UNIT 3A ORIGINS OF LIFE

WHERE ARE WE IN THE UNIVERSE?

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WHAT HAPPENED FIRST - 4.6 BILLION YEARS AGO

1. The cosmic dust left over from the “Big Bang” helped form the Earth

–Big Bang Theory- the theory that the entire universe began condensed together and in an instant began to rapidly expand outward ~14 billion years ago.

The resulting “cosmic dust” or matter expanded, cooled, and with the help of gravity interacted to form the stars, galaxies, etc.

The early Earth was a land of molten rock and violent volcanic activity and its crust was not yet solidified.

4.2 BILLION YEARS AGO2. The Formation of the Oceans

As the earth was forming, gasses were released from the molten core in volcanic activity.

These gasses formed a cloud around the earth and were held as an atmosphere by the earth’s gravity.

As the earth cooled and the crust solidified, the vapor condensed to liquid water and the rain began to fall.

It rained such an enormous quantity over millions of years that the oceans of the world were formed.

4 BILLION YEARS AGO3. Primordial Soup

• Inorganic molecules in the water and atmosphere are believed to have reacted in the presence of the enormous amounts of energy on the planet to produce small organic molecules.

With the accumulation of the small organic compounds, the oceans became a “primordial soup” in which protocells (early, incomplete, primitive cells) formed.

Over time, these protocells accumulated more molecules and could function as unicellular organisms.

* RNA used before DNA- “RNA World”!

3. PRIMORDIAL SOUP (CONTINUED)Evidence for the creation of primordial soup:

• In 1953, Stanley Miller and Harold Urey did an experiment that showed that the inorganic molecules on primitive Earth could have combined to create organic molecules

Gases like CH4, NH3, H2O, & H2 were placed in the top chamber to represent gases in the atmosphere.

Water was placed in the lower left chamber and heated to represent the evaporation of ocean water.

Source of energy: electricity (to represent lightening) was used on the “atmosphere”

Substances “rained down” and were collected in a trap to be analyzed.

Substances (organic soup) collected: HCN (hydrogen cyanide), lactic acid, acetic acid, simple amino acids, formaldehyde.

organic soup, gasses,

lightning (electricity),

oceans, rainfall, heat source 

3. PRIMORDIAL SOUP (CONTINUED)From the primordial soup came protocells, then the first unicellular organisms.

3.5 BYA- The first cell (unicellular organism) came into being

The first cell/organism is believed to have been:

A. Unicellular- made of one cell, multicellularity had not yet evolved

B. Anaerobic- there was no oxygen gas yet on the planet

C. Heterotrophic- it is easier to eat something than create food internally (photosynthesis had not yet evolved)

D. Prokaryotic- no internal membranes and no nuclear envelope- these are complex structures that had not yet evolved.

2.5 BILLION YEARS AGO

4. The evolution of photosynthesizing organisms caused oxygen to enter the atmosphere.

Oxygen in the upper atmosphere formed ozone, which filtered UV light.

The presence of oxygen also meant that most environments were unsuitable for anaerobic prokaryotes.

Photosynthetic cyanobacteria and aerobic bacteria multiplied as new metabolic pathways evolved.

1.5-2 BILLION YEARS AGO

5. Endosymbiont Recruitment

Most likely the eukaryotic cell evolved from the prokaryotic cell, acquiring its organelles gradually.

Mitochondria and chloroplasts may once have been prokaryotes that started to live inside other cells (endosymbiosis)

1 BILLION YEARS AGO

6. Sexual Reproduction• It is not exactly known when

multicellularity began but the first multicelled creatures were likely microscopic.

Sexual reproduction would have its origins here and would have been an important first step toward the development of complex macroscopic organisms.

438 MILLION YEARS AGO

7. The first land organisms were plants!

Before this point all life existed in bodies of water.

The arrival of plants on land helped to form the soil, create habitats, further change the atmosphere, and create a food source.

This changed the surface of the Earth and made it livable for animals.

8. Reptiles & Mammals

The first reptiles appeared about 286 - 360 million years ago

The first dinosaurs and mammals appeared about 200 mya.

Placental mammals appeared about 100 mya.

175-225 MILLION YEARS AGO9. The Continental Drift Theory

• continents are part of the Earth’s crust that moves due to the fluid mantle layer below.

About 225 mya, the continents were joined to form one supercontinent called Pangea which then divided into two subcontinents.

This separated species and allowed for different environments and further speciation (evolution of one species into other species)

Continental driftexplains why some

coastlines are mirror images of each other

HUMANS AND OUR ANCESTORS

10. Monkey-like primates appeared about 30 mya.

The first hominids (the great ape family of primates) appeared 2 – 6 mya

Humans appeared about 2 mya.

Life on Earth

5 BYA 4 BYA 3 BYA 1 BYA2 BYA Present Day

500 MYA