CH. 9.2 Life and Geologic Time Mr. Perez

Important Vocabulary Adaptation Geologic time scale Epoch Era Period Eon Trilobite

Geologic Time Scale The appearance or disappearance of types of organisms throughout Earth’s history marks IMPORTANT occurrences in geologic time. The geologic time scale was made by paleontologists. This time scale divides Earth’s history into time units based on the life-forms that lived only during certain periods. The time scale is not only based on life-forms living in certain periods– sometimes, life-forms are not present, so certain time periods of the geologic time scale are based on other information/criteria

Geologic Time Scale If we were to create a geologic time scale based on the life time of a human, it might look something like this… Life Eon Non-Talking EraTalking Era Crawling Period Teething Period School PeriodWork PeriodRetirement Period First tooth Epoch First molar Epoch Element ary Epoch Seconda ry Epoch Colleg e Epoch Bus Boy Epoch Man ager Epoc h CEO Epoch

Subdivisions of Geologic Time The oldest rock on Earth contain NO fossils. Then, for millions of years after the first appearance of fossils, the fossil record remained sparse. Later, in Earth’s history came an explosion in the abundance and diversity of organisms. The FOUR subdivisions of geologic time are: 1.Eons 2.Eras 3.Period 4.Epochs

Subdivisions of geologic time Eons- longest subdivision based on the abundance of certain fossils Examples- Hadean eon, Archean eon, Proterozoic eon, Phanerozoic eon, Era- second longest subdivision based on the major, striking, and worldwide changes in the types of fossils present Examples- Paleozoic era, Mesozoic era, Cenozoic era Eras are divided into periods Refer to p. 259 Figure 12

Subdivisions of Geologic Time Periods- units of geologic time based on the types of life existing worldwide at the time. Examples- Cambrian, Ordovician, Jurassic, Cretaceous, Triassic, Devonian Periods are divided into smaller groups called epochs Epochs- units of geologic time based on differences in life-forms, but some of these differences can vary from continent to continent Examples- Paleocene, Eocene, Oligocene, Miocene, Holocene Refer to p. 259 Figure 12

Identify when each development in Earth’s history occurred EventEonEra (if identified) Period (if identified) First lifeArcheann/a First trilobitesPhanerozoicPaleozoicCambrian First flowering plants PhanerozoicMesozoicCretaceous Refer to p. 259 Figure 12

Trilobites Small, hard shelled organisms Crawl on the seafloor or swam through water 2cm – 7cm in length, 1cm – 3cm in width Considered to be index fossils because they lived over vast regions of the world during specific periods of geologic time.

Trilobites Body has three lobes along the length Head= cephalon Segmented middle section = thorax Tail = pygidium

Changing Characteristics of Trilobites Trilobites lived on Earth for over 200 millions years. Throughout the Paleozoic Era, some trilobite species became extinct and other new species evolved, showing different characteristics.

Trilobite Eyes Trilobites might have been the first organisms that could view the world with complex eyes… The position of eyes on an organism gives clues as to where it must have lived Eyes on the back of the head indicate a bottom dweller Eyes on the front of the head indicate an active swimmer In most species, trilobite eyes were located midway on the head This indicates that trilobites could both crawl on the ocean floor and swim through the water

Trilobite Eyes As time passed, the eyes in trilobites changed. In many species, the eyes became smaller Some even lost their eyes completely— these species probably lived underground and did not need eyes In other species, the eyes became more complex Aeglina, a species of trilobite, developed large compound eyes (like insects) Other trilobites developed stalks that held the eyes upward

Trilobite Bodies Trilobite bodies and tails also underwent changes in form through time Olenellus: Lived during the Early Cambrian Period Had an extremely segmented body It is thought to have been a primitive trilobite

Adaptations Adaptations are characteristics of an organism that increase its chances of survival in its environment According to Charles Darwin’s natural selection, a species of animal, overtime, will adapt to its environment… The trilobite’s changing body, eyes, and tail are an example of an adaptation Charles Darwin studied the beak color and size of finches in the Galapagos islands

Resources Florida Science Grade 7 Glencoe Science & McGraw Hill Publishing Google Images