4.54 billion years 4.60 billion years First life 3.8 billion-year-old First hominids 6-7 mya Age of universe: 13.7 bya

Decoding Evidence Activity 4 stations Group of 2 Provide a brief description of each evidence Anticipation: Collectively, what conclusion can you deduce about Earth from these evidence?

How do we know the Earth is round? ies (1:13 to 4:06)

Earth’s axis of rotation viewed from North pole Earth rotates counter- clockwise viewed from South pole Earth rotates clockwise Is 23.5 o tilted SUN Earth rotates eastward toward the Sun

How rotation differs from revolution? RotationRevolution The turning of an object around an imaginary axis running through it E.g. Earth’s rotation takes 24 hrs The rotation of an object around an external axis (e.g. another object) E.g. Earth’s revolution around the Sun is days Leap year anyone?

When it is summer in the northern hemisphere, it is winter in the southern hemisphere. Why? Watch: MIT video

Reason for seasons Answer: because of Earth’s tilt In summer months: Northern hemisphere toward the Sun In winter months: Northern hemisphere away from Sun The opposite happens to Southern hemisphere Earth’s orbit around the sun is elliptical (oval or egg-shaped) Our winter = Earth closest to sun Our summer = Earth furthest from the sun

Please read Activity 7-2 p 285 for tomorrow Bring your textbook

Hands-on exploration: Activity 7-2 p 285 Examining the effect of Earth’s tilt on the differential amount of sunlight received on Earth’s surfaces Answer question 1-4 for HW

Extra slides if time permit

Why Earth keeps on spinning? Has to do with the way it was formed Formed from spinning gas and dust Inertia makes our planet keep on spinning unless there is a force to stop it Axis of rotation

A tour beneath our feet 5o08

Solstices Solstice occurs when the Sun shine directly on one of the two tropics because the tilt of the Earth’s axis reaches its maximum angle compared to the Sun During the June Solstice the rays of the Sun shine directly on the Tropic of Cancer; longest day Occur on June 21 and Dec 21 During the December Solstice the Sun’s rays shine on the Tropic of Capricorn; longest night

Equinox As the Earth moves around its orbit, it reaches two points during the year where the tilt of its axis causes it to be straight relative to the Sun. Thus, the Sun will shine directly on the equator On Mar 20 and Sep 22