Always remember that you are absolutely unique. Just like everyone else.

Margaret Mead

IT IS DIFFICULT FOR US TO IMAGINE THE LONG TIME INTERVALS THAT HAVE PASSED IN THE HISTORY OF THE EARTH.

IF THE PLATES ARE SPREADING APART AT THE MID-ATLANTIC RIDGE AT A RATE OF 2 CM PER YEAR, THAT DOES NOT SEEM LIKE MUCH.

HOWEVER, IN ONE MILLION YEARS, THAT WORKS OUT TO BE:

1,000,000 X 2 = 2,000,000 cm or 20,000 meters

OR 20 KM

IN 100 MILLION YEARS, THAT WOULD BE

2,000 KM

FOR US TO EXPERIENCE ONE MILLION YEARS IS HARD TO IMAGINE.

IF YOU COULD LIVE FOR 100 YEARS, WHICH IS A VERY LONG LIFETIME, YOU WOULD HAVE TO LIVE 10,000 LIFETIMES TO EXPERIENCE ONE MILLION YEARS.

MODERN HUMANS HAVE ONLY BEEN AROUND LESS THAN 200,000 YEARS.

SCIENTISTS CAN DATE ROCKS BY USING THE NATURALLY OCCURING RADIOACTIVE ISOTOPES THAT ARE PRESENT IN THE ROCKS.

ATOMS WITH VERY LARGE NUCLEI TEND TO BE RACIOACTIVE.

THESE NUCLEI ARE NOT STABLE AND WILL DECAY (BREAK APART) TO FORM LIGHTER ELEMENTS.

EVERY ISOTOPE HAS A GIVEN HALF LIFE.

THE HALF LIFE IS THE TIME IN WHICH HALF THE ISOTOPE WILL DECAY.

FOR EXAMPLE, URANIUM 238 HAS A HALF LIFE OF 4.5 BILLION YEARS.

RADIOACTIVE DECAY EXAMPLE

CARBON 14 HAS A HALF LIFE OF ABOUT 5,700 YEARS.

SCIENTISTS ESTIMATE THE AGE OF THE EARTH AND THE SOLAR SYSTEM TO BE 4.5 BILLLION YEARS.

THAT’S A VERY LONG TIME, AND TIME FOR A GREAT DEAL TO HAPPEN.

THE SURFACE OF THE EARTH WAS VERY HOT FOR A LONG PERIOD OF TIME.

THE BIG UNITS OF TIME GEOLOGIST USE TO DIVIDE GEOLOGIC TIME INTO ARE EONS.

THE FIRST EON WAS THE HADEAN EON, WHICH WENT FROM THE BEGINNING OF THE EARTH (4.5 BYA) TO 3.8 BYA.

THE SECOND EON WAS THE ARCHAEN EON, WHICH WENT FROM 3.8 BYA TO 2.5 BYA.

DURING THIS TIME, THE EARTH COOLED AND OCEANS FORMED.

PRIMITIVE, SINGLE-CELLED ORGANISMS CAME INTO BEING.

THESE WERE CELLS WITHOUT A NUCLEUS - BACTERIA.

THE PROTEROZOIC EON GOES FROM 2.5 BYA TO 540 MYA.

DURING THIS TIME, MORE COMPLEX CELLS CAME INTO BEING - CELLS WITH NUCLEI.

AN INTERESTING CHANGE HAPPENED TO EARTH’S ATMOSPHERE DURING THE PROTEROZOIC EON.

EARTH’S ORIGINAL ATMOSPHERE WAS MOSTLY NITROGEN, CARBON DIOXIDE, WATER VAPOR AND SOME TRACE GASES.

BETWEEN 2.5 BYA AMD 1.2 BYA, THAT CHANGED.

CYANOBACTERIA AND ALGAE DEVELOPED THE ABILITY TO USE PHOTOSYNTHESIS TO USE CARBON DIOXIDE TO PRODUCE FOOD AND ENERGY.

OXYGEN WAS A WASTE PRODUCT OF THAT PROCESS.

OVER A PERIOD OF TIME, THE OXYGEN CONCENTRATION THAT WE HAVE IN OUR ATMOSPHERE TODAY DEVELOPED.

ONE RESULT OF THIS CHANGE IS THAT MOST OF EARTH’S IRON ORE IS CONTAINED IN ROCKS BETWEEN 2.5 BYA AND 1.2 BYA IN THE FORM OF HEMATITE, Fe2O3.

THE DISSOLVED IRON THAT WAS IN OCEANS, LAKES, AND STREAMS WAS OXIDIZED AND DEPOSITED AS SEDIMENT.

THE THREE EARLY EONS ARE GENERALLY LUMPED TOGETHER INTO A TIME PERIOD THAT WE REFER TO AS THE PRECAMBRIAN.

THE PRECAMBRIAN MAKES UP 88% OF ALL OF THE TIME THAT EARTH HAS EXISTED.

THERE ARE NOT MANY FOSSILS THAT EXIST FROM THIS TIME, EXCEPT FOR MICROFOSSILS, AS ALL OF THE ORGANISMS WERE SINGLE CELLS.

SOME ALGAE DID LEAVE STROMATOLITE FOSSILS.

CURRENT STROMATOLITES FROM COAST OF AUSTRALIA

FOSSIL STROMATOLITES

AT THE END OF THE PRECAMBRIAN AND THE BEGINNING OF THE PALEOZOIC ERA, MULTICELLLULAR LIFE TAKES OFF

BEFORE THE PALEOZOIC, THERE WERE NO ORGANISMS WITH HARD PARTS

THAT CHANGED IN THE PALEOZOIC

THE GREAT BURST OF LIFE THAT OCCURRED IS SOMETIMES REFERRED TO AS THE CAMBRIAN EXPLOSION.

SO MUCH HAPPENED IN THE PALEOZOIC ERA THAT SCIENTISTS HAVE DIVIDED IT INTO SIX PERIODS.

CAMBRIAN PERIOD - 545 BYA – 505 MYA

FIRST HARD BODIED ORGANISMS

TRILOBITES AND BRACHIOPODS PROMINENT

ORDOVICIAN PERIOD - 505 – 438 MYA

RISE OF FISH - FIRST VERTABRATES

SILURIAN PERIOD - 438 – 410 MYA

WAXY COATED ALGAE LIVE ON LAND

MILLIPEDES HAVE EVOLVED - FIRST LAND ANIMALS

ARMORED FISH

DEVONIAN PERIOD - 410 – 355 MYA

THE APPALACHIAN MOUNTAINS ARE FORMED VIA A PLATE TECTONIC COLLISION BETWEEN NORTH AMERICA, AFRICA, AND EUROPE

APPEARANCE OF PRIMITIVE SHARKS

CARBONIFEROUS PERIOD - 355 – 290 MYA

FERNS - FIRST PLANTS WITH ROOTS

PRIMITIVE INSECTS EVOLVE

RISE OF AMPHIBIANS

RISE OF REPTILES

PERMIAN PERIOD - 290 – 250 MYA

BEETLES AND WEEVILS EVOLVE

DIMETRODON

DICYNODON

GORGONOPSID