Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 17

The solar system formed about 4.5 billion years ago, and life left evidence on earth by 700 million years after that. Conditions when life originated differed from today.
Life does not spontaneously generate. Comets and meteorites contain chemicals also in organisms.
Origin of life simulations combine simple chemicals that include the elements in organisms in the presence of energy. More complex biochemicals form.
Amino acids may have polymerized into peptides and nucleotides into nucleic acids on hot clay or mineral surfaces that served as templates and structural supports and supplied energy.
The "RNA world" refers to the idea that RNA was the initial informational molecule of life. Reverse transcriptase could have copied RNA's information into more permanent DNA. RNA is the only biochemical that can carry genetic information and function as an enzyme, two properties important in the origin of life.
Phospholipids growing on supports and forming bubbles around nearby chemicals may have formed biological membranes.
Metabolic pathways may have originated when cell precursors, called progenotes, mutated in ways that enabled them to use additional nutrients.
The geological time scale is divided into eras, periods, and epochs.
Fossils from more than 3.5 billion years ago are unknown, because conditions then were harsh. The earliest fossils are of prokaryotes; the oldest eukaryotic fossils, of algae, date from 1.9 billion years ago. Evidence of multicellularity dates to 1.2 billion years ago.
The Cambrian explosion introduced many species. Life began in the seas. Amphibian-like animals ventured onto land about 360 million years ago. By 300 million years ago, reptiles had appeared and then diverged, eventually evolving also into birds and mammals. Invertebrates, ferns, and forests flourished. The Paleozoic era ended with mass extinctions.
Dinosaurs prevailed throughout the Mesozoic era, when forests were largely cycads, ginkgos, and conifers. In the middle of the era, flowering plants became prevalent. When the dinosaurs died out 65 million years ago, resources opened up for mammals.
Replacement of marsupials and monotremes with placental mammals in South America during the Cenozoic era illustrates the great effects of geographic changes on life.
Aegyptopithecus and other primates preceded the hominoids, which were ancestral to apes and humans. Hominids were ancestral to humans only. Four million years ago several species of Australopithecus existed and were gradually replaced with Homo habilis and then Homo erectus. The Neanderthals and Cro-Magnons were Homo sapiens, as are modern humans.