Chapter 25: The History of life on Earth

change the course of biological evolution; conversely life changes the planet that it inhabits

that chemical and physical processes on early Earth produced very simple cells through a sequence of stages

Abiotic synthesis of small organic molecules Joining of these molecules into macromolecules Packaging of molecules into protocells Origin of self replicating molecules

along with the rest of the solar system; the first life evolved as early as billion years ago.

contained water vapor and many chemicals releases by volcanic eruptions Oparin and Haldane hypothesis earths early atmosphere was reducing (didn't have any oxygen, only nitrogen, hydrogen, sulfuric acid etc) and oceans were a solution of organic molecules

It showed that organic molecules (like amino acids ) could be produced from inorganic molecules but the existence of such an atmosphere on early Earth is unlikely

was from outer space carbon compounds found on meteorites

is not restricted to earth is becoming more accessible to scientific testing

polymerize when they are concentrated on hot sand, clay or rock

Replication and metabolism are key properties of life an may have appeared together in protocells Protocells may have formed from vesicles with a membrane like structure In water lipids and other organic molecules cam spontaneously form vesicles with a lipid bilayer Adding clay can increase the rate of vesicle formation Vesicles exhibit simple reproduction and metabolism and maintain internal chemical environment

was probably RNA not DNA

called ribozymes have been found to catalyze many differenct reactions including self splicing making complementary copies of short streteches of their own sequences or other short pieces of RNA

ONce

our oxidizing atmosphere is not conducive to the spontaneous formation of complex molecules

phylogenetic tree

1-1st cell 2- photosynthesis 3- aerobic respiration 4- eukaryotes 5- particularity 6- Cambrian explosion (535-525 million years ago) 7- Invasion of land

can be used to place major events in the earth's history in the context of the geological record

Hadean (origin of earth) Archaean (Oldest fossils of cells (prokaryotes) Appear) Proterozoic (Oldest fossils of eukaryotes appear) Phanerozoic:

Paleozoic- The Cambrian Explosion; first tetrapods and insects appear, Mesozoic- origins of mammals; dinosaurs evolved and radiate. (Amphibians, reptiles), Cenozoic- Humans appear; major radiation of pollution insects (Mammals and angiosperms)

rocks formed by the accumulation of sedimentary layers on bacterial mats

3.5 billions years ago

earth's sole inhabitants for more than 1.5 billion years

were essential to early life Have some aspects that possibly precede life itself

did not produce oxygen

probably evolved around 3.5 billion years ago in cyanobacteria (oxygen revolution)

it posed a challenge for life

date back 2.1 billion years

Proposed that mitochondria and plastids were formerly small prokayotrs living within larger host cells probably gained entry to the host cells as undigested prey or internal parasites

Inner membranes are similar to plasma membranes of prokaryotes Division and DNA structure is similar in these organelles and some proykaryotes Theses organelles transcribe and translate their own DNA Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

date the common ancestor of multicellular eukaryotes to 1.5 billion years

are of relatively small algae that lived about 1.2 billion years ago

until several hundred million years later Chinese paleontologists recently described 570 million year old fossils that are probably animal embryos

appear suddenly in the fossil record that was laid down the first 20 million years it the Cambrian period

provides a glimpse into he evolution of life on Earth. It shows that there have been remarkable changes in the kinds of organisms that have been abundant at different times

If an organism has a soft body, it is less likely to be fossilized; a hardshell is not crushed easily and does not decompose quickly

Organisms that live in an area with a low oxygen content are more likely to fossilize, organisms that live near a beach are more likely to fossilize; organisms that live in an area where sediments are actively being deposited are more likely to fossilize

are found in the deepest strata

allows us to indirectly date fossils up to billion of years old based on minerals in surrounding volcanic strata

evidence in the fossil record of large scaled extinction and or enormous radiation of many diverse new life forms defines the main boundaries of the geologic record

Began 4600 million years ago; the first prokaryotic cells and cyanobacteria appeared as well as the first animals

Began 542 million years ago; the first plants, jawless fish, bony fish. Amphibians became dominant vertebrate life form and the first reptiles and seed plants appeared . By the end many marine and terrestrial organisms became extinct.

251-65 million years ago ; reptiles radited out as dinosaurs to dominate the landscape, the first birds and mammals originated. flowering plants appeared and many organisms including most dinosaurs became extinct.

Followed the mesozoic and continues through modern times. Angiosperms evolved to dominate the landscape; primate groups evolved leading to the origin of apelike human ancestors and finally humans.

used water as an electron source from photosynthesis; oxygen began to accumulate in the atmosphere due to the action of photosynthetic cyanobacteria

the splitting of a single lineage into multiple species each adapted to a specific set of ecological demands

occurs when selective pressures produced by similar conditions (such as habitats) favor the evolution of similar solution

they provide positional information in the embryo