Earth's early air and oceans

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Oxygen in the air over time (Smithsonian, NASA)

   Time	Oxygen in the air
   before about 2.7 billion years ago	almost none
   about 2.4 billion years ago	first fills the air (NASA)
   about 600 million years ago	about one-fifth of today's level
   today	21%

2. 1.

   Using the table, about how long after cyanobacteria began (about 2.7 billion years ago) did oxygen first fill the air (about 2.4), by Bo's math?

   • About 3 years
   • About 300 million years
   • About 5.1 billion years
   • No time; it was instant
3. 2.

   Using the table, about how long did it take from the first oxygen in the air (2.4 billion years ago) to one-fifth of today's level (600 million), by Esme's math?

   • About 1.8 billion years
   • About 1.8 million years
   • About 3 billion years
   • About 600 million years
4. 3.

   Why did oxygen take hundreds of millions of years to build up in the air, by Jun's reading (Smithsonian)?

   • Volcanoes kept taking oxygen in
   • It first reacted with methane and with iron in rocks
   • Photosynthesis used up oxygen
   • The air already held plenty
5. 4.

   Drawing of reddish rock layers. Smithsonian: after about 300 million years of oxygen-making, reddish redbeds formed. What do they show, by Kira's reading?

   • Oxygen had built up enough to rust iron in rocks
   • The rocks were heated by the Sun
   • Volcanoes were giving off oxygen
   • There was still no oxygen
6. 5.

   Carbon dioxide + water + sunlight → sugar + oxygen. Cyanobacteria take in carbon dioxide and give off oxygen. How did they change the early air, by Milo's reading?

   • More carbon dioxide, less oxygen
   • Less carbon dioxide, more oxygen
   • More methane from their breathing
   • No change
7. 6.

   Today's air and a lifeless model. If volcanoes had kept adding gas but no life had made oxygen, what would Earth's air be like today, by Noah's reading?

   • Just like today's, 21% oxygen
   • Pure oxygen
   • Rich in carbon dioxide, with almost no oxygen
   • No gases
8. 7.

   Earth formed about 4.6 billion years ago, and its surface cooled enough for water about half a billion years later (Smithsonian). About when could oceans begin to collect, by Pia's math?

   • About 5.1 billion years ago
   • Right at 4.6 billion years ago
   • About 0.5 billion years ago
   • About 4.1 billion years ago
9. 8.

   The young Sun gave about 70% of today's light. A dimmer Sun means a colder Earth unless what, by Ren's reading (Smithsonian)?

   • Unless greenhouse gases trap extra heat
   • Unless oxygen fills the air
   • Unless volcanoes make oxygen
   • Unless the oceans freeze
10. 9.

    1% of today's level, then one-fifth (20%) of today's level. Oxygen rose from about 1% of today's level to about one-fifth of it. How many times larger is that, by Tala's math?

    • About 100 times
    • About 2 times
    • About 5 times
    • About 20 times
11. 10.

    NASA describes oxygen oases: patches where cyanobacteria made oxygen before it spread worldwide. What does this suggest, by Zee's reading?

    • The whole air filled with oxygen at once, with no patches
    • Oxygen built up in patches first, then spread
    • Volcanoes made the patches
    • The patches took in oxygen