOR MUCH OF THIS PERIOD. SOME TIME DURING THIS PERIOD, THE SURFACE SOLIDIFIED. THERE ARE NO ROCKS ON EARTH THIS OLD. THE OLDEST ROCKS DATE TO ABOUT 3.8 BYA AT THE START OF THE ARCHAEN ERA. DURING THE ARCHAEN ERA, LIFE FIRST APPEARS ON EARTH IN THE FORM OF PRIMITIVE BACTERIA.

NO ONE KNOWS EXACTLY HOW LIFE FIRST BEGAN ON EARTH, BUT MOST AGREE IT BEGAN IN THE OCEANS THAT FIRST FORMED AFTER THE SURFACE COOLED AROUND 3.8 BILLION YEARS AGO. THE EARLY OCEANS WERE LIKELY A SOUP OF CHEMICALS. SOME OF THESE CHEMICALS EVEN CAME FROM OUTER SPACE IN THE FORM OF CHONDRITES, CARBON-CONTAINING METEORITES. AN EXAMPLE WOULD BE THE MURCHESON METEORITE FOUND IN AUSTRALIA.

UNDER THE RIGHT CIRCUMSTANCES, CERTAIN CHEMICALS ARE SELF ORGANIZING. AN EXAMPLE WOULD BE FATTY ACIDS AND LIPIDS. WHEN SHAKEN IN WATER, THEY CAN FORM SPHERICAL DROPLETS OF LIPID BILAYERS WHICH COULD SERVE AS PRIMITIVE CELL WALLS. SCIENTISTS HAVE ALSO DISCOVERED THAT RNA CAN SERVE AS CHEMICAL CATALYSTS AS WELL AS CONTAINERS OF GENETIC INFORMATION.

GEOLOGISTS HAVE DISCOVERED MICRO- FOSSILS AND CHEMICAL EVIDENCE DATING TO AROUND 3.5 BILLION YEARS AGO. THESE WERE FOUND IN ROCKS FROM MARINE SEDIMENTS.

DURING THE PROTEROZOIC ERA (2.5 bya to 543 mya), EUKARYOTIC CELLS APPEAR - PROBABLY AROUND 1.8 bya. SOME OF THESE HAVE THE ABILITY TO PRODUCE OXYGEN AS A WASTE PRODUCT, SO OXYGEN BUILDUP BEGINS IN THE ATMOSPHERE. OXYGEN EQUILIBRIUM WAS PROBABLY REACHED AROUND 2 bya.

THE PALEOZOIC ERA FOLLOWED (543 mya to 248 mya. TWO MAJOR EVENTS CHARACTERIZED THIS ERA. AT THE BEGINNING, A LARGE EXPLOSION IN MULTICELLULAR ORGANISMS OCCURRED. ALMOST ALL LIVING ANIMAL PHYLA APPEARED WITHIN A FEW MILLION YEARS. SOME 400 mya PLANTS AND ANIMALS EMERGED ON LAND.

AT THE END OF THIS ERA, THE LARGEST MASS EXTINCTION IN THE HISTORY OF THE EARTH OCCURRED, THE PERMIAN EXTINCTION. 90% OF ALL LIFE WAS DESTROYED. THE MESOZOIC ERA FOLLOWED (248 mya to 65 mya). DINOSAURS, AS WELL AS MAMMALS, APPEARED DURING THIS ERA, AND PLANTS UNDERWENT A GREAT CHANGE. THE EARLY MESOZOIC WAS DOMINATED BY FERNS AND CYCADS. MODERN GYMNOSPERMS SUCH AS CONIFERS APPEARED IN THE MIDDLE OF THE ERA. BY THE END, MODERN ANGIOSPERMS APPEARED.

THE MESOZOIC ERA ENDED WITH ANOTHER LARGE MASS EXTINCTION - THE END OF THE AGE OF DINOSAURS. THE CENOZOIC ERA GOES FROM 65 mya TO THE PRESENT AND IS OFTEN REFERRED TO AS THE AGE OF MAMMALS. THE LAST 11,000 YEARS ARE CALLED THE HOLOCENE EPOCH. THIS REPRESENTS THE TIME SINCE THE LAST ICE AGE.

MAJOR EXTINCTIONS LATE CAMBRIAN - APPROX. 500 mya - A SERIES OF EXTINCTIONS AS A RESULT OF A CHANGE IN SEA LEVEL LATE ORDOVICIAN - APPROX 440 mya - TWO PEAK EXTINCTIONS - THE FIRST AS A RESULT OF GLACIATION AND THE SECOND AS A RESULT OF RISE IN SEA LEVEL AT THE END OF GLACIATION LATE DEVONIAN - OVER A PERIOD OF ABOUT 3 MILLION YEARS, 365 mya 70% OF ALL SPECIES WERE LOST - FACTORS SUGGESTED INCLUDE GLOBAL COOLING AND A DROP IN OXYGEN LEVELS IN THE SHALLOW SEAS.

PERMIAN EXTINCTION - LARGEST EXTINCTION EVENT - EXTIMATED THAT AS MANY AS 96% OF ALL MARINE SPECIES WERE LOST AND 75% OF ALL VERTEBRATE FAMILIES ON LAND - THE MOST IMPORTANT FACTOR SEEMS TO BE CLIMATE CHANGE. END CRETACEOUS EXTINCTION (KT EXTINCTION)- 85% OF ALL SPECIES DISAPPEARED, INCLUDING THE DINOSAURS - THEORIES SUGGEST A LARGE METEORITE.

WHY SHOULD WE BE CONCERNED ABOUT PAST EXTINCTIONS?

1.WHAT HAPPENED IN THE PAST COULD HAPPEN IN THE FUTURE. A.CLIMATE CHANGE B.ASTEROID/COMET COLLISION 2. GIVES CLUES AS TO HOW EXTINCTIONS DROVE EVOLUTION 3. PROVIDES INFORMATION AS TO HOW LIFE MIGHT DEVELOP ON OTHER WORLDS

SCIENTISTS NOW TALK ABOUT A SIXTH EXTINCTION THAT COULD BE TAKING PLACE NOW. WHILE NOT IN TOTAL AGREEMENT, SCIENTISTS ESTIMATE THAT BETWEEN 17,000 AND 100,000 SPECIES ARE LOST EACH YEAR. IF WE ASSUME A MID-RANGE NUMBER OF 50,000, THAT WOULD MEAN A LOSS OF 50% OF EARTH’S SPECIES IN 100 YEARS.

RICHARD LEAKEY AND ROGER LEWIN IN THEIR BOOK “THE SIXTH EXTINCTION” GIVE THREE REASONS WHY THIS IS OCCURING: 1.DIRECT EXPLOITATION 2.DESTRUCTION AND FRAGMENTATION OF HABITAT 3.INTRODUCTION OF ALIEN SPECIES WE SHOULD PROBABLY ADD A FOURTH FACTOR - CLIMATE CHANGE.

WHAT IS DRIVING THE 6 TH EXTINCTION?

1 DOT = 7,500 PEOPLE

IT SHOULD BE POINTED OUT THAT THE COMPOSITION OF OUR ATMOSPHERE IS NOT AN ACCIDENT. IT IS A RESULT OF A NUMBER OF BIOLOGICAL FACTORS WORKING TOGETHER TO PRODUCE THE ATMOSPHERIC COMPOSITION THAT WE HAVE NOW. 1.GREEN PLANTS PRODUCING OXYGEN AND USING CARBON DIOXIDE 2.A CERTAIN AMOUNT OF CARBON TIED UP IN ORGANIC MATERIAL 3.A CERTAIN AMOUNT OF CARBON TIED UP IN ROCKS

THERE ARE POSSIBLY TWO FACTORS THAT CONTROL THE FATE OF LIFE ON EARTH: 1.THE SURFACE TEMPERATURE 2.THE CONCENTRATION OF CARBON DIOXIDE GAS IN THE ATMOSPHERE

FIRE AND ICE Some say the world will end in fire, Some say in ice. From what I’ve tasted of desire I hold with those who favor fire. But if it had to perish twice, I think I know enough of hate To know that for destruction ice Is also great And would suffice. - Robert Frost -