Earth’s Early History and Evolution of Multicellular Life

What features can you see on Earth’s surface in the photograph and the drawing?

Formation of the Earth• Evidence shows that

the Earth is about 4.6 Billion years old

• Earth was not “born” in a single event, but over time (100 million years)

• Large amounts of heat melted the particles that made up the Early Earth

Formation of the Earth• The elements rearranged themselves

according to density

QUESTION: Where did the most dense elements go? Least dense?

Density DemoMaterial Density

Rubbing Alcohol .79

Lamp Oil .80Baby Oil .83

Vegetable Oil .92Ice Cube .92

Water 1.00Milk 1.03

Dawn Dish Soap 1.06

Light Corn Syrup 1.33

Maple Syrup 1.37Honey 1.42

Formation of the Earth

• The most dense elements formed the planet’s core

• The least dense elements (gases) formed the first atmosphere– Hydrogen– Nitrogen– (no oxygen…yet!)

Formation of the Earth• Early Earth’s atmosphere consisted of

hydrogen cyanide, carbon dioxide, carbon monoxyide, nitrogen, hydrogen sulfide, and water.

Formation of the Earth• Geologists infer that about 4 billion years ago,

Earth cooled enough to form rocks• Oceans did not exist because it was still too

hot! (evaporation)

Formation of the Earth• About 3.8 billion

years ago, the Earth’s surface cooled enough for water to remain liquid (condensation)

• Now oceans covered most of the Earth’s surface

First Organic Molecules• In the 1950s, chemists Miller and Urey tried to

simulate conditions on the early Earth in a lab

The First Organic Molecules• Over a few days, several

amino acids (building blocks for proteins) began to accumulate

• Miller and Urey’s experiment showed that mixtures of organic compounds necessary for life could have arisen from simpler compounds found on primitive Earth!

The Puzzle of Life’s Origin

• It took about 200-300 million years after the Earth cooled to find cells that looked similar to modern bacteria

QUESTION: How might these cells have originated?

The Puzzle of Life’s Origin

• Formation of Microspheres– Under certain conditions large organic molecules

can form tiny bubbles called proteinoid microspheres

The Puzzle of Life’s Origins

• Evolution of RNA and DNA– There is some evidence that RNA may have

existed before DNA– Small sequences of RNA could have formed and

replicated on their own

The RNA World Theory• The theory is catalytic RNA can self replicate

without enzymes and code for proteins. Scientists hypothesize that one of these proteins allowed RNA to convert into DNA.

Free Oxygen

• Microscopic fossils, or microfossils, of single-celled prokaryotic organisms have been found on rocks more than 3.5 billion years old

• They must have evolved in the absence of oxygen because Earth’s first atmosphere contained very little O2

Free Oxygen• Over time, photosynthetic bacteria became

common• Oxygen combined with iron in the oceans and

turned the oceans brown!• The iron oxide fell to the ocean floor, the

oceans became blue-green

Free Oxygen• Oxygen began to accumulate in

the atmosphere• Ozone formed- O3

• Created first “pollution” crisis!• The rise of oxygen in the atmosphere drove

some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration

Endosymbiotic Theory• Origin of Eukaryotic cells (cells with nuclei)• Eukaryotic cells arose from living communities

formed by prokaryotic organisms• Lynn Margulis– Mitochondria and Chloroplasts have similar DNA

to bacteria– Both have ribosomes– Reproduce by binary fission

Endosymbiotic Theory