Astronomy 19.4

Imagine that we receive a radio message from a civilization around a star about 40 light years from Earth. If we reply right away, how long will it be between the time THEY sent the message and the time they receive our reply?

80

Scientists think that the life we have on Earth today originated some time between 3.5 and 3.8 billion years ago. Yet the solar system and the Earth are known to be at least 4.5 billion years old. Which of the following is one reason life as we know it had to wait until 3.5 to 3.8 billion years ago to get going?

Before 3.8 billion years ago, Earth was experiencing heavy bombardment from space.

Scientists are impressed with extremophiles, life forms that can survive under what seems to humans to be extremely unpleasant conditions. In which of the following environments have we not found life?

Conditions resembling the photosphere of the Sun (about 5,500 C)

Which of the following is a biomarker that could be used from an observatory around a nearby star, with the right equipment, to identify the Earth as a planet with life?

Free oxygen in the Earth's atmosphere

Chemically, the process leading to life on Earth began with lots of liquid water and _______.

Helium

Astronomers have discovered planets orbiting Proxima Centauri, the star closest to the Sun. This is a star of spectral type M, with 12% the mass of the Sun and 15% the size of the Sun. Describe the star's habitable zone.

It would be in about the same place as the Sun's asteroid belt.

In the early 1950's, Stanley Miller and Harold Urey conducted a series of pioneering laboratory experiments involving simulations of the early Earth. What did these experiments reveal?

That under conditions approximating the early Earth's environment, building blocks of life can form

What discovery has made astronomers more optimistic about our prospects of finding life out there?

The discovery of planets around thousands of stars in our Galaxy

The Drake Equation allows astronomers to estimate what?

The number of civilizations out among the stars with which we might communicate

What discovery about Saturn's moon Enceladus has encouraged astronomers to think of that moon as a possible place where life might exist?

There are plumes of salty vapor coming from cracks in Enceladus' surface.

In which of the following places have astronomers NOT found evidence for the building blocks of life (organic compounds)?

We have found evidence for such materials in all of these sites.

Photosynthesis releases a particular gas as a byproduct. What gas is that? ________

oxygen

Which band of the electromagnetic spectrum do astronomers say is likely to be the best for communication between civilizations at different stars? _________. It is cheap, there is little competition from the universe emitting much of it, and it penetrates planetary atmospheres well.

radio waves

For the complex biochemical reactions of life (as we know it) to happen, a solvent is required. What is that solvent for life on Earth?

water