Transcript THE TREE OF LIFE

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 - 4.5 billion years ago to 3.8
bya
ARCHAEN ERA- 3.8 bya to 2.5 bya
PROTEROZOIC ERA - 2.5 bya to 543 mya
PALEOZOIC ERA - 543 mya to 248 mya
MESOZOIC ERA - 248 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 MICROFOSSILS 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 6TH
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 -