2 The Planet FormsOur Journey Begins: Scientists hypothesize that Earth formed at the same time as the other planets and the sun, roughly 4.6 billion year ago.radioactive dating - oldest rocks found are about 4 billion years oldscientists think Earth formed even earlierEarth and the moon are about the same ageWhen earth was very young, it collided with a large object. The collision threw a large amount of material from both bodies into orbit around Earth. The material combined to form the moon.
3 The Planet FormsMoon Rocks! - brought back to Earth by astronauts during the 1970sradioactive dating shows that the oldest moon rocks are about 4.6 billion years old.Scientists infer that Earth is about 4.6 billion years old- only a little older than those moon rocksEarth Takes Shape:Scientists think that Earth began as a ball of dust, rock, and ice in space.What force caused the materials that formed Earth to come together?gravity pulled this mass together
4 The Planet Forms As Earth grew: its gravity increased pulling in dust, rock, and ice nearbyobjects made of these materials struck Earth at high speedskinetic energy was changed to thermal energyenergy caused the Earth’s temperature to rise until the planet was very hotdenser materials sank toward the center, forming Earth’s dense, iron coreEarth continuously lost heat to the cold of spaceless dense, molten material hardened to form Earth’s outer layers- the solid crust and mantle.
5 The Planet Forms Earth’s Surface Forms As Earth traveled around the sun, its gravity also captured the gases such as hydrogen and helium.this first atmosphere was lost when the sun released a strong burst of particles - blowing away Earth’s first atmosphereEarth’s Surface FormsDuring the first several hundred million years of Precambrian Time, an atmosphere, oceans, and continents began to form.
6 The Planet Forms The Atmosphere a second atmosphere formed made up mostly of carbon dioxide, water vapor, and nitrogenvolcanic eruptions released carbon dioxide, water vapor, and other gases to the atmospherecollisions with comets added other gassesA comet is a ball of dust and ice that orbits the sun The ice in a comet consists of water and frozen gases, including carbon dioxide
7 The Planet Forms The Oceans at first, Earth’s surface was too hot for water remain as a liquidevaporated into water vaporas Earth’s surface cooledthe water vapor began to condense to form rainaccumulate to form an oceanOver time, the oceans affected the composition of the atmosphere by absorbing much of the carbon dioxide
8 The Planet Forms The Continents Less than 500 million years after Earth’s formation, the less dense rock at the surface formed large landmasses called continentsScientists have found that the continents move very slowly over Earth’s surface because of forces inside Earth.This process is called continental driftmovement is very slow – only a few cm per yearEarth’s landmasses have repeatedly formed, broken apart, and then crashed together again, forming new continents
9 The Planet Forms Life Develops: Scientists cannot pinpoint when or where life began on Earthscientists have found fossils of single celled organisms in rocks that formed about 3.5 Ba years agoearliest life forms were probably similar to present-day bacteriaScientists hypothesize that all other forms of life on Earth arose from these simple organisms
10 The Planet Forms2.5 Ba years ago - many organisms began using energy from the sun to make their own foodThis process is called photosynthesiswaste product of photosynthesis is oxygen.As organisms released oxygen into the air, the amount of oxygen slowly increasedProcesses in the atmosphere turned some of this oxygen into ozoneatmosphere developed a layer rich in ozone that blocked out the deadly ultraviolet rays of the sunnow shielded, organisms could live on land