Chapter 25

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Concept 25.1 Conditions on early Earth made origin of life possible

Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages

1. Abiotic Synthesis of small organic molecules (Creation from something not living)

2. Joining of these small molecules into macromolecules

3. Packaging of molecules into protocells (vesicle: structure surrounded by membrane)

4. origin of self-replicating molecules

Synthesis of organic compounds on early earth

Early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (No oxygen present in atmosphere)

1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible (a lot of amino acids formed under these conditions; experiment repeated in 2008 showing even more amino acid formation)

Abiotic synthesis of macromolecules

RNA monomers have been spontaneously produced from simple molecules

Small organic molecules polymerize when they're concentrated on hot sand, clay, or rock

Protocells

Replication and metabolism= key properties of life and may have appeared together

Fluid-filled vesicle with membrane life structure

In H2O, lipids can spontaneously form vesicles with a lipid bilayer due to hydrophobic and hydrophillic regions

Concept 25.2 Fossil record documents history of life

Fossil record biased in favor of species that existed for a long time, were abundant and widespread, and had hard parts

Dating of Fossils

Sedimentary strata reveals relative age

absolute age determined by radiometric dating

parent isotope decays to a daughter isotope at a constant rate

half life: time required for half of the parent isotope to decay

Radiometric dating is 60-75,000 years old: some sort of element contained in living molecules that begins to break down after death of that molecule into other elements, Measure amount of element left and base it off half life to determine absolute age

Origin of new groups of organisms

Mammals belong to tetrapod group

evolution of unique mammalian features can be traced through gradual changes over time (articular and quadrate bones used to be apart of the jaw hinge but have migrated into our ears)

Concept 25.3 Key events of lifes history

Geological record divided into Archaean, Protozoic, and Phanerozoic eons

Phanerozoic encompasses multicellular eurkaryotic life

Phanerozoic is divided into 3 eras: paleozoic, mesozoic, and cenozoic

First single-celled organisms

Oldest known fossils are stromatolites (first single celled organism, 3.5 billion years ago)

Prokaryotes= earths sole inhibitants (3.5-2.1 billion years ago, only living organism)

Oxygen still missing from atmosphere making these prokaryotes obligate anaerobes (obligated to be without oxygen, oxygen would poison them)

Photosynthesis and Oxygen revolution

2.7 billion years ago oxygen began accumilating atmosphere

Oxygen revolution: 2.7-2.3 billion years ago caused extinction of many prokaryotes (some survived and adapted)

The first eukaryotes

2.1 Billion years aho

include nuclear envelope, mitochondria, endoplasmic reticulum, and cytoskeleton

Endosymbiont theory: mitochondria and plastids originally small prokaryotes living within larger host cells

Endosymbiont= cell living inside host cell

gained entry to host cells as undigested prey

serial endosymbiosis= mitochondria evolved before plastids through sequence of endosymbiotic events

chloroplasts and mitochondria engulfed by eurkaryokes (phagocytosis)

Earliest multicellular eukaryotes

1.5 billion years ago

oldest known fossils are of small algae that lived 1.2 billion years ago

"snowball earth" hypothesis suggest periods of extreme glaciation caused life to retreat near equator or deep-sea vents (750-580 million years ago)

Cambrian Explosion

sudden appearance of fossils resembling modern animal phyla in cambrian period (235-525 million years ago)

provides first evidence of predator-prey interactions

DNA analysis suggest many animal phyla diverged before this (700 million-1 billion years ago)

Fossils in China support that Cambrian explosion had a very long fuse

Colonization of land (acquatic-terestrial)

500 million years ago

vascular tissue in plants transports materials internally and appeared 420 million years ago

countless numbers of symbiotic relationships between plants and animals overtimme

anthropods and tetrapods= most widespread and diverse land animals

tetrapods evolved from lobe-finned fishes around 365 million years ago

snakes are considered tetrapods who secondarily lost the trait of 4 limbs due to environmental adaptations

Concept 25.4 Rise and fall of groups of organisms reflect difference in speciation and extinction

Plate Tectonics

3 points in time earth had one big supercontinent (1.1 billion years ago, 600 mill. years ago, and 250 mill yrs. ago)

Consequences of continental drift: deepening of ocean basins, reduction in shallow water habitat, colder and drier climate inland, continents climate changes as they move north and south, separation of land masses can cause allopatric speciation

Mass Extinction

"Big Five" Events

Permian Extinction (separates paleozoic and mesozoic eras)

less than 5 million years ago

95% of marine animal species extinct

causes: intense volcanism, global warming, reduced temp. gradient, oceanic anoxia

Cretaceous Extinction (separates mesozoic and cenozoic)

65.5 million years ago

half of marine species and many terestrial plants and animals including most dinosaurs

Caused by meterorite that created Chicxulub crater off coast of mexico

Consequences of mass extinction

alters ecological communities and niches available

5-100 million years for diversity to recover

predator percentage in marine life increased

can pave way for adaptive radiation