Origins of Life, Evolution and Earth's Biodiversity

Composition of living matter

Living matter is composed mainly of water and carbon (about 98% in the original estimate). It also contains elements such as iron, selenium, sulfur and potassium.

Autotrophs and heterotrophs

Autotroph: an organism that produces organic matter from inorganic matter (minerals, water and other substances) using solar energy.

Heterotrophic organism: an organism that feeds on organic matter produced by autotrophs.

Chemosynthesis and energy

Chemosynthetic organisms obtain energy from chemical reactions with other elements; these reactions may also yield oxygen or other products depending on the chemistry.

Origins of carbon and water

Carbon originates from inside the Earth, where it accumulated when the planet was formed. The water likely came from asteroids: in the early Solar System water could not condense in orbits near the Sun because temperatures were very high, so delivery from extraterrestrial bodies is a plausible source.

Early environment and the origin of life

Life is thought to have arisen in an environment shaped by intense submarine volcanism. With a dense atmosphere lacking free oxygen, life began in the sea, which provided protection for early organisms.

Hypotheses for the origin of life

Metabolic hypothesis

The metabolic hypothesis proposes that simple small molecules became isolated from the surrounding medium by membranes, initiating a series of complex chemical processes until a functional living unit emerged.

RNA world hypothesis

The RNA world hypothesis suggests that random RNA molecules emerged that were able to replicate; through mutation these molecules began a chain of evolution.

Biodiversity and the fossil record

There are an estimated 30–50 million species on Earth, of which about 2 million have been cataloged.

Fossils preserve the hard parts of plants and animals (bones, shells) or petrified remains of organisms.

Biology and evidence for evolution

Biology: examples include the structure of bones and vestigial organs (body parts that have no apparent function).

A key piece of evidence for common descent is that all living organisms use the same information transmission system: DNA.

Paleontological evidence

Paleontological evidence: about 300,000 distinct fossil species have been described. By 2000 we knew millions of living species overall; fossils represent only a small fraction of total species—roughly 1 in 7,000 species.

Molecular evidence

Molecular evidence: comparisons of DNA sequences provide strong support for relationships among organisms.

What is a species?

A species is defined as the set of organisms capable of reproducing with each other and producing fertile offspring.

Mechanisms of evolutionary change

Darwin and natural selection

Darwin proposed that advantageous characters are preserved while others are lost: individuals better adapted to their environment are more likely to survive and reproduce, transmitting those traits to offspring.

Lamarck and acquired traits

Lamarck proposed that species change by acquiring new traits to meet new needs; this idea contrasts with Darwinian natural selection.

Artificial selection

Artificial selection: humans select plants and animals with favorable characteristics and breed them to emphasize those traits.

Mass extinctions and modern hypotheses

One recent hypothesis attributes some mass extinctions to anoxia (lack of oxygen in the water) caused by atmospheric warming.

Geological eras and major events

• Paleozoic Era: ~650 Ma — Cambrian, Ordovician (extinction), Silurian, Devonian (extinction), Carboniferous, Permian (extinction). Ends ~250 Ma.
• Mesozoic Era: began ~250 Ma — Triassic (extinction), Jurassic, Cretaceous (~75 Ma).
• Cenozoic Era: ~75 Ma — Tertiary (~4 Ma noted in the original text).

About 65 Ma ago the non-avian dinosaurs became extinct, associated with the collision of an asteroid.

Human evolution

The origin of the human lineage is estimated at about 8 Ma in the original text. Major hominin taxa mentioned:

• First Australopithecus.
• Homo habilis.
• Homo ergaster (noted as ~1.8–1.2 Ma).
• Homo erectus.
• Finally, Homo sapiens and Homo neanderthalensis.

Note: All original factual points and figures from the source text have been retained and corrected for spelling, grammar and clarity while preserving the original content.