Chapter 14 The History of Life

History in Rocks It is believed that the earth is about 4.6 billion years old. The oldest rocks that have been found on Earth formed about 3.9 billion years ago. Fossils (evidence of an organisms that lived long ago) tell us information about the earth.

How Fossils Form 1. Trace fossils – a marking left by an animal and may include a footprint, a trail, or a burrow.

2. Casts – when minerals in rocks fill a decayed organism, they make a replica, or cast, of the organism.

3. Petrified fossils – minerals sometimes penetrate and replace the hard parts of an organism, producing copies of them.

4. Imprints – a thin object that falls into sediment can leave an imprint when the sediment hardens into rock.

5. Amber-preserved and frozen fossils – an entire organism was quickly trapped in ice or tree sap that hardened into amber.

6. Molds – when an organism is buried in sediment and then decays, leaving an empty space.

The Age of a Fossil Relative dating – If the rock layers have not been disturbed, the layers at the surface must be younger than the deep layers. Scientists can determine the order of appearance and extinction of the species that formed fossils in the layers.

Radiometric dating Scientists use radiometric dating techniques utilizing the radioactive isotopes in rocks or fossils.

Radioactive parent isotopes and their stable daughter products Radioactive Parent Stable Daughter Potassium 40 Argon 40 Uranium 235 Lead 207 Uranium 238 Lead 206 Carbon 14 Nitrogen 14 Rubidium 87 Strontium 87 Thorium 232 Lead 208

Write three facts about each era and the years they took place 1. Precambrian era 2. Paleozoic era 3. Mesozoic era 4. Cenozoic era

The Origin of Life Early Ideas Spontaneous generation – the idea that nonliving material can produce life. Meat left out decaying, “produced” maggots. Francsco Redi’s experiment disproved this idea.

Many scientists still believed that microorganisms (bacteria) could spontaneously be produced. Louis Pasteur’s experiment disproved this idea.

The Origin of Life Modern Ideas Biogenesis – living organisms come only from other living organisms. In 1953, Miller and Urey performed an experiment to see if the conditions of early earth could produce organic (carbon containing) molecules. After a week of performing their experiment, several kinds of amino acids and sugars appeared.

The Origin of Life Sidney Fox performed experiments to see if these complex organic molecules could combine to produce cells. He was able to produce protocells after heating the organic molecules. Protocells – a large, ordered structure, enclosed by a membrane, that carriers out some life activities, such as growth and division.

Protocell RNA Phospolipid bilayer

The First True Cells The first cells are thought to have been heterotrophic prokaryotes. They used the organic molecules for food that were abundant on earth. However, when the organic molecules were gone, autotrophic prokaryotes became abundant and used chemosynthesis to make glucose.

Next probably came the photosynthetic prokaryotes that used sunlight to make glucose. These organisms produced oxygen and affected life on earth.

Endosymbiont theory Complex eukaryotes probably evolved from prokaryotes that incorporated mitochondria and chloroplasts for their energy making ability. Mitochondria and chloroplasts have DNA similar to prokaryotes.