Fossils an introduction
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Fossils: An Introduction. The Theory of Evolution by Natural Selection. Evolution is a theory (set of related, well-supported hypotheses) that explains the diversity of living organisms alive today and those that have lived before.

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Fossils: An Introduction

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Fossils: An Introduction


The Theory of Evolution by Natural Selection

  • Evolution is a theory (set of related, well-supported hypotheses) that explains the diversity of living organisms alive today and those that have lived before.

  • Natural selection is the mechanism by which that theory proposes species change over time, form new species, and sometimes go extinct.

  • The support for evolution by natural selection includes 2 major lines of physical evidence:

    • Earth’s fossil record

    • Genetics


Fossils

  • Fossils are the preserved remains or traces of ancient organisms.


Types of Fossils

  • Permineralization: the most common way fossils are made. Remains are covered by sediment and compressed and mineralized into rock.


Other Types of Fossils

  • Amber

  • Ice

  • Trace fossils

  • Many more…


A Taste of Geology

  • Fossils are found only in sedimentary rocks.

  • As soil and rocks are weathered, particles called sediment build up at the bottom of the water.

  • Increased pressure crushes the particles together, making sedimentary rocks


Law of Superposition

  • The oldest rocks are on the bottom of the column, the newest rocks are on top


Geological Time

  • Radioactive dating is used to measure rocks, and fossils found in them:

  • The mathematical expression that relates radioactive decay to geologic time, is:

    • D = D0 + N(eλt − 1) where

    • t is age of the sample, D is number of atoms of the daughter isotope in the sample, D0 is number of atoms of the daughter isotope in the original composition, N is number of atoms of the parent isotope in the sample, and λ is the decay constant of the parent isotope, equal to the inverse of the radioactive half-life of the parent isotope[14] times the natural logarithm of 2.

  • Earth’s geological history is long and complex… it is divided into hundreds of different eras, ages, epochs, etc.


So… we’ve got Fossils, and We Know How Old they Are

  • We can combine these two things to figure out the history of life on Earth!!!


Phylogenetic Trees

  • Phylogenetic trees are used to represent the most probable evolutionary relationships between a group of organisms.

  • They can be based on

    • Genetics

    • Fossils

    • Morphology (structure)


Two types of Evolution are Found in the Fossil Record

  • Gradual evolution is slow change over long periods.

  • Punctuated equilibrium means big changes can happen fast (in geology, fast means 100,000s of years!)


How do species change over time?

  • Phyletic speciation: gradual changes in a single species

  • Divergent Speciation: one species splits into two or more.

  • Both types appear in the fossil record


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