The Atmosphere
What did early Earth include?
Light gases such as hydrogen and helium
How Did Earth Form?
Scientists think that Earth began as a ball of dust, rock, and ice in space. Gravity pulled this mass together.
Why couldn't water remain a liquid in the beginning?
Earth's surface was too hot for water to remain a liquid.
When and where were single-celled organisms found?
Scientists found fossils of single-celled organisms in rocks that formed about 3.5 billion years ago.
What was the discovery of organisms about 2.5 billion years ago?
Many organisms began using energy from the sun to make food
Strong bursts of particles called solar winds
According to the scientists' hypothesis, the _____ formed from material knocked loose when a very young ____ collided with another object.
Moon, Earth
As Earth's surface cooled, the water vapor began to condse to form ______
Rain
What do scientists believe about all other life forms?
Scientists believe that all other life forms arose from these single-celled organisms.
As organisms released _______ , the amount of ______ in the atmosphere slowly grew
Oxygen, oxygen
What couldn't Earth's gravity hold?
Earth's gravity could not hold the light gases, and solar wind blew away Earth's first atmosphere
What did Earth do as it grew larger?
Its gravity increased, and it pulled in more dust, rock, and ice nearby.
What happened during early Precambrian Time?
Much of Earth's rock cooled and hardened
What did the atmosphere develop to help block the ultraviolet rays of the sun? What was the result?
An ozone layer. Shielded from the sun's rays, organisms could live on land.
Carbon dioxide, water vapor, nitrogen, and other gases to the atmosphere.
How was Earth's core formed?
Denser materials sank toward the center, forming Earth's dense, iron core.
Less than 500 million years after Earth formed, the rock at the surface formed _______
Continents
BONUS: What is photosynthesis? What is the ozone layer?
About 2.5 billion years ago, many organisms began using energy from the sun to make food. This process is called photosynthesis. One waste product of photosynthesis is oxygen. As organisms released oxygen, the amount of oxygen in the atmosphere slowly grew. Some oxygen changed into a form called ozone. The atmosphere developed an ozone layer that blocked the ultraviolet rays of the sun.
A ______ is a ball of dust, gas, and ice that orbits the sun.
Comet
The energy from these collisions with these materials raised Earth's ________ until the planet was very ______
Temperature, hot
What did scientists find because of the forces inside Earth?
Continents move very slowly