LIFE ON EARTH

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Life On Earth

Early Earth and the formation of organic molecules

Early earth contained no ozone layer = large amounts of UV radiation reached the earth

no ozone layer because there was little to no free oxygen.

volcanic emissions filled atmosphere = second atmosphere consisted of methane, amonia, hydrogen, carbon dioxide, carbon monoxide and small amounts of water vapor.

violent electrical storms and acidic rain formed the present warm and mineral rich oceans

only 2 possible ways molecules could have formed = on earth from simpler molecules or arriving from the cosmos

Implications of the existence of organic molecules in the cosmos for the origin of life on Earth

organic molecules have been found in inerstellar dust.

experiment where chemicals were exposed to UV radiation

result = production of many complex organic compunds. This suggests that the conditions in interstellar ices could be the site of the production of the organic chemicals necessary for the origin of life.

Spontaneous Generation:

For many generations it was believed that life spontaneously arose out of different materials. E.g. garbage turned into rats, rotting meat turned into maggots.

Significance: This theory is significant in understanding the origin of life, because it is untrue. We can further our understanding by learning from these errors. In 1862, Louis Pasteur carried out an experiment by using a flask containing boiled broth and showed that there was no spontaneous generation if contamination of the flask was prevented.

Chemicals for life formed on Earth (Abiotic synthesis in the Atmosphere and Oceans)

Haldane and Oparin suggested that Earth had all the necessary basic chemical components for life on Earth. They proposed that the early atmosphere on Earth contained little oxygen, and that the complex organic molecules could have been created from UV radiation, electrical discharges, and heat.

Urey & Miller Experiment

Urey and Miller set up a simulation of primitive earth. A mixture of hydrogen, ammonia, and methane in the form of steam was continuously electrically discharged for a week. The experiment resulted in a solution containing a number of amino acids and hydroxy acids which are vital components for living things. Urey and Miller’s experiment supported Oparin and Haldane’s theories on the origin of life, which showed that organic material, could be formed by raw materials.

Reason for experiment

To test the hypothesis of Oparin and Haldane which stated that conditions on the primitive Earth favoured chemical reactions that synthesized organic compounds from inorganic compounds.

It proved that living matter can be produced from non-living matter, and this chemosynthetic origin of life is believed by most biologists today.

Technologies that help us understand

Technology

Assistance in understanding

Deep sea equipment

Exploration of remote environments

Infra red observations

Gather and explore evidence from space

Aircrafts

Can pick up space dusts

Radioactive isotopes

Can date fossils

Electron microscopes

Can see greater details than lens or light microscope

Major stages of evolution of living things

4 bya – Organic molecules – amino acids, proteins, carbon compounds, etc

4-3.5 bya – Membranes – made of lipids and proteins

3.5-2.5 bya – Procaryotic heterotrophic cells – cells without membrane-bound organelles, obtained energy from organic molecules that existed in the primitive environment

2.5-2 bya – Procaryotic autotrophic cells – cells without membrane-bound organelles, obtained energy by making their own compounds (food)

1.5 bya – Eucaryotic cells – These cells have membrane bound organelles

1.5 bya – Colonial Organisms – Individual cells start to work together (not as 1 organism)

1-0.5 bya – Multicellular Organisms - Specialised cells which are dependant on each other in the colony (as one organism)

Evidence that suggests when life originated on Earth

Geological Evidence:

Banded iron formations in rocks –rings/ layers of rusted iron

Fe (II) ions + O2 ions (from photosynthesis)  Fe3O4 (sinks to sea floor)

Proves that oxygen was present in the oceans, therefore oxygen is present at the time when the layers are red

Oxygen cant escape into the atmosphere until all the iron in the water has been rusted and sunk to the bottom

Can be found between 4 and 2 bya (mostly)

Red Beds – iron rich rocks that are terrestrial (formed on land) and generally age 2 bya (no older)

They prove that oxygen was present in the atmosphere at that time

Palaeontological Evidence:

Schopf claimed to find fossils dating back to 3.5 bya

used 3D X rays to prove that it wasn’t just a flaw in the rock

Cyanobacteria and heterotrophic bacteria found from at least 850 mya

Stromatalites (colonial bacteria) – formed by cyanobacteria

Anoxic to Oxic atmosphere

As oxygen levels rose, photosynthetic organisms became more abundant, while the anaerobic organisms were inhibited due to the presence of oxygen.

The formation of the ozone layer protects the Earth from UV radiation

Explosion of diverse forms of plants and animals

The evolution of photosynthesis and respiration

Conflicts with different cultures

Different cultures and religious in the world have their own ideas about life, it maybe quite different to the scientific evidence.

In biblical creationism different organisms were made for specialised environments at the same time, the organisms that were created have not changed nor are they related

Australian Aborigines believe that ancestral beings created the world a long time ago in a period known as the dream time. The scientific theories in this area are different to what the aborigines believe and this can often cause conflict.

This conflict does however provoke people to think about what might have really happened and to question beliefs and leads to the formation of new theories

Impact of increased understanding of the fossil record on the development of ideas about the history of life on Earth

important because determines the information available to scientists

the more fossils found the more ideas can be developed about the evolution of life on earth

It was initially thought that Earth was 10 000 years old because someone calculated the years in the bible; this was proved wrong when a fossil was found and dated back to 3.5 bya.

Fossils have helped us to realise how complex organisms all came from simpler organisms

Further developments in our knowledge of present-day organisms and the discovery of new organisms allows for better understanding of the origins of life and the processes involved in the evolution of living things

Microscopes have allowed us to better understand the small parts of cells, and development of specific biochemical information, and sequence of the amino acids

Biochemical techniques has also helped us to study the pathways and shows differences in Eubacteria (splits growth into Archaea and other Eubacteria)

Organisms and their environment and role in it

Procaryotic Cell

Environment

Role in ecosystem

Archaea

Hostile environments

Carry out inorganic reactions for chemical energy

Eubacteria

All habitats, known for diseases many of them cause

Plays a vital role in the recycling in an ecosystem

Cyanobacteria

Mainly in marine environments

Carries out photosynthesis

Nitrogen – fixing bacteria

Live mutualistically on plants

Converts nitrogen to ammonium ions that can be converted to amino acids in the plants

Methanogens (Archaea)

Anaerobic conditions

Use hydrogen compounds and carbon dioxide to produce energy for themselves and release methane as a waste product

Thermophiles/ Thermoacidophiles (Archaea

Hot springs or at high temperatures in acidic environments

Carry out inorganic reactions for chemical energy

Halophiles

Very salty water (about 7x the concentration of sea water)

Carry out inorganic reactions for chemical energy

Deep – sea bacteria

Boiling undersea vents of volcanoes

Basis of food web, use sulphur compounds to derive energy

Cyanobacteria

Past environment

Today’s environment

Anaerobic – respiration without oxygen

Shallow seas (warm)

Anoxic

Becomes oxic due to photosynthesis

Warm, shallow salt water

Some live in slimy aquatic environments

Some are free living

Some live in other cells

Some in terrestrial environments

Flourish in warm, wet, damn conditions eg ponds

Some produce toxins i.e. we cannot swim in them

Evidence for this:

Current cyanobacteria can live in anaerobic environment

Cyanobacteria are oldest known fossil (found in Stromatalites)

Filamentous varieties found today living in aquatic environments

Role in ecosystem:

First reefs in aquatic life

Their photosynthesis led to oxygen in environment

Led to the evolution of plants

Nitrogen-fixing  change N2 into forms usable by other species eg. NH3 (ammonia), NO2 (nitrites) and NO3 (nitrates)

Binomial system

is the system that gives an organism its universal two-part name according to its genus and species.

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