Fossils and Earth’s History Notes CP Biology Ms. Morrison

The Fossil Record Provides evidence about history of life on Earth and how different organisms have changed over time 99% of all species have become extinct Is incomplete because not all organisms become fossils Fossils formed in sedimentary rock One of most important pieces of info = fossil’s age

Dating Fossils Two techniques for dating fossils Relative dating = estimating fossil’s age by comparing to other fossils (index fossils) Radioactive dating = calculate age of fossil based on amount of remaining radioactive isotopes in it (uses half-life)

Geologic Time Scale Precambrian Time - represents 88% of Earth’s history After Precambrian Time – scale divided into eras and periods 3 Eras Paleozoic (544 – 245 million years ago) – invertebrates and vertebrates Mesozoic (245 – 65 million years ago) – dinosaurs, mammals began evolving Cenozoic (65 million years ago – present) – Age of Mammals

Earth’s Early History Early atmosphere contained: hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water (toxic to life, no oxygen) Too hot to have liquid water (oceans)

Evolution of Early Life Miller and Urey – conduct experiments using gases found in early atmosphere, found that mixtures of organic compounds necessary for life could have arisen Precursor to cells = proteinoid microspheres – tiny bubbles formed from organic molecules Microfossils = microscopic fossils, single-celled prokaryotic organisms

Early Life Evolves Presence of photosynthetic bacteria – added oxygen to atmosphere Some life forms go extinct while others evolve to use oxygen for respiration Endosymbiotic theory – proposes that eukaryotic cells arose from living communities formed from prokaryotes Eventually sexual reproduction evolves which produces greater genetic variation and organisms become multicellular which allows for more diversity

Evolution of Multicellular Life Precambrian Time – rise of oxygen, eukaryotes, multicellular organisms, few fossils, life only in seas Paleozoic Era Cambrian Period – shells, outer skeletons, invertebrates (“Cambrian explosion”) Ordovician and Silurian Periods – 1st vertebrates, insects, 1st plants on land Devonian Period – Age of Fishes, amphibians on land Carboniferous and Permian Periods – life on the continents Era ends with mass extinction – 95% of all life in oceans disappeared, many fish and reptiles survived

Multicellular Life, pg 2 Mesozoic Era Triassic Period – Age of Reptiles, fish, insects, reptiles, cone-bearing plants, 1st dinosaurs and mammals appear Jurassic Period – dinosaurs become dominant, 1st birds appear Cretaceous Period – flying reptiles go extinct, leafy shrubs and small flowering plants appear Era ends with mass extinction – more than half plants and animal groups including dinosaurs wiped out

Multicellular Life, pg 3 Cenozoic Era - Age of Mammals Tertiary Period – climate warm and mild, marine animals and grasses evolved Quaternary Period – climate cooled, ice ages, human ancestors appeared

Patterns of Evolution Macroevolution = large scale evolutionary changes that take place over long periods of time Six patterns of macroevolution Mass extinctions: huge numbers of species die out together, often results in burst of new species appearing Adaptive radiation: single species or small group of species evolve into several different forms that live in different ways

Patterns of Evolution, pg 2 Six patterns of macroevolution, cont’d Convergent evolution: process by which unrelated organisms come to resemble one another (have analogous structures = similar structures that have different evolutionary histories) Coevolution: two species evolve in response to changes in each other over time, ex. Flowers and insects

Patterns of Evolution, pg 3 Six patterns of macroevolution, cont’d Punctuated equilibrium: pattern of long, stable periods interrupted by brief periods of more rapid change Different from graduation = slow, steady change over time Some biologists say new species produced by periods of rapid change Developmental genes: control how organism develops from embyro; homologous hox genes, activation of genes, and timing of genetic controls – all influence development of organism from embryo