The History of Life on Earth Chapter 25

Brief History Earth is approximately 4.6 billion years old The first organic molecules (simple carbs, amino acids, etc) probably appeared around 4 billion years ago (bya) The first fossils of prokaryotes appeared about 3.5 bya The first fossils of eukaryotes appeared about 2.1 bya Question: How do you go from simple amino acids to a whole living organism in only 500 million years??

Conditions of Early Earth 4.6 bya Earth forms (Big Bang) Bombarded with huge chunks of rock and ice left over from the formation of the solar system; collisions generate heat which vaporizes and water that would exist 3.9 bya collisions stop Water vapor increases Volcanoes erupt releasing N2, CO2, CH4, NH3, H2, H2S Earth cools and water vapor condenses forming oceans Energy from lightning and UV radiation could have allowed organic compounds to form such as simple carbs, amino acids, and nucleotides

Miller and Urey (1953) Did an experiment recreating the conditions of early Earth in a lab setting Demonstrated the abiotic synthesis of organic molecules was possible Found that a variety of amino acids, simple carbs, and possibly nucleotides had formed

Key to Life The key to a living organism is that is can replicate itself and it has a metabolism How do you go from amino acids to a cell? Somehow amino acids must have linked together to form early proteins which could act as catalysts for a variety of reactions such as DNA/RNA replication and metabolism Protobionts are collections of abiotically produced molecules surrounded by a membrane-like structure of lipids They can reproduce on their own by pinching off parts of its membrane to form a new protobiont molecule They can also do simple metabolism IF RNA were to enter into a protobiont you could have the first living cell

25.2 Fossil Record Documents the History of Life Fossils are dated through radiometric dating based on the decay of radioactive isotopes Ex) living organisms contain C12 and C14. C12 will not decay even after death but C14 decays into N14 and it takes 5,730 years for half of the C14 to decay into N14 (called half-life). By measuring the ratio of C12 to C14 you can determine the age of a fossil Only works on organic (once-living) organisms Can only date fossils up to 75,000 year old For older fossils it is a ballpark age after comparing the ages of the rock layers the fossil was found between Electron antineutrino

25.3 Brief Tour of Life 3.5 bya – fossilized stromatolites; fairly complex so life must have started earlier 2.7 bya – evidence of photosynthetic bacteria; iron banding 2.1 bya – evidence of eukaryotic organisms; endosymbiosis 1.2 bya – evidence of multicellular algae 565 mya – evidence of more complex multicellular eukaryotic organisms 535 mya – Cambrian explosion; cnidaria, porifera, mollusks, soft bodied larger organisms 500 mya – colonization of land; larger fungi, plants, and animals

25.4 Continental Drift, Mass Extinctions, and Adaptive Radiation Continental drift served as a means of allopatric speciation Pangaea, Laurasia & Gondwana , present Mass extinctions occurred due to environmental changes as continents relocated Allowed for new niches to open up New niches open the door for adaptive radiation

Adaptive Radiation The evolutionary pattern characterized by a rapid increase in the number of kinds of closely related species Results in an evolutionary explosion of new species from a common ancestor Can occur when an organism invades a previously uninhabited environment (ie – Galápagos Islands) and has no competition or when a species has an adaptation enabling it to fill the niche of an extinct species Ex) The adaptive radiation of mammals following the mass extinction of the dinosaurs at the end of the Cretaceous period 65 million years ago. Mammals coexisted with the dinosaurs but were small, nocturnal insect eaters. The extinction of the dinosaurs left environments full of opportunities for other types of animals. More than 4,000 mammal species evolved within 10 million years, including whales, bats, rodents, and primates.