Transcript Bio 392 - Chapter 17-2 - Earth`s Early History

Chapter 17.2:
Earth’s Early History
Age of the Earth

It is estimated that the Earth
is 4.6 billion years old
– Theories of how the Earth was “born”
vary (IE – the Big Bang Theory)
– Elements arranged themselves according
to density
Least dense make up the atmosphere, most
dense make up the core
Earth’s Early
Atmosphere

Earth’s early atmosphere probably
contained hydrogen cyanide, carbon
dioxide, carbon monoxide, nitrogen,
hydrogen sulfide, and water
– All toxic gases except the
water
The Early Earth

It wasn’t until 4 billion years ago that
the first solid rocks formed

It wasn’t until 3.8 billion years ago that
the Earth was cool enough to have
liquid water
– So this is when the first oceans formed
Formation of Organic
Molecules

Early atmosphere allowed the
formation of organic molecules
– Did not have oxygen
– Would not form in today’s atmosphere
 Oxygen
is too reactive
 Bacteria would eat the molecules
Miller and Urey

Stanley Miller and Harold Urey
attempted to answer what the
Earth’s early atmosphere and
how life began
Filled an enclosed flask with
hydrogen methane, ammonia,
and water to represent the
atmosphere

– Passed electricity through
this mixture
The Results

Amino acids began to form after a
couple days
– Extensions of their experiments have also
shown to make nucleotides

Scientists think that these were the
first steps to life
The First Cells

Thought to have originated 200-300 million
years after oceans formed

Earliest cells called proteinoid microspheres
were created when organic molecules
became trapped in bubbles
Not alive but have some
characteristics of living cells
Oxygen-Free Life Forms

The first life forms are thought to have
evolved in oxygen free environments
approximately 3.5 billion years ago
Photosynthetic organisms evolved
in the oceans approximately 2.2 billion
years ago

Started pumping oxygen into the
atmosphere
Rusty Oceans

When oxygen mixed with iron in the
water, the oceans began to rust
– The iron oxide sank to the bottom of the
oceans giving us the iron ore deposits
that we use today
The Ozone Layer

The ozone layer formed when oxygen
began to accumulate in the atmosphere

Created a poisonous atmosphere where
most of the organisms became extinct
– Those that survived became the anaerobic
organisms that we know today or they evolved to
use oxygen
Endosymbiotic Theory

Belief is that eukaryotes formed approx. 2
billion years ago
– Prokaryotes “moved into” prokaryotic cells

Created a symbiotic relationship
– One group was able to use oxygen to make ATP

Mitochondria
– One group was able to use light to make sugars

Chloroplasts
Evidence of the
Endosymbiotic Theory

Membranes of mitochondria and
chloroplasts are similar to that of freeliving prokaryotes

Mitochondria and chloroplasts have
– DNA similar to bacterial DNA
– Ribosomes similar to those of bacteria
– Reproduce by binary fission
Sexual Reproduction

The use of sexual reproduction by
early organisms allowed evolution to
occur at a much quicker rate
– More gene shuffling