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Origin of the earth

Big bang happened 14 billion years ago.

Earth and Moon formed 4.5 billion years ago (4.5 X 10 )

Oldest rock is 3.9 billion years old• No rock on earth is as old

as the earth itself!

Oldest fossils are 3.8 billion years old

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2

Origin of the earth

The Sun and the planets are formed from a cloud of cosmic dust and gas.

As the earth condensed, a stratification of its components took place.

Heavier materials, moved into the center while lighter concentrated near the surface.

A crust formed, floating on the hot molten interior.

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The early atmosphere

It is thought to have been principally composed of:• N2• Co2• CO• H2O • H2

Also thought to have been present:• H2S• CH4

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The early atmosphere

The early atmosphere is said to be a reducing atmosphere • because it is thought to

have contained much hydrogen which easily donates electrons (reduction).

In a reducing environment it takes little energy to form carbon rich molecules.

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The early atmosphere

What gas is conspicuously absent in the early atmosphere?

When and by what means did this gas become 1/5 of today's atmosphere?

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The early oceans

The early oceans are thought to have been formed when the earth cooled and the gaseous H2O fell in torrential rains on the crust.

They must have had dissolved salts and minerals from the land around them and dissolved gasses from the atmosphere.

And soon organic materials were added.

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The Miller - Urey experiment

They tested a theory first put forward by the Russian Alexandr Oparin.

They tested whether it was possible to get organic compounds in an experiment that re-created the conditions around the early earth.

They succeeded in getting organic gasses and simple organic acids and amino acids in solution.

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The origin of life

Divide into 5 groups Each group explores

one possible theory on the origin of life• 1. Special/divine creation• 2. Spontaneous creation• 3. Panspermia, arrival of

material from outer space.

• 4. Primitive soup, abiotic replication of RNA.

• 5. Steady state.

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Clay as a catalyst

Aharon Katchalsky (worked in Israel) found that certain types of clay could catalyse the formation of polypeptides from amino acids.• This supported the ideas

that life did need something like a clay catalyst at the beginning because the oceans were too diluted.

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The Cairns-Smith´stheory (or clay creation)

First “organisms” were made of minerals.

Basic material is silica acid, Si(OH)4, in clay.• It easily polymerises• not uniform, can be

straight or branching (with occasional minerals Mg+2, Al+3, Fe+2)

• diverse infrastructure• crystal genes were

formed

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The hen or the egg?

“DNA makes RNA makes Protein”

What was the first molecule that could replicate itself?

Which of these three takes part in all the processes?

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The RNA world

Ribose is more easily synthesised than deoxyribose.

RNA can act as a catalyst.

RNA can catalyse a complimentary strand of itself.• a 52 nucleotide stretch of

RNA can replicate itself

but RNA is not stable.

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Coacervate droplets(the basis of the first cells?)

Small spherical bubbles made of a bi-layered membrane.

Capable of • absorbing substances from

the surrounding solution• facilitated chemical reactions• exporting products.

Grow by accumulating sub-unit molecules from surroundings.

Divide by pinching, form buds.

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Earliest cells

Fossils of Prokaryotes from around 3.8 billion years ago represent the earliest life forms known on earth.

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Endosymbiotic theory Lynn Margulis (USA)

prokaryotes have been incorporated into the eukaryotic cell.

This theory explains f.ex. why mitochondria and chloroplasts :• have a double membrane.• have their own DNA, a ring

like prokaryotes• have smaller ribosomes• have enzymes on their inner

membrane related to prokaryotic enzymes

• divide by splitting in two

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Endosymbiotic theory Lynn Margulis (USA)

This also means that it is from prokaryotes that the four eukaryotic kingdoms arise.

K. Fungi K. Plants K. Animals

K. Protists

K. Prokaryotes