What did Earth's first atmosphere consist of?
Light gases such as hydrogen and helium
What was water like on Earth at first?
It was water vapor because it was too hot for liquid water
How do scientists hypothesize that the moon formed?
It formed from material that was knocked loose when a very young Earth collided with another object
Aside from respiration, why was the addition of oxygen to the atmosphere through photosynthesis important?
It created an ozone layer that blocks ultraviolet rays from the sun
What was the temperature like on the newly formed Earth?
It was so hot that scientists think Earth might have melted
How long ago did photosynthesis develop?
About 2.5 billion years ago
How old are the oldest rocks on Earth?
About 4 billion years old
What happened to denser materials on Earth?
They sank towards the center and formed Earth's dense, iron core
What happened to less dense materials on Earth?
Molten material hardened over time and formed Earth's outer layers
How old are the oldest moon rocks?
About 4.6 billion years old
What is a comet?
A ball of dust, gas, and ice that orbits the sun
What happened to water vapor in the atmosphere as Earth cooled?
It condensed to form rain which accumulated and formed the oceans.
How did Earth's second atmosphere form?
Volcanic eruptions and collisions with comets added carbon dioxide, water vapor, nitrogen, and other gases to the atmosphere.
How old do scientists think Earth is?
About 4.6 billion years old
What is a waste product of photosynthesis?
Oxygen
How old are the single-celled organisms scientists found in rocks?
About 3.5 billion years old
How do scientists think Earth formed?
It began as a ball of dust, rock, and ice in space that was pulled together by gravity
When did continents form?
Less than 500 million years after Earth formed
What happened to Earth's first atmosphere?
It was blown away by particles from the sun (solar wind)