The Geologic Time Scale The Geologic Time Scale and Early Earth Section and Early Earth Section

ReviewReview

What is the geologic time What is the geologic time scale?scale?

►A record of the life forms and A record of the life forms and geological events in Earth’s history. geological events in Earth’s history.

True or False?True or False?

► In order to develop the geologic time In order to develop the geologic time scale, scientists studied rock layers scale, scientists studied rock layers and fossils worldwide and placed and fossils worldwide and placed Earth’s rock layers in order by relative Earth’s rock layers in order by relative age. Later, radioactive dating helped age. Later, radioactive dating helped them determine the absolute ages of them determine the absolute ages of the divisions. the divisions.

►TRUE! TRUE!

What are the basic units into What are the basic units into which the geologic time scale is which the geologic time scale is

divided?divided?

►Era’s and periodsEra’s and periods

What are the 4 Era’s introduced What are the 4 Era’s introduced in your book?in your book?

►PrecambrianPrecambrian►PaleozoicPaleozoic►MesozoicMesozoic►CenozoicCenozoic

True or False?True or False?

►Scientists hypothesize that Earth formed Scientists hypothesize that Earth formed at a different time than the other planets at a different time than the other planets and the sun around 2 million years ago.and the sun around 2 million years ago.

►FALSE!!!FALSE!!!

►The hypothesis states the Earth was The hypothesis states the Earth was formed at the same time as the other formed at the same time as the other planets and the sun around 4.6 billion planets and the sun around 4.6 billion years ago! years ago!

What is a comet?What is a comet?

►A ball of dust and ice that orbits the A ball of dust and ice that orbits the sun.sun.

How did volcanic eruptions and How did volcanic eruptions and comets change Early Earth?comets change Early Earth?

►They released carbon dioxide and They released carbon dioxide and water vapor into the atmosphere. water vapor into the atmosphere.

What do scientist think were the What do scientist think were the first organisms to evolve on first organisms to evolve on

Earth?Earth?

►Bacteria-like organismsBacteria-like organisms