Transcript 22.4 – Early Life on Earth

22.4 – Early Life on Earth
Origin of Life
• Bombardment from outer space prevented
life from developing on Earth until at least
3.9 billion years ago (BYA)
• Where and how the first life-form
developed, however, remains an active
area of research
Origins of Life
• Earliest atmosphere contained hydrogen,
methane and ammonia
• This atmosphere + energy supplied by
lightning would give rise to organic matter
in shallow oceans
Primordial Soup
• Miller & Urey devised
an apparatus to test
this hypothesis in
1953
– Within one week their
apparatus had
produced organic
molecules
– Organic molecules
included amino acids,
the building blocks of
proteins (& life) http://www.pas.rochester.edu/~afrank/A105/LectureXVII/FG28_002.PCT.jpg
http://www.centauri-dreams.org/wp-content/uploads/2007/07/interstellar_chemistry.jpg
Other Scenarios
1. Amino acids organized
•
•
somewhere else in the
universe and were
brought to earth by
asteroids or comets
Chemical synthesis of
organic molecules is
possible in interstellar
clouds
Amino acids have been
found in meteorites
http://www.rsc.org/images/b820577a-350-FOR-TRIDION_tcm18-145077.jpg
Other Scenarios
2. Amino acids originated deep in Earth or
its oceans
• Conditions there are favorable for
chemical synthesis
• Organisms have been found at depths
exceeding 3 km
Other Scenarios
3. Possibility that life emerged deep in the
ocean at hydrothermal vents
http://www.divediscover.whoi.edu/images/vent_chemistry.jpg
http://www.astrochem.org/endoexo.jpg
Essential Characteristic of Life
• Ability to reproduce
• All cells require RNA
and DNA to reproduce
• Recent experiments
suggest that RNA
molecules might have
been the first
replicating molecules
on Earth
http://www.odec.ca/projects/2004/mcgo4s0/public_html/t3/DNA-RNA_strcture.gif
Proterozoic Life
• Nuclei are separate compartments that
contain RNA and DNA
• Prokaryotes = Organisms that do not
contain nuclei
• Eukaryotes = Organisms whose cells
contain RNA and DNA in nuclei
Simple Eukaryotes
• Can be unicellular or multicellular
• Because they contain nuclei and other
internal structures, they are larger than
prokaryotes
• Extinction came from a widespread
glaciation event 750 million years ago
(mya)
http://io.uwinnipeg.ca/~simmons/16cm05/1116/28-04-EukaryoteOrigin-L.gif
Multicellular Organisms
• About 630 mya, the climate warmed
dramatically and the first multicellular
organisms appeared in the oceans
• Fossils first discovered in 1947 in Australia
– Collectively called the Ediacaran biota, these
fossils show the impressions of large, softbodied eukaryotes.
Edicaran biota
• Seemed to answer
the question of why
there are no fossils
of organisms that
existed during the
first period of the
Paleozoic era
https://www.nampost.com.na/shop/products_pictures/eriacaran-fosils-2008.jpg
Edicaran Fossils
• In recent years, geologists have found
Ediacaran fossils in all parts of the world.
– Flourished between 630 mya and 540 mya.
• Mass extinction = most of them
disappeared
– More likely related to present-day organisms
began to inhabit the oceans
In-Class Assignment/Homework
• WKT 22.4
• AND pg. 641-2 #1-23
– Answer on the back of WKT 22.4