The Earth Takes Shape

1. Pgs 48 -53 The Earth Takes Shape

2. The Solid Earth Takes Form • It is not easy to try to understand how our planet formed. • Scientists have gathered information from other galaxies and what they know about our Earth currently. • They believe the Earth formed from the accumulation of planetesimals over 10 million years.

3. The Effects of Gravity • The Earth is believed to have had an irregular shape when it was young(like a potato). • As matter accumulated the force of gravity increases and pushes heavier material to the center. • By the time a planet reaches the diameter of 350km it becomes spherical due to the force of gravity crushing the rock at its center.

4. The Effects of Heat • While accumulating planetesimals, the Earth’s temperature increased. • Also, radioactive material (present at the time of the solar nebula) radiates and collects in the interior of the Earth. • The energy inside the Earth heated it, but could not cool off fast enough and the rocky material began to melt.

5. The Earth and Its Layers • The young Earth, with liquid rock present, had heavy (dense) elements sink to the center of the planet. • This became the core and was made of elements like nickel and iron. • Lighter (less dense) elements floated toward the outside surface of the Earth.

6. The Earth’s Interior • The Earth is divided into three layers according to their composition. • The crust is the outermost layer ranging from 5 -100 km thick. • The mantle is below the crust and contains denser rocks than the crust. It ranges from about 100 – 2900 km. • The core is the center of the Earth and contains the densest materials like nickel and iron.

7. The Atmosphere Evolves • Other than life appearing, the biggest difference between young Earth and today is the atmosphere. • It has changed several times since its initial development.

8. Earth’s Early Atmosphere In the 1950’s, laboratory experiments on the origins of life were based on the hypothesis that Earth’s early atmosphere was largely made up of methane, ammonia, and water. Also, solar nebulas contain lots of hydrogen and the Earth was thought to contain many hydrogen containing compounds. New evidence is suggesting that 85% of Earth’s matter is similar to meteoroids and 15% is from comets.

9. Volcanic Gases • During the final stages of formation, the Earth was hit with planetesimals. • The ground was hot and partially molten. • It was probably venting gases like water vapor and carbon dioxide (two gases found in volcanic eruptions). • The Earth’s first atmosphere was probably mostly water vapor and carbon dioxide.

10. The Role of Impacts • Planetesimal impacts may have helped the release of gases from inside the Earth. • They also could have released gases that were on the earth and pushed them out into space. • Heavy elements on the surface like iron react with water vapor and give off hydrogen (allowing it to escape into space) • Comets also brought many elements like carbon, hydrogen, oxygen, and nitrogen to the Earth.

11. Earth’s Second Atmosphere • Once the Earth’s surface cooled, the second atmosphere could take shape. • This atmosphere got its gases from volcanoes and comets. • Volcanoes emitted large amounts of water vapor, chlorine, nitrogen, sulfur and carbon dioxide.

12. Earth’s Current Atmosphere • The current atmosphere formed with the help of UV radiation. • UV radiation can break down molecules in the air. • The pieces were washed out into shallow seas and tide pools by rain. • Eventually, a rich supply of these pieces of molecules collected in areas forming a solution sometimes called the “primordial soup”

13. The Source of Oxygen • There was no ozone in the early atmosphere but water offered some protection from UV rays. • In pools of water, complex molecule may have been able to form and life began about 4.6 – 3.9 billion years ago. • Soon photosynthesizing organisms evolved and began producing oxygen as a waste product. • The amount of oxygen grew rapidly to where it is today. • The beginning of life changed our atmosphere.

14. Oceans and Continents • The oceans were formed once the Earth was cool enough for rain to fall. • At first there was just a giant ocean on the surface of the Earth. • Continents developed after numerous times of heating and cooling rock material. • Eventually, the less dense rock rose to the surface to from the continents.

15. The Growth of Continents • The layers of rock on the surface of the Earth gradually thickened to the point they were above the ocean surface. • However, convection currents continued and the land changed with its motion and continues to do so today.