About how old is Earth?

1. About how old is Earth? • 6000 years • One million years • One billion years • 5 billion years • 14 billion years

2. How do scientists tell the age of different rocks on Earth? • They look at the layering of rocks, which is similar in many places on Earth. Lower layers were formed first, upper layers afterward. • They look at the density of rocks. Density gradually increases as Earth ages. • Some elements gradually change into other elements due to radioactivity. This rate can be studied in the lab, and then applied to rocks to see how old they are • All of the above. • A and C

3. How do we know Earth’s age? • Radiometric dating of the oldest Earth rocks • Radiometric dating of Moon rocks • Radiometric dating of meteorites • All of the above

4. When did life begin on Earth? • Thousands of years ago • Millions of year ago • Between 3 and 4 billion years ago • We don’t really know.

5. How do we know when life first arose on Earth? • Counting tree rings • Radiometric dating of fossils • The age of the rocks in which the fossils are found (determined from layering and radiometric dating of the rocks) • A and B

6. Why is it unlikely that life could have arisenbefore 3-4 billion years ago? • Earth was too hot. • Earth was being bombarded by planetesimals that formed the solar system. • Earth may not have had much water yet. • All of the above.

7. How do we know that life evolved from simple to more complex? • Like the evolution of stars, we study the mechanism (DNA and mutation, rather than fusion, gravity, etc.). • We look for clues of various stages (fossils, rather than red giants and white dwarfs). • We make predictions of what should be found, then go look (the scientific method). • All of the above. • A and B

8. All living organisms known today evolved from a common ancestor that lived long ago. • True • False

9. How do we know that all living organisms have evolved from a common ancestor from long ago? • The fossil record shows sequences of organisms of similar appearance that change with time. • DNA shows remarkable similarities among all life forms. • DNA is more similar among closely related forms. • Not only useful but also useless or “junk” DNA is found to be similar among different organisms. • All of the above.

10. How does evolution affect people today? • It doesn’t–evolution takes a long time. • If you get the flu this year you can still get sick next year because the virus evolves. • The AIDS virus mutates quickly, making it hard to fight with drugs. • Mutation causes antibiotics to gradually lose their effectiveness against certain infections. • B, C, and D

11. Do you see a similarity between studying theevolution of the universe and the evolution of life? The redshifts of galaxies show the universe is expanding.The Big Bang theory explains how it happens. The fossil record shows that life changes over time. Natural selection theory explains how that works. • True • False

12. How did life arise? • We don’t know. • DNA studies suggest that the first life may have lived in hot water near volcanic vents. • This is an object of scientific study. • All of the above. • B and C

13. What suggests there couldbe life on Mars? • Evidence of liquid water, and evidence that there was more water in the past. • Mars has the next best climate than Earth. It is colder than us but was warmer in the past. • Mars has an atmosphere. • All of the above. • A and C

14. Is there other intelligent life in the universe? • Yes; Earth has already been visited by intelligent beings. • No; Earth is unique, and conditions similar to Earth’s cannot be found elsewhere. • We don’t know yet.

15. In 2020, a spacecraft lands on Europa and melts its way through the ice into the Europan ocean. It finds numerous living microbes, along with a few larger organisms that feed on the microbes. • This is likely because biosignatures were already detected on Europa by the Voyager 2 spacecraft. • This could happen because there is evidence for an ocean underneath the icy surface of Europa and water is a good place to look for life. • This is fantasy because it would take more than 20 years for a spacecraft to reach Saturn using current rocket technology. • This is fantasy because the X-ray emission from Saturn has effectively sterilized all the moons around it.

16. In 2030, someone discovers a way to build a rocket that burns coal as its fuel and can travel at half the speed of light. • This is possible because rocket technology is constantly improving. • This is possible because new power generators using coal are becoming increasingly more efficient. • This is fantasy because purely chemical burning cannot release enough energy to achieve such speeds. • This is fantasy because Einstein showed that it is impossible to travel faster than a fraction of the speed of light. • This is fantasy because there are no brilliant teenagers anymore.

17. In the year 2750, we receive a signal from a civilization around a nearby star telling us that the Voyager 2 spacecraft recently crash-landed on their planet. • This is a possible because Voyager 2 was deliberately aimed at nearby stars as it left the solar system. • This is fantasy because astronomers have shown that there are no other civilizations in the universe. • This is fantasy because Voyager 2 will take tens of thousands of years to reach the nearest stars. • This is fantasy because there are no stars within 750 light years of the Sun.