The History of Life Chapter 12

The Fossil Record Fossil Forming Most fossils form in sedimentary rock Perminerilization Natural Casts Trace Fossils Amber preserved fossils Preserved remains Most fossils form in sedimentary rock Preminerilization – minerals carried by water are deposited around a solid structure – most common Natural Casts – flowing water removes all the original bone or tissue leaving an impression in the sediment Trace fossils- record the activity of an organism; nests, burrows, imprints, and footprints Amber preserved fossils – organisms trapped in tree resin Preserved remains – entire organism trapped in ice or volcanic ash or immersed in bogs Fossil Formation Must be buried or encased in some type of material (sand, deiment, mud, tar) very soon after death Groundwater trickles into tiny pores and spaced in plants and bone Excess mineral in the water are depostied on the remaining cells or tissues Many layers are deposited and left behind Resulting minerals are the same shape as the organism

The Fossil Record

The Fossil Record Relative Dating Estimates the time an organism was alive based upon it’s placement in rock layers Allows for inferences of species origin Does not provide actual age dating of fossil

The Fossil Record Radiometric Dating Half life Estimates actual or absolute age Calculation of the age of a sample based upon the amount of remaining radioactive isotopes Half life The amount of time it takes for half of the iostopes in a sample to decay into another element Different items have different half lives Isotopes are atoms with differing numbers of neutrons Carbon has three isotopes – C12, C13, and C14 – 98% are C12 Carbon 14 has a half life of 5730 years

The Fossil Record Carbon-14 Dating Good for recent remains Carbon-14-taken up by organisms while they are alive C-14 begins to break down when organism dies Researchers compare the amount of Carbon-14 to Carbon-12 or Nitrogen-14 The larger the ratio of C-14 to C-12 (or N-14), the older the organism Carbon has three isotopes – C12, C13, and C14 – 98% are C12 Carbon 14 has a half life of 5730 years – after 5730 years half the C14 in a fossil will be gone

The Geologic Time Scale Index Fossils Easily recognized and the species must have existed for a short period, but have a wide geographic range It will only be found in a few layers, but they will be specific and in different locations Trilobite

Geologic Time Scale Evolutionary time is represented by the Geologic Time Scale This orders rock by age Divided into units based on order rocks and fossils were formed Geologic Time Scale was developed by comparing index fossils throughout the world Eras Periods Epochs Time did not begin until the Precambrian period – covers about 88% of the Earth’s history

Geologic Time Scale Time between the Precambrian period and now is divided by eras Paleozoic Mesozoic Cenozoic These divisions are defined somewhat by the organisms present Paleozoic – 300 million years – life begins – ancient life Mesozoic – 180 million years – Dinosaurs – middle life Cenozoic – last 65 million years – age of mammals – recent life

Geologic Time Scale To further define time, eras are divided into periods The Cambrian period is important to biology due to the huge explosion of organisms Epochs Smallest unit of time; several million years

Origin of Life Earth is about 4.6 billion year old How did the earth get here? Formed by a condensing nebula Material pulled together Collisions caused the formation of planets

Origin of Life Earth was very hot, violent first 700 million years Many objects struck Earth releasing heat – kept Earth in a molten state Objects eventually separated into layers Hydrogen, carbon monoxide, water vapor, methane, and carbon dioxide released Oxygen not released until about 2 billion years ago

Origin of Life Miller-Urey Experiment Lightning strikes caused inorganic molecules to form organic molecules Electricity applied to these inorganic molecules led to the production of amino acids Miller and Urey simulated the chemical nature in a lab of early earth They filled a flask with hydrogen, methane, amonia and water to represent the atomosphere They also made sure no microorganisms were present in the system They then passed an electric spark to simulate lightining The results showed that several amino acids began to form over several days This suggested that the building blocks for life may have arisen from simpler compounds present on primitive earth

Origin of Life Meteorite Hypothesis Amino acids have been found in meteorites Suggests that amino acids could have been present when Earth formed

Origin of Life Iron Sulfide Hypothesis Iron sulfide from deep sea vents form chimneys Compartments in these chimneys acted as pockets for biological molecules The walls of these compartments acted as the first cell membranes

Origin of Life Lipid Membrane Hypothesis Lipids tend to form spheres – liposomes These spheres could enclose organic molecules Give rise to cells

Origin of Life RNA – Early Genetic Material Ribozymes – RNA molecules that can catalyze chemical reactions Can make enzymes that would cut itself, copy itself, and make more of itself Short chains of RNA can form from inorganic molecules

Early Single-Celled Organisms Early microbes changed the Earth Deposited minerals, gave off oxygen Cyanobacteria – bacteria that carry out photosynthesis Stromatolites – colonies of cyanobacteria Release of oxygen allowed for aerobic organisms If doing photosynthesis, then giving off oxygen

Early Single-Celled Organisms Early prokaryotes are considered the ancestors of eukaryotes Early on some smaller prokaryotes began to enter into other prokaryotes Endosymbiotic Theory Eukaryotic cells arose from living communities formed by prokaryotic cells These prokaryotes did not infect the host and the host did not ingest the ones that entered. The prokaryotes that entered began living in the other cells. This resulted in a symbiotic relationship (each one helping the other) One group could use oxygen to generate ATP – these became mitochondria Another groups carried out photosynthesis – these became chloroplasts in plants This idea came about when microscopes revealed that membranes of mitochondria resembled plasma membranes of free living prokaryotes

Eukaryotic Origins Evidence of the Endosymbiotic Theory Mitochondria and chloroplasts: Contain DNA similar to bacterial DNA Have ribosomes whose structure and size closely resemble bacterial ribosome Reproduce by binary fission These three key pieces of evidence are what give credence to the idea that eukaryotes formed from prokaryotes

Reproduction and Multicellularity After arrival, eukaryotes reproduced sexually This increased the speed of evolution Sexual reproduction allowed for shuffling of genes Offspring never resembled their parents exactly This increased the gene combinations – So? Sped up because prokaryotes reproduce asexually and divide simply into two cells which are identical to the initial cell By increasing the number of gene combinations, the probability that favorable combinations will be produced increases – This increases the chance of evolutionary change in a species due to natural selection

Early Single-Celled Organisms Sexual Reproduction vs. Asexual reproduction Asexual – ease, rate of reproduction, energy efficient Sexual – genetic diversity, increase in evolution

Paleozoic Era Fossil evidence shows a very diverse life during this era Was initially thought that much of this life originated during this era Actually came about much earlier

Cambrian Period Cambrian Explosion The explosion and diversification of life during this period Organisms had shells and outer skeletons Common organisms: Jellyfish, worms, sponges Brachiopods, trilobites

Ordovician and Silurian Periods Ancestors of modern octopi and squid appeared Arthropods became the first land animals Jawless fishes became the first vertebrates Plants evolved from aquatic ancestors

Devonian Period Plants began to adapt to drier areas This allowed for invasion of new habitats “Age of Fishes” Many groups of fishes present in the oceans Vertebrates began to also invade land Most fishes had jaws, bony skeletons, and scales on their bodies Sharks appeared late in this period When fish developed the ability to crawl, they moved to land. These evolved to the amphibians

Carbiniferous and Permian Period Reptiles evolved from amphibians Winged insects began to appear Dragonflies and cockroaches Plants became abundant and when they died, their remains are now coal At he end of this period there was a mass extinction. As much as 95% of the complex life in the oceans disappeared This extinction is believed to have resulted from increased concentrations of CO2 in the atmosphere from a comet strike or metorite

Mesozoic Era Lasted approximately 180 million years This era is marked by two main features Dinosaurs Flowering plants

Triassic Period Fishes, insects, reptiles, and cone-bearing plants were prominent “Age of the Reptiles” Coelophysis – meat eater Mammals first appeared – mouse or shrew style

Jurassic Period Dinosaurs the prominent life form Ruled the earth for about 150 million years Many scientists think that birds are close relatives

Cretaceous Period Dinosaurs still present New life came about: Leafy tress Shrubs Small flowering plants Another mass extinction brought this period to and end More than half the plant and animal groups wiped out Extinction brought on by another impact, but the extinction was not as thorough

Cenozoic Era About 65 million years ago Mammals evolved Could live on land, in water, and even the air Tertiary Period Warm and mild climate Whales and dolphins evolved Quaternary Period Climate cooled – ice ages Earth warmed up about 20,000 years ago Homo sapiens – 200,000 years ago in Africa

Extinction 99% of all species that ever existed are extinct Extinctions happen for reasons Resources Environments change Each extinction brings an opportunity for other species to succeed

Primate Evolution Common Ancestors Primates are mammals with flexible hands and feet Divided into two groups Prosimians Anthropoids

Primate Evolution Promisians Anthropoids Oldest primate group Active at night Lemurs, tarsiers Anthropoids Divided into old and new world monkeys as wells as hominoids Hominids can be even further divided Lesser apes (gibbons) Greater apes (gorillas) Hominids (humans) New world monkeys live in trees and are native to the Americas Old world monkeys most travel and forage on the ground – also have large brains

Primate Evolution Bipedalism Walking upright, on two legs Came before larger brains and tool manipulation Allowed to reach higher into trees, freed the hands

Primate Evolution Early Human Fossils Two important genus Homo habilis Australopithecus Homo habilis Homo neanderthalensis Neanderthals Homo sapiens Modern humans Homo habalis – handy man for the stone tools that he used-lived in Kenya and Tanzania-larger brain than that of Australapithecus Neanderthals were found in the Neanderthal valley of Germany-coexisted with Homo sapiens

Primate Evolution Human Evolution Modern humans came about 100,000 years ago Came out of Ethiopia Brain was key to evolution Enlarged skull and brain

Primate Evolution Australopithecus afarensis Homo erectus A. Afarensis is one of the better known early hominid species – lived 3-4 million years ago in Africa- brain about the size of a modern day monkey – human like limbs H. Neaderthalensis and H. sapiens coexisted – could have been competition for resources that forced extinction Homo neanderthalensis Homo sapiens