Early Evolution of Life

Life on Earth originated between 3.5 & 4.0 bya

Origin of earth

crust solidified

Oldest evidence of life - stromatolites

The first cells may have originated by chemical evolution on a young

Earth.

Based on protobiont evolution

Process:

abiotic synthesis & accumulation of small organic molecules

joining of monomers into polymers

formation of protobionts

origin of heredity

Abiotic synthesis of organic monomers is a testable hypothesis

Formation of monomers

Oparin’s Hypothesis

Miller’s Experiment

Abiotic synthesis of organic monomers is a testable hypothesis

Laboratory simulations of early Earth conditions have produced organic

polymers.

protenoids - definition

known that small organic molecules polymerize when they are concentrated on hot sand, rock, clay

Protobionts can form by self-assembly

Organic molecules synthesized in the lab have spontaneously assembled into a variety of droplets with some properties associated with life.

microspores

Protobionts can form by self-assembly

Organic molecules synthesized in the lab have spontaneously assembled into a variety of droplets with some properties associated with life.

liposomes

Protobionts can form by self-assembly

Organic molecules synthesized in the lab have spontaneously assembled into a variety of droplets with some properties associated with life.

coacervates

RNA was probably the first genetic material.

The first genes may have been abiotically produced RNA, whose base sequence served as a template for both alignment of amino acids and polypeptide synthesis & alignment of complementary nucleotide bases in a primitive form of self-replication.

RNA was probably the first genetic material.

Why genes?

RNA was probably the first genetic material.

how genes operated

RNA was probably the first genetic material.

polymers of RNA have been produced abiotically

RNA can act as catalysts

ribozymes

The origin of hereditary information made Darwinian evolution possible

Once genetic information became incorporated inside membrane-enclosed compartments, protobionts would have acquired heritability and the ability to evolve as units.

The origin of hereditary information made Darwinian evolution possible

Process

protobiont incorporates genetic information into the aggregates of molecules

selectively accumulates monomers from surroundings & uses enzymes programmed by genes to form polymers and carry out chemical reactions

grows, splits, distributes copies of genes to offspring

Even if one protobiont survived, its descendants would vary because of mutations (copying errors)

The origin of hereditary information made Darwinian evolution possible

Differential reproductive success of varying individuals led to accumulated refinements to primitive metabolism & inheritance.

Example - evolution of DNA from RNA

Debate abounds regarding origins

Was abiotic synthesis of organic molecules necessary first step?

Panspermia

Debate abounds regarding origins

Challenge to RNA world of evolution

self-replication of RNA difficult

some simple organic molecules are capable of self-replication - perhaps something similar preceded the gene

Debate abounds regarding origins

Site of evolution

shallow water vs. deep-sea vents

Debate abounds the origin of life abounds.

RNA as genetic material