YOU ARE HERE!

FOR STAR TREK FANS YOU ARE HERE

THE DISTANCES IN SPACE ARE AMAZING. EARTH IS 93,000,000 MILES FROM THE SUN. AT THE SPEED LIGHT TRAVELS (186,000 MILES/SECOND OR 6.7 X 10 8 MILES/HOUR) SO, IT TAKES 8.3 MINUTES FOR LIGHT FROM THE SUN TO REACH EARTH. THE NEAREST STAR TO THE SUN IS 4.2 LIGHT YEARS AWAY. THAT’S 2.5 X MILES AWAY

OUR GALAXY IS 100,000 LIGHT YEARS ACROSS. THAT’S 5.9 X MILES. DISTANCES ARE SO GREAT THAT IF THERE IS INTELLIGENT LIFE ON OTHER WORLDS, IT WOULD BE HIGHLY UNLIKELY THAT WE WOULD EVER KNOW. THEN, IF THERE IS INTELLIGENT LIFE ON OTHER WORLDS, WHY WOULD IT WANT TO CONTACT US?

LET’S CONSIDER THE PROBABILITIES. IN OUR GALAXY, THERE ARE 200,000,000,000 STARS. SCIENTISTS EXTIMATE THAT THERE ARE 200,000,000,000 GALAXIES. SO, THAT MAKES 4 X STARS. WITH THAT NUMBER, ONE WOULD EXPECT THAT THERE MUST BE OTHER WORLDS WITH LIFE. THEN, ONE MIGHT ASK THE QUESTION, WOULD IT BE JUST LIKE OUR LIFE?

LIFE EXISTS ON EARTH AS IT IS IN THIS MOMENT BECAUSE OF A SERIES OF EVENTS. FIRST, LET’S CONSIDER THE FORMATION OF THE SOLAR SYSTEM. “SCIENTISTS ESTIMATE THAT THE DUST CLOUD THAT OUR SOLAR SYSTEM FORMED IN WAS AT LEAST 24 BILLION KILOMETERS ACROSS AND CONTAINED MATERIALS FROM AT LEAST TWO PREVIOUS GENERATIONS OF STARS.” “You Are Here, A Portable History of the Universe,” Christopher Potter

ONCE THE SUN STARTED TO CONDENSE, EVENTS HAPPENED RAPIDLY. IN APPROXIMATELY 100,000 YEARS, THE SUN CONDENSED AND IGNITED. 99.9% OF THE MATERIAL IN THE DUST CLOUD WENT TO FORM THE SUN. THE REMAINING MATERIAL WAS IN A DISC AROUND THE SUN AND WENT TO FORM THE OTHER OBJECTS IN THE SOLAR SYSTEM. AFTER ABOUT 1,000,000 YEARS, THE REMAINING DUST WAS CONDENSING INTO PLANETS, MOONS, AND ASTEROIDS.

THE DUST DISK AROUND THE SUN ROTATED IN THE SAME DIRECTION AND CONTINUES TO DO SO AFTER IT IS FORMED INTO PLANETS. AFTER ABOUT 10 MILLION YEARS AFTER REACHING FINAL MASS, EARTH IS STRUCK BY A MARS SIZED OBJECT. THE TWO IRON CORES MERGE, AND A LARGE AMOUNT OF THE ROCKY CRUST IS THROWN INTO SPACE AROUND THE EARTH. THIS MATERIAL FORMS THE MOON. Formation of the moon

THE MOON STABILIZES THE EARTH AND KEEPS IT FROM WOBBLING ON ITS AXIS. IF THE MOON DID NOT EXIST, EARTH WOULD WOBBLE MORE ON ITS AXIS, AND SEASONS WOULD CHANGE MORE OFTEN AND LESS PREDICTABILLY. AFTER ABOUT 500,000,000 YEARS, BOMBARDMENT WAS ALMOST OVER. CURRENTLY, THE PROBABILITY OF EARTH BEING HIT BY A MAJOR OBJECT IS ABOUT ONCE EVERY 30 MILLION YEARS. THE PROBABILITY OF BEING HIT BY A SMALL ONE IS ONCE EVERY 1000 YEARS.

CURRENT NEAR MISSES From AsteroidDate(UT)Miss DistanceSize 2006 RO36Jun LD1.2 km 2001 PJ9Jul LD1.1 km 2006 BL8Jul LD48 m 2003 DZ15Jul LD153 m 2005 WK4Aug 98.1 LD420 m 1999 CF9Aug LD1.1 km 2002 JR9Aug LD1.4 km

JUPITER PROTECTS EARTH FROM BOMBARDMENT, AS WELL. THE MOON HAS BEEN MOVING AWAY FROM THE EARTH AT ABOUT 38 MILLIMETERS PER YEAR, AND, IN TURN, SLOWING DOWN THE EARTH’S ROTATION.

THEN, THERE IS WATER. A HUGE AMOUNT OF WATER ARRIVED ON EARTH EARLY IN EARTH’S HISTORY. POSSIBILITIES INCLUDE 1)WATER FROM VOLCANOES 2)WATER FROM SMALL COMETS AND ASTEROIDS EARTH RECEIVES ABOUT 30,000 TONS OF WATER EACH YEAR FROM COMET DUST.

“WITHOUT WATER, IT’S ALL JUST CHEMISTRY, BUT ADD WATER AND YOU GET BIOLOGY.” - Felix Franks, Univ. of Cambridge -

LET’S TAKE A LOOK AT HOW CONDITIONS ON EARTH HAVE SHAPED LIFE ON EARTH. 1)TO GET THE ELEMENTS WE HAVE ON EARTH, THE MATERIAL THAT FORMED OUR SOLAR SYSTEM WAS INVOLVED IN TWO PREVIOUS GENERATIONS OF STARS. 2)COLLISION WITH A MARS SIZED BODY CONTRIBUTED TO EARTH’S METALLIC CORE. 3)EARTH’S MOLTEN METALLIC CORE GIVES EARTH A MAGNETIC FIELD, WHICH PROTECTS EARTH FROM BOMBARDMENT BY PARTICLES FROM THE SUN.

4) EARTH’S CORE IS STILL MOLTEN BECAUSE OF THE HEAT GENERATED IN THE FORMATION OF THE EARTH AND THE PRESENCE OF RADIOACTIVE ELEMENTS. 5) THE COLLISION WITH A MARS SIZED BODY GAVE EARTH A LARGE MOON. 6) THE MOON STABILIZES EARTH AND KEEPS IT FROM WOBBLING ON ITS AXIS. THIS GIVES EARTH REGULAR SEASONS. 7) ABOUT 2 BILLION YEARS AGO, BLUE GREEN ALGAE DEVELOPED IN EARTH’S OCEANS. THEY PRODUCED OXYGEN AS A WASTE PRODUCT. THIS LED TO OXYGEN IN THE STRATOSPHERE, AND, IN TURN, OZONE.

8) OZONE IN THE STRATOSPHERE BLOCKS UV RADIATION AND ALLOWED LIFE TO DEVELOP ON LAND. 9) HAVING JUPITER OUTSIDE OF EARTH’S ORBIT MEANS THAT EARTH RECEIVES FEWER COLLISIONS WITH DEBRIES FROM OUTER SPACE. 10) WE HAVE LOTS OF WATER. 11) OUR CURRENT ATMOSPHERE REPRESENTS AN EQUILIBRIUM BETWEEN GREEN PLANTS AND ANIMALS.

WHAT ELSE MIGHT HAVE CONTRIBUTED TO LIFE AS WE KNOW IT ON EARTH?

ONE BIG FACTOR HAS BEEN THE MAJOR EXTINCTIONS THAT HAVE OCCURRED. WE HAVE HAD 5 MAJOR EXTINCTIONS THAT SCIENTISTS KNOW ABOUT. EACH TIME AN EXTINCTION OCCURS, EVOLUTION KICKS INTO HIGH GEAR TO FILL THE NICHES LEFT VACANT. EXTINCTION IS THE RULE OF EVOLUTION AND SURVIVAL THE EXCEPTION. THE AVERAGE AGE OF A SPECIES IS ABOUT 4 MILLION YEARS.

WOULD LIFE ON EARTH AS WE KNOW IT BE AS IT IS IF ALL OF THESE EVENTS HAD NOT HAPPENED?

DO MODERN HUMANS REPRESENT THE PEAK OF EVOLUTION?

ASTRONOMERS FINALLY HAVE TECHNIQUES TO SEARCH FOR PLANETS AROUND OTHER SUNS, AND THEY ARE FINDING A NUMBER OF THEM – SOME EARTH SIZED. IF THERE IS LIFE ON OTHER WORLDS, WOULD YOU EXPECT IT TO BE SIMILAR TO WHAT WE HAVE?