**Optional.** Scientific ideas about how life began

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Table, Early Earth timeline (NASA), with columns Event, When

   Earth forms, about 4.5 billion years ago; Possible earliest signs of life, about 4 billion years ago; Pilbara stromatolites, Australia, about 3.5 billion years ago; Miller–Urey paper in Science, May 15, 1953.

2. 1.

   Using the timeline, about how long after Earth formed did the Pilbara stromatolites form, by Bo's math?

   • About 3.5 billion years
   • About 8 billion years
   • About 0.1 billion years
   • About 1 billion years
3. 2.

   NASA: Earth is about 4.5 billion years old, and life may date to about 4 billion years ago. About what share of Earth's history might life span, by Esme's math?

   • About 50%
   • About 11%
   • About 113%
   • About 89%
4. 3.

   Using the timeline, about how many years passed from Miller's 1953 paper to 2026, by Jun's math?

   • About 73 years
   • About 1,953 years
   • About 37 years
   • About 3,979 years

5. Table, The Miller–Urey experiment (NASA), with columns Part, What it stood for or gave

   Flask of water, an early ocean; Methane, ammonia, hydrogen and water vapor, an early atmosphere, as Urey proposed; Electric sparks, lightning; Result in 1953, 5 amino acids identified; Re-analysis in 2008 of a sibling experiment, 22 amino acids.

6. 4.

   Why did Urey choose methane and ammonia for the model atmosphere, by Kira's reading (NASA)?

   • They are the main gases in the air we breathe today
   • Living cells gave them off at that time
   • Giant-planet spectra showed air rich in them
   • Fossils showed they were in early air
7. 5.

   NASA: volcanoes give off mostly water vapor and carbon dioxide, not methane and ammonia. What does that suggest about the 1953 setup, by Luz's reading?

   • The question of life's origin is now settled
   • The experiment did make living cells in the flask
   • Volcanoes make amino acids directly
   • Early Earth's air may have been less like Urey's mix
8. 6.

   RNA, DNA and a protein, with the jobs each can do. Why is RNA a good candidate for the first genetic molecule, by Noah's reading (NASA)?

   • It makes up most of a cell's water
   • It needs both DNA and proteins before it can ever form
   • It has vanished from cells today
   • It can carry genetic data and act as an enzyme
9. 7.

   A pond, a tide pool, a hot spring and a seafloor vent chimney. NASA: tests with vent-like minerals made RNA strings up to four units long at room temperature. What is a concern, by Pia's reading?

   • The strings were far too long to count as real RNA molecules
   • Real vents are much hotter, and heat could destroy RNA
   • Room temperature is hotter than vents
   • The test settled how life began
10. 8.

    RNA, DNA and a protein, with the jobs each can do. What question does the RNA world idea leave open, by Ren's reading (NASA)?

    • Whether RNA exists in living cells
    • How RNA itself first formed from simpler molecules
    • Whether DNA stores genetic data
    • Whether stromatolites are layered rocks made by microbes

11. Table, Early Earth timeline (NASA), with columns Event, When

    Earth forms, about 4.5 billion years ago; Possible earliest signs of life, about 4 billion years ago; Pilbara stromatolites, Australia, about 3.5 billion years ago; Miller–Urey paper in Science, May 15, 1953.

12. 9.

    What are stromatolites, by Tala's reading (NASA)?

    • Crystals grown in hot springs with no life
    • Bones of the first animals
    • Ripples left by waves on sand
    • Layered rocks built by mats of microbes growing layer by layer
13. 10.

    Why do scientists look for stromatolite-like mounds on Mars, by Zee's reading (NASA)?

    • They show that plants once grew on Mars
    • They mark where meteorites landed
    • They form where liquid oceans exist today
    • Such mounds could be a sign of ancient microbial mats