New species appear by speciation species disappear by


New species appear by speciation . Species disappear by extinction

Species come and go. Species last 1 million years on average. But it varies among groups

It is estimated that more than 99% of all species that ever lived on Earth, amounting to over 5
billion species, are not extinct

The ultimate fate of all Earth's species is extinction. For example, the average lifespan of a
mammal species is 4 million years
The Fabric of Life

The cell is the structural and functional unit of all living organisms

Prokaryotes are cells that do not have a true nucleus

Eukaryotes are cells that have a nucleus

Cells combine to form organs, organs combine to form individual multi-celled organisms
The condition for life

Growth: Metabolism is the suite of chemical reactions that life forms use to convert atoms and
energy into more cell material

Reproduction: cells carry information in the form of DNA molecules that is passed from one
generation to the next. Genetic material can mutate (a copy with errors), providing genetic
variations. Mutations produce chemical novelty

Life is a self-sustaining chemical system capable of incorporating novelty and undergoing
Darwinian evolution
Carbon-based life

Carbon (6 protons, 6 neutrons, 6 electrons), the most versatile chemical element , with diverse
molecular functions, provide the building block of life

Carbon has the ability to bond with other carbon atoms as well as many other elements, notably
hydrogen, oxygen, nitrogen, and sulfur

Organic material can form long chains of atoms, interlocked rings, and complex molecular
arrangements , the backbone of proteins and carbohydrates, of fat, oils, of DNA and RNA

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Organic matter

Possibly the most fundamental compositional distinction is that of organic and inorganic matter

Organic applies specifically to compounds consisting of carbon atoms bonded together by
covalent bonds

In addition organic implies that the compound is biotic in origin

A common characteristic of organic compounds is their tendency to occur in long chain-like
structures called polymers

Important biopolymers in the Earth system:
o
Proteins: chains of bonded amino acids
o
Nucleic acids : (ex: DNA) built of nucleotides
o
Carbohydrates: the basis for most food we eat, a carbon-hydrogen-oxygen compound
Molecular evolution

Although the details are still unknown, biogenesis must have proceeded in incremental steps,
each with added molecular and chemical complexity
1. First, pre-biotic molecules, the building blocks of cells, must come to existence
2. Molecules would have to be selected, concentrated, and organized into life's essential
structures: a membrane protected cell
3. Molecular functions should have included reproduction with passing of (sometimes
erroneous) information
4. Natural selection and molecular evolution is the ultimate step for the emergence of life
Building blocks of life

Anywhere carbon dioxide (CO2) and water (H2O) interact in the presence of a sustainable
energy source the building blocks of life form:
o
Lightning in the atmosphere
o
Volcanic activity near the seafloor boiling the ocean
o
Solar radiation in the molecular clouds of the solar nebula

Pre-biotic molecules were ubiquitous, raining from the sky and rising from the bottom of the
sea, Every year, tons of organic material rain on Earth's surface from outer space

Building blocks of life may presumably be found all around the