ORIGIN AND HISTORY OF LIFE

Origin of Life

Darwin’s theory is based around the idea of a common ancestor that all living organisms can be traced back to.

This ancestor is called the Last Universal Common Ancestor or LUCA.

Origin of Life

Since Darwin, advances in chemistry, evolutionary biology, paleontology, microbiology and other fields of science, have helped develop new hypothesis about the origin of life.

There is now a body of scientific evidence that life began 3.5-4 billion years ago and developed in 4 stages.

Origin of Life

Stage 1- Organic Monomers Simple organic molecules evolved from inorganic

monomers. Ex: Amino Acids and Nucleotides Stage 2- Organic Polymers

Organic monomers joined to form polymers. Ex. DNA, RNA, and proteins

Stage 3- Protocells Polymers became enclosed by membranes to

form the first cell precursors. Stage 4- Living Cells

Protocells began self replicating and gained other cellular properties.

Stage 1- Monomers

The Oparin- Haldane hypotheis, also known as the “primordial soup hypothesis” proposed that the lack of oxygen in the atmosphere gave ammonia (NH3) and Methane (CH4) strong reducing capability. Therefore, the redox reactions in the early atmosphere could have powered the chemical evolution of organic monomers from inorganic molecules.

Stage 1- Monomers

In 2008 a group of scientist re-tested the Miller-Urey experiment and found a greater variety of organic materials than Miller reported.

The iron-world hypothesis, proposed by Gunter Wachterschauser, stated that thermal vents emitted all the elements necessary for organic monomers to synthesize.

Stage 1- Monomers

Some scientist believe that the early organic monomers could have been brought to Earth by comets and meteorites.

Stage 2- Polymers

The Iron-sulfur World Hypothesis Research has found that organic

monomers will react in the presence of iron-nickel sulfides found at thermal vents.

Stage 2- Polymers

Protein-First Hypothesis Sidney Fox found that amino acids will

polymerize in the presence of dry heat. He proposed that when amino acids floating in the ocean were exposed to the sun, they formed proteionoids, small polypeptides that have some catalytic activity.

Stage 2- Polymers

RNA- First Hypothesis This hypothesis suggests that only RNA

was needed to progress towards the first cell(s).

In a study by Cech and altman, they discovered RNA can act as both a substrate and an enzyme. Based on their findings and the fact that some viruses have RNA, it would seem that RNA could have carried out processes of life associated with DNA and proteins today.

Stage 3-Protcells

Protocells are precursors to true cells. The formation of an outer membrane

was essential to regulation and maintenance of cellular functions.

The plasma membranes of today’s cells are formed from a phospholipid bilayer. Early membranes were likely composed of fatty acids, which are smaller than phospholipids but still have a hydrophobic tail and hydrophilic head.

Stage 3- The protocell

When put in water, fatty acids will assemble into small spheres call micelles with heads pointing out and tails pointing in.

If conditions are right, then they can form a bilayer called a vesicle.

Stage 3- The protocell

The first cells would have evolved some way to obtain nutrients.

Because they were formed by thermal vents, it’s probable that they carried out chemosynthesis (the synthesis of organic molecules from inorganic molecules and nutrients) before they evolved the ability to break down organic materials.

Stage 4- Self- Replication In modern cells, DNA directs protein

synthesis and information flows from DNA to RNA to protein.

It is possible that this sequence developed in stages. RNA-first Hypothesis- RNA would have first

regulated protein synthesis until DNA could evolve

Protein- first hypothesis- proteins developed first and then once a membrane was evolved could DNA and RNA evolve.

History of Life

Relative Dating of Fossils Even before the theory of evolution,

scientist were trying to age the strata layer

Geologists used index fossils (fossils used to identify deposits made at the same time) to relatively date the age of the layer

Absolute Dating Rely on radiometric techniques to assign

actual dates to fossils. Most common technique is Carbon-14

dating. Carbon-14 is a rare isotope of carbon that

has a half life of 5,730 years Only accurate for fossils up to 100,000.

The Precambrian Time

The precambrian time comprises about 87% of the geologic timescale.

This is when life began.

The first modern cells were probably prokaryotes, appearing approximately 3.5 bya. The first identifiable fossils are complex

prokaryotes The oldest were discovered in west Australia

date back 3.46 bya.

The Precambrian Time

Eukaryotic Cells Arise Eukaryotes originated around 2.1 bya

once oxygen was added to the atmosphere.

The nucleus may have developed by an invagination of the plasma membrane.

The endosymbiotic theory states that a nucleated cell engulfed prokaryotes, which then became organelles.

Evidence to support this theory Present day mitochondria and

chloroplasts have relatively the same size range as bacteria.

Mitochondria and chloroplasts have their own DNA and make some proteins.

Mitochondria and cholorplasts divide by binary fission.

Outer membrane of mitochondria resemble eukaryotic cells and the inner resemble bacterial cells

Multicellularity Arises Multicellular protists fossils have been

found in Canada dating back to 1.4 BYA These gave rise to the invertebrates,

whose fossils date back to 630-545 mya.

The Paleozoic Era

The paleozoic era lasted about 300 million years.

There were 3 major mass extinctions during this time period. 57% of marine species Over 50% coastal species Over 50% of corals

The Paleozoic Era

The Cambrian Period (542 mya) Referred to as the Cambrian Explosion All of today’s animals can trace their

ancestry back to this time. Animals had a hard exoskeleton.

The Paleozoic Era

Life began to move onto land around 500 mya.

Algae started invading damp areas on land during the Ordovician period.

Insects entered the fossil records during the Carboniferous period.

Vertebrates descent began during the Orovician period with the jawless fishes.

The Mesozoic Era

Carboniferous Period 359-299 mya Permian Period 299-251 mya Triassic Period 251-199 mya Jurassic Period 199-145 mya Cretaceous 145-65 mya

The Mesozoic Era

Reptiles can be traced back to The permian period.

The average size of dinosaurs were about the size of a crow, although there were a few giant species.

At the end of the Cretaceous period, dinosaurs became extinct.