Transcript Ch 26: Early Earth and the Origin of Life

Chapter 16
Origin of Life
The Big Bang
Theory
Big Bang Details

Galaxies are collections of stars, gas and dust bound
together by their mutual gravity

Galaxies comprise the basic building blocks of the
Universe

When galaxies were born and how they evolved is
currently a very active topic.

At present, the Universe is thought to have been
created in the Big Bang, in which space and time
were created in a simple hot energetic, state, about 15
billion (15 x 109 ) years ago.
Radiometric
Dating
A technique to determine the age of items on
our planet
Carbon 14  Nitrogen 14 is used to date
fossils (good up to 50 000 yrs)
Uranium 238 – Lead 236 is used to date rocks
and is good to 4.5 billion years
Carbon-14 – used to date fossils

Carbon-14 (14C) a rare isotope of carbon, that has 6
protons and 8 neutrons
 14C
decays to 14N at a constant rate

Every 5,600 years half the 14C in a sample will emit a
beta particle (electron) and decay to 14N

Thus 5,600 years is called the half life of 14C

Because of 14C’s short half life, it is not useful for
dating million year old fossils, it is only accurate to
about 50,000 years
Half-lives
256 14C atoms
at time 0
Half-lives
128 14C and
128 14N atoms
after 5,600
years or
1 half-life
Half-lives
64 14C and
192 14N atoms
after 11,200
years or
2 half-lives
Half-lives
32 14C and
224 14N atoms
after 16,800
years or
3 half-lives
Half-lives
16 14C and
240 14N atoms
after 22,400
years or
4 half-lives
Half-lives
8 14C and
248 14N atoms
after 28,000
years or
5 half-lives
Half-lives
4 14C and
252 14N atoms
after 33,600
years or
6 half-lives
Half-lives
2 14C and
254 14N atoms
after 39,200
years or
7 half-lives
Carbon-14
 14C
is used to date organic samples like
wood, hair, shells (CaCO3) and other
plant and animal products
 Atmospheric 14C is incorporated into
organic molecules by plants during
photosynthesis
 Animals that eat the plants get 14C from
the plants they eat
 The current ratio of 14C to 12C in the
atmosphere is immeasurably small
Carbon-14
 With
a relatively short half life and an
earth billions of years old, all C14 should
be gone
 This would be true if not for production of
new 14C in the atmosphere as a result of
interactions between the upper
atmosphere and neutrons in cosmic
radiation
 The atmospheric ratio of 14C to 12C
represents an equilibrium between
14
Carbon-14
Sometime in the Ancient Past
Plant absorbs both
C12 and C14 in the
ratio they exist in
the atmosphere
CO2 fixation
Carbon-14
A Plant Grows Absorbing CO2
Carbon-14
The Plant Dies
Carbon-14
It Is Buried
Carbon-14
Over Time 14C Decays to 14N
Carbon-14
Over Time 14C Decays to 14N
Other Isotopic Dating Methods
 14C dating
is not useful for dating
geological strata so other methods have
been developed using isotopes with
much longer half lives
 Isotope
Examples include:
Product Half life
Method
Potassium-40
Argon-40
1.4 x 109
e- capture
Uranium-238
Lead-206
4.5 x 109
a emission
Uranium-235
Lead-207
0.7 x 109
Rubidium-87 Strontium-87
48.6 x 109
Thorium-232
14.0 x 109
Lead-208
Just How Old is Earth
By modern estimates – about 4.5 billion
years old
 How can we tell
 Remember Science 10 – Geology
 Radiometric dating is used to measure
the RADIOACTIVE DECAY of elements
 For example…

Is Spontaneous Generation of
Microbial Life Possible?

Aristotle (384-322 BC) proposed spontaneous generation
 living things can arise from nonliving matter

Leeuwenhoek presented data that seemed to support it

Spallanzani’s gravy experiments refuted it

Francesco Redi’s ‘s experiments with covered jars refuted
it
Redi’s Experiments
Spallanzani’s Gravy Experiment
Spallanzani’s Experiments


Concluded that

Microorganisms exist in air and can
contaminate experiments

Spontaneous generation of microorganisms
does not occur
Critics said sealed vials did not allow
enough air for organisms to survive and that
prolonged heating destroyed “life force”
Pasteur’s Experiments
Early Earth and the First
Signs of Life
Some things to consider…

Earth was formed ~4,500,000,000 yrs ago

For a few hundred million years Earth was very
hot and constantly bombarded from space

At this point there was no liquid water, life was
impossible
About 3,900,000,000 yrs ago, Earth was
solidified enough and cool enough for liquid
water
 Life apparently arose shortly thereafter

More points to ponder…

What was Earth like 3.9 billion years
ago?

Are there still places on Earth that
resemble these conditions?
How could life originally arise from nonliving matter?
 What did it take to form the first life?
 What is “life” anyway?

What was earth like 3.9 bya?


Earth was very different
Essentially no
atmospheric O2


Highly corrosive,
destroys molecules
Highly energetic


Lightning, volcanic
activity, UV radiation high
Provide energy for
chemical reactions
http://www.space.com/scienceastronomy/planetearth/earth_archaean_010716.html
How could life originally arise
from non-living matter?
The following hypothesis has been proposed:
1.
Non-living synthesis of small organic
molecules like amino acids and nucleotides
 Plenty of energy available
2.
Joining of small molecules
 Proteins and nucleic acids
The Urey-Miller
experiment:
Abiotic synthesis
of organics
Urey-Miller

Simulated early Earth
 Atomsphere
 H2O, H2, CH4, NH3
 Simple inorganic molecules
 Electric sparks (lightning)

Produced amino acids and other organic molecules
Couldn’t happen under modern conditions
 Oxidizing atmosphere attacks organic bonds
Or: possibly Earth was contaminated with organics from
space


Figure 26.10x Lightning
Self Assembly
Liposomes can “grow” by engulfing smaller
liposomes or “reproduce” by splitting off
Fig. 26.12a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Where did life originate?
Shallow water or moist sediments.
 Deep-sea vents


These sites have energy, produce some
organic compounds, and have inorganic
iron and nickel sulfides that can catalyze
some organic reactions
Deep sea
vents
Where are they now?
Early life on earth… 3 billion years
of microbes

Bacteria were the only life for billions of years

Atmospheric O2 was first made by cyanobacteria


Microbes still account for ~half of O2 produced globally
Plants and animals have only been here for ~600
million years


Australopithicus 4 million yrs
Homo sapiens 0.5 million yrs
Early Earth -- volcanic activity and
photosynthetic bacteria in dense mats
Key events in
evolutionary history
Evolutionary clock: Prokaryotes
Prokaryotes were the first
organisms on earth
3.5 billion yr old bacterial fossils Modern filamentous bacteria
Cyanobacteria – Very Old
Bacterial mats and Stromatolites
Fig. 26.4
Stromatolites in Northern Canada
Atmospheric oxygen began
accumulating 2.7 billion years ago

Photosynthesis probably
evolved very early in
bacterial history

Cyanobacteria, split water
and produce O2 evolved
over 2.7 billion years ago

This early oxygen initially
reacted with dissolved iron
to form the precipitate iron
oxide.

Seen today in banded iron
formations.
Banded iron formations -- evidence of oxygenreleasing photosynthesis
Oxygen accumulation

“Corrosive” O2 had an enormous impact on life,
dooming many bacterial groups

Some species survived in habitats that remained anaerobic
(these are “obligate anaerobes”)

Other species evolved mechanisms to use O2 in
cellular respiration, which uses oxygen to help harvest
the energy stored in organic molecules

Thus, prokaryotes altered the planet through O2
evolution, making aerobic respiration possible and
paving the way for other forms of life (eukaryotes)
Evolutionary clock: Eukaryotes
Evolutionary clock: Multicellular eukaryotes
Evolutionary clock: Animals
Unnumbered Figure (page 515) Evolutionary clock: Land plants