Download 1)Extraterrestrial

Ch. 11 History of Life on Earth
How did Life Begin?
-There are 3 different theories :
1)Extraterrestrial
 Life formed on a planet outside our solar system. Then, life
was carried here on a meteorite or asteroid. (This theory is not
testable – there is no experiment that can be done to test its
validity)
2)Creation
 Life was put on Earth by a Divine Force. (This theory is also
not testable—there is no experiment that can be done to test
its validity)
3)Origin from nonliving matter
 Life arose from inanimate (non-living) matter when the
circumstances were favorable (there was enough water, right
temperature, enough oxygen and other chemicals and elements
present to create and sustain life)
 It has been determined that the Earth is 4.5 Billion years old
(4,500,000,000 years old)
 So 4.5 billion years ago, the planet was a moderate temperature,
there was liquid water, and it was large enough to exert a
gravitational pull to hold a protective atmosphere – BUT THERE
WAS NOT ENOUGH DENSITY IN THE CLOUDS OR UPPER
LEVELS OF THE ATMOSPHERE TO BLOCK OUT SOLAR
RADIATION (UV RADIATION FROM SUN)
 For this reason, any life that started, would start in water so as to
have protection from the solar radiation.
 Oldest Fossils were found in a rock that is 3.5 billion years old. (The
rock was once sediments on the ocean floor) The fossil is of
BACTERIA.
 The earliest life was bacteria – There were 2 groups
 EUBACTERIA –“TRUE BACTERIA” – most common bacteria
today
 ARCHAEBACTERIA –“ANCIENT BACTERIA” – today, most
of the archaebacteria live in extreme environments (salty lakes,
hot springs, swamps, stomach and intestinal tract of humans and
some animals)
 CYANOBACTERIA – group of photosynthetic bacteria that evolved
3 billion years ago.
 They released Oxygen into the ocean. This Oxygen then began to
bubble up into the air  billions of years passed, more and more
Oxygen added to the atmosphere to give us the atmosphere we
have today.
 1.5 Billion years ago, the first Eukaryotic cells evolved.
ANCESTRAL CELL
ARCHAEBACTERIA
EUBACTERIA
PROTIST
ANIMALS
PLANTS
FUNGI
 At least 5 times during the history of life, a large percentage of
existing species have become extinct within a short period of time.