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Reconstructing Evolution

Part I: Pre-biotic evolution

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Overview

13.7 BYA Origin of universe

4.6 BYA Formation of earth

3.5 BYA First (prokaryotic) cell0.530 BYA Multicellular explosion

200-65 MYA Age of Dinosaurs

1.5 MYA First humans (Homo sp.)

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How do we know what we know?

Spectral analysis of galaxies.

Radioactive isotope dating of rocks.

Lab simulations.Inorganic geochemical record

Fossil record.

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Origin of Universe = 13.7 BYA

Putting Life on Earth in context

In 1920s Hubble discovered there aregalaxies outside our Milky Way.

Our Milky Way, an ordinary galaxy,contains about 100 billion stars.

Our sun is about 1/2 out along a spiral arm.

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Andromeda, our sister galaxy, is

2.5 million light-years away

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Billions and billions

In 1920-50, Hubble cataloged hundreds of

galaxies.

Last year, the Hubble Space Telescope counted

over 1500 galaxies in a 1/25-degree sliver of sky.

HSTs 1987 estimate was 50 billion galaxies in

the visible universe; current HST estimate is

hundreds of billions! (500 billion?)

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The Universe is Expanding

Hubble discovered that all galaxies are

moving away from us. How did he know?

The colors of visible light make the familiarrainbow of Roy G. Biv.

Red light has a longer wavelength than

blue. Moving away stretches light,making it appear redder (= red shift)

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Red shift

Spectral lines in the light from stars reveals

that elements like H and He are in the stars.

The wavelengths of the lines are precise.Analysis of light from galaxies shows that

the standard spectral lines are red shifted

to longer than expected wavelengths.

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Red shift (2)

Red shift indicates the object is moving

away from the observer.

Compare sound waves from a passing caror train whistle as heard by a roadside

listener.

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Age of the Universe

Measuring the rate of expansion enables us

to calculate backwards in time to when the

universe began, the Big Bang.

A Brief History of Time by Stephen

Hawkings describes subatomic events

milliseconds after the Big Bang.

Will expansion continue forever?

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Formation of sun = 5 Billion YA

Based on life cycles of stars.

Our sun is middle-aged

Fusion of hydrogen to helium releasesenergy like a hydrogen bomb

When hydrogen used up, sun will collapse

into white dwarf, about 6 BY from now.

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Age of the Earth

Cant be measured directly because all

surface rocks formed relatively recently;

the original surface rocks have been eroded

away, replaced, or covered by lava.

Can determine age of solar system (and so

Earth) by aging moon rocks & meteorites.

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Radioisotope dating

Radioactive isotopes like Uranium-238

decay into Lead-207 very slowly.

Half-life= length of time needed forhalfof the radio isotope present to decay.

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Radio isotope dating (2)

Highly accurate clock; ratio => age.

Half-life is constant. It is a property of the

nucleus of the atom and so is not affectedby the environment -- not pressure, not

temperature, not chemical reactions.

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Radio isotope dating (3)

Zircon crystals, when formed inside

volcanoes, take up uranium but notlead.

When analyze zircon crystals, the ratio of

Uranium (U-238) to Lead (Pb-207)

indicates how long ago zircon was formed.

For example, if ratio of U:Pb is 50:50, the

rock of 4.5 BY old; if 25:75 its 9 BY old.

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Radio isotope dating (4)

Other radioactive elements have different

half-lives with different useful ranges.

Potassium 40 is 1.3 BY, useful to 100 MY.Uranium-235 is 704 MY with a useful

range up to 100 million years.

Carbon-14 = 5730 Y, useful 0-60,000 years.

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How did first cell arise?

Many hypotheses, many missing links --

trying to piece together a story.

Laboratory simulations of ancientatmosphere show organic molecules like

amino acids can form spontaneously

Miller-Urey chamber: CH4, NH

3, H

2O, H

2

plus heat and spark (lightning)

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Origin of cell membranes

One hypothesis is based on lab observation

that cell-like microspheres can be formed

by cooling solutions of protenoids --

polypeptides created abiotically from amino

acids polymerized on hot surfaces.

These grow and divide spontaneously.

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RNA = first genetic material

Short segments of RNA (8-12 nucleotides

long) form spontaneously on clay (mudflat).

RNA can splice and reunite itself, withoutenzymes present.

RNA (mRNA, tRNA, ribosomes) can make

proteins (enzymes).

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Origin of DNA

RNA can make DNA if the enzyme

reverse transcriptase is present.

RNA might have first made reversetranscriptase, then made DNA.

HIV virus enters human cells as RNA, then

uses reverse transcriptase to make DNA.

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First Prokaryotic Cells

3.5 BY old fossils of bacteria and

cyanobacteria, in shape of tiny filaments,

found in Australia.

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Many Gaps

Currently, there are MANY gaps in our

understanding of the origin of the first cell.

God of Thunder? Thunder is producedwhen lightning heats air, causing a rapid

expansion of air, producing a sound wave.

God of the gaps as a basis of faith.

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Reconstructing Evolution

End of Part I