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

2. 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

3. 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)

4. 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

5. 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)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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