History The of Life
2/18/2008 4:21:00 PM
The problem with understanding the history of time We often have trouble differentiating 2 far off times (ex. 100 MYA and 1BYA) even thought very different things were happening at these times Tips for understanding the history of life Know the when and the what... Have a understanding of what the names refer to... o Animal? Mammal? Arthropod? Protist? Prokaryote? Know the BIG events... Keep an eye on the Tree...(next slide) Note: You should treat all dates here as approximations!
Age of Earth: 4.6 B.Y. Early Earth: 4.6-4.0 B.Y.A. Characterized by huge space impacts (meteors, etc.) Lots of volcanism The moon hit the earth during this time and started orbiting Earth became habitable - 4.0 B.Y.A. Water and primitive atmosphere Continents present but would be unrecognizable No free oxygen First forms of life 3.7 B.Y.A. Bacteria like organisms the first forms of life that we could see, there could have been other life that we just don't have evidence of Stramatolite fossils o Looks like a wavy rock or coral (when it is alive) because of a bacteria shield over the rock. o Keeps on growing until the bacteria on the inside mineralize and turn into rocks Scientists used to think life on other planets was impossible but the biologists not think that it is almost certain there is o Explored our own planet and have seen the diverse environments organisms live in. o Since we've been alive, hundreds of planets outside our solar system have been discovered Bacteria: the Prokaryotes: 3.7-2.0 B.Y.A. Bacteria are characterized by having a certain type of cell organization and biology which we call Prokaryotic. Refers to the biology of a cell. Dietary bacteria
o Our digestion is hinged on bacteria o No animal on our planet can get energy from plants. o Animals such as cows depend solely on the bacteria for digestion Biotechnology o Using bacteria for technology o Ex. Spraying bacteria after an oil spill o Waste product plants Nitrogen fixation o Most important organism on our planet. They change nitrogen into something we can use o No animal can use atmospheric nitrogen (N2) o Bacteria are stored in plant stems we get our nitrogen from the plants or from animals that eat those plants. o Lightning can also fix N2, but only about 10% of what is needed. Prokaryotes: single celled, very small, unique cell structure and DNA organization, many are killed by oxygen. Prokaryotes currently are the most numerous life form and have probably 10 times the biomass of Eukaryotes on Earth Buildup of free oxygen: 2.7-2.0 B.Y.A. Certain bacteria started to produce free oxygen as a byproduct of their metabolism (using sunlight) Significant levels of free oxygen had accumulated by 2.0 billion years ago. It was terrible for life on our planet because oxygen is so electronegative that it tries to pull the cells apart If there was free oxygen at the time when life started forming then it may not have formed Bacteria between 2.7 and 2.0 B.Y.A. had 3 evolutionary fates o Species would die o They could live in places where 02 couldn't penetrate o Some could evolve, change, and mutate to adapt to oxygen we are the product of these bacteria. Antioxidants were developed. Eukaryotes: 2.0 B.Y.A.-now The other type of cell organization which evolved from Prokaryotes Eukaryotes. These include all of the other life forms on our planet: every Plant, Animal, Fungi
Eukaryotes: Usually multicellular, small to very large, different and unique cell and DNA organization. Generally need oxygen to live Are usually bigger, even if they are single-celled How they are different from prokaryotes o Size o DNA organization + quantity (much more in Eukaryotes) o Double Membrane bound Organelles o New Organelles: Mitochondria + Chloroplast o Reliance on oxygen (most but not all) Early Eukaryotes o The first Eukaryotes were single celled, but larger and more complex than Prokaryotes. o We generally refer to the most primitive single celled Eukaryotes as Protists. o Protists are still around today, they are found in aquatic environments o Protists diversity and importance Animal like ingestion and movement Plant like uses sun for energy ex. Kelp (multi cellular) especially important to aquatic ecosystems o Fungus like mixture of 2 ex. Slime mold Multi-cellular creatures 1 B.Y.A. We know this because of fossils of very simple multi-cellular organisms What was the evolutionary sequence of single cell multi-cell o Primitive cells can get separated from each other then recombine to make organism again COLONIAL ORGANISM o Single cells don't need each other to stay alive o As they evolved, the cells became more dependant on each other until there is no way the cells can survive apart Still no plants or animals First Animals 650 M.Y.A. 1st animals are all pretty basic (probably like sponges) Even the basic animals were quite rare until 550 Why? Snowball Earth harsh conditions where most of the planets were covered with ice and snow. The levels of Oxygen also could have effected it Cambrian Explosion 550 M.Y.A. Explosion of animal diversity Ancestors to...
o Crabs and lobsters o Insects o Squid, octopus, and clams o Worms o Vertebrates (even humans) Fossil sites o Burgess Shale (Canadian Rockies) 525 M.Y.A. In the fossils we don't just see hard parts like shells, there are also soft parts like skin and organs o Chenjiang Biota (Hunan Province China) 545 M.Y.A. 20 million years before Burgess Shale Get to see changes that have occurred during this time Keys to the Cambrian Explosion o Cephaliazation development of the head o Segmentation the development of repeated segments to make up a body (vertebrate, ribs) o Bilateral Symmetry - specialization along the a long axis of animal the o Coelomization - Evolution of the Gut - digestion and energy usage o The general design of the body was experimented with and most, but not all (ex. Starfish), are built on this One of the most important fossils found in the Burgess Shale o A possible ancestor to all vertebrates: fish, amphibians, reptiles, birds and mammals o Pikia 550 M.Y.A. first time there is support on the inside instead of the outside o Similar to the modern Lancelet Plants 550 M.Y.A. Another Group of Eukaryotes that diverge from plate like Protists, These did not specialize on movement or the consumption of other living organisms. They further evolved mechanisms to use sunlight as a source of energy from the photosynthetic protests The first plants were small and unremarkable, but they would evolve characteristics which make them one of the most important groups of living organisms Ordovician 450 M.Y.A. 1st Eukaryotes to successfully invade land--moss bryophytes o Small
o Can grow our, but not up o Only can grow in very moist environments such as the rainforest, margins of lake, springs, oceans st 1 Reefs 1st Fish (jawless) o Descendants of Pikia o Covered in thick, chunky, armor like scales o Lack jaws have mouth that just barely opens and closes o Squid with hard shell was a large predator (explains armor or fish) Early Devonian 400 M.Y.A. Age of Fish Trilobites go extinct Bryophytes have evolved into ferns plants that have some height because of hard woods stem. They still need to be in moist environment. Uriptorides marine scorpions 10-12 feet long can go on land Evolution of the jaw o Placederms armored, eel like, usually small fish: go extinct relatively quickly because of competition o Condrichthyes cartilage fish sharks, rays o Osteichthyes bony fish most fresh and salt water fish: tuna, salmon, trout, eel: most dominant Late Devonian 350 M.Y.A. carconthieicraphans lobe finned fish not that diverse or important but they actually survived to become coelacanth important because they probably gave rise to amphibians Acanthostega a fish with fingers transitional forms that were thought to be missing links 100% living in the water o lived in shallow water with lots of plants and rocks o limbs let them move around obstacles Early Carboniferous 325 M.Y.A. 1st amphibians Euyrops: 3-5 feet long looked like huge salamanders Why move onto land? No Competition with vertebrates Insects had been on land for 100 MY= untapped food resource Late carboniferous 300 M.Y.A. Amphibians were outrun by reptiles Reptiles could survive without much water because of two adaptations o Eggs
Amphibians eggs look like they don't have a shell, they dry out very quickly Reptiles eggs have a leathery or hard shell that resists drying out
o Skin Amphibians is wet/shiny Reptiles have a dry scaly skin that helps stop water loss so they can live in drier environments End of the carboniferous split into 3 groups reptile wars I o Anapsids Are all extinct except distant relatives, turtles o Synapsids Also almost all extinct except mammals 1st dominant Permian (290-248 M.Y.A.) reptile Dimetrodon Looks like a dinosaur Has sail on back for thermoregulation The sail helped them wake up and warm up so they had an advantage over all the others o Diapsids Lizards, crocodiles, snakes, dinosaurs End of Permian extinction 248 M.Y.A. 95% of all species go extinct 50% of all families Extinction hits: plants, insects, reptiles (amphibians and marine life especially) Why? o Don't know for sure o In Russia there was a huge volcanic event 1 KM deep Thousands of KM wide Can cause global cooling then global warming Acid rain changes is Ph of water and soil Global fires Triassic 225 M.Y.A. Reptile wars II The Dinapsids didn't win the war this time, the Synapsids do Dinosaurs 1 group that went on to dominate land for next 150 years New group of plants evolve
o Gymnosperms new dominant plant on land Dry seeds and conditions are okay Pines, furs, cycades, redwoods o Dinasaurs ate these gymnosperms Jurassic 150 M.Y.A. Dinosaurs land dwelling Diapsids Air dwelling diapsids Marine diapsids The sinapsids change from reptile like to mammal like from 225125 M.Y.A. o Mostly small, mouse/squirrel sized o Adaptations Become endothermic (warm-blooded) hair (keeps warmth in) Nocturnal dominant animal at night Cretaceous 75 M.Y.A. Flowering plants- angiosperms o Dominant plants still o Everything but firs or ferns o More effective way to spread gametes through insects usually Insect diversity also explodes o Use plants for food, shelter Animals still about the same Cretaceous/ Tertiary 65 M.Y.A. Huge crater going at speed hit cozumel o Burning fires o Earth quakes, tornados, tidal waves (11 on the rictor scale) Huge extinction of Diapsids 2 groups made it through o Birds related to cranes, storks o Mammals diversity really spread 10 M.Y.A. Climate generally warm and tropical with jungles and forests common planet of the apes Hominid Evolution 4 M.Y.A. Climate changes again to grasslands Trees and jungles decrease greatly Many species go extinct but some adapt o Baboons
o Lucy the missing link between apes and humans Real difference between humans and other animals intelligence First step was not a huge brain, but being able to stand upright Hands/fingers began to specialize Small motor skills evolved at around same time as speaking (mouth and motor skills connected) 2 M.Y.A. Multiple (6-12) species of upright primates existed All others were out competed by homosapiens Neanderthals - 25,000 Y.A. Closest relatives Larger brains not necessarily smarter May have had culture, religion They were extinct by 25,000 Y.A. 200,000-250,000 Y.A.- modern humans are on land