Aim: How can we analyze the geologic time scale?

Measuring Time The Earth - 4.6 billion years old Geologic time is divided into sections Each section shows a specific change in life or in the Earth’s surface

Giving Time a Name Largest sections are called “eons” “Eons” are divided into “eras” “Eras” are divided into “periods” “Periods” are divided into “epochs”

What do you know? In Pairs Are there any geologic time sections that you have heard of? What are they?

How is Time Divided? Major changes in Earth’s history mark the boundaries between the sections Most sections have been divided because a major organism developed or went extinct.

Extinction Extinction = the death of every member of a species Lack of food Lack of space Environmental changes 99.9% of all species that have lived on Earth have gone extinct

Mass Extinction Mass extinction = the extinction of many species at the same time It can be caused by gradual changes in climate or ocean currents (Uniformitarianism) Or by catastrophic events, like an asteroid hitting the earth and blocking out the sun (Catastrophism) Can you think of an example of a mass extinction?

Precambrian Time

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Precambrian Time Time from the formation of the Earth (4.6 billion years ago) to 544 million years ago The Earth was very different then At first, there was no no oxygen or living things Then the first organisms appeared in the oceans 3.6 billion years ago They were called Prokaryotes

Prokaryotes Only one cell and no nucleus Cyanobacteria, were the first organisms on Earth Through photosynthesis, they released oxygen As oxygen began to build up, the ozone was formed The ozone protects the Earth against the sun’s harmful rays (deadly to land organisms) Now organisms could live on land too!

Eukaryotes After another 1 billion years, more complex organisms developed They were called Eukaryotes Many cells with a nucleus Evolved into organisms on Earth today

Paleozoic Era Began 542 million years ago and ended 251 million years ago Divided into 6 periods

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Paleozoic Era Many new life forms appeared during the 1st period, the Cambrian Period = “Cambrian Explosion” For the first time on Earth, organisms had hard parts (shells, exoskeletons) Some organisms that were alive during this period still exist today (ferns and salamanders) but they were giants!

Permian Extinction The largest mass extinction. 251 million years ago end of the Paleozoic Era and the start of the Mesozoic Era Scientists are not sure what caused this mass extinction (maybe climate change & volcanoes) 90% of ocean life and 78% of land life died Reptiles and amphibians survived!

Mesozoic Era Began 251 million years ago Surviving reptiles and amphibians evolved into many other species (like dinosaurs) = “Age of Reptiles”

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Cretaceous-Tertiary Extinction Another mass extinction happened 65.5 million years ago Marked the end of the Mesozoic Era and the beginning of the Cenozoic Era All of the dinosaurs and half of the other animals & plants went extinct Scientists think an asteroid hit Earth, the dust clouds blocked out the sun, plants died, then herbivores, then carnivores.

Cenozoic Era Began 65 million years ago and continues today

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Cenozoic Era Scientists know the most about this Era because the fossils are in the top rock layers and are easier to find Land & climate has changed a lot What big change will happen that will end this era & start the next?