The earliest evidence for life on Earth dates to
A) about 4.5 billion years ago.
B) about 3.8 billion years ago.
C) about 2 billion years ago.
D) about 570 million years ago.
E) about 65 million years ago.
B
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Inside a space station in orbit around Earth:
a. there is no gravity because of the height of the station far above Earth. b. there is no gravity because the station is in orbit. c. gravity appears absent because everything is moving and accelerating together. d. objects have no mass because they are in orbit. e. gravitational effects feel the same as on Earth.
You are standing on a platform and a train approaches you, moving at a constant velocity. Its whistle is blowing continuously. The train does not stop at the platform, but it continues to move past the platform at a constant velocity. Which of the following statements are true about the frequency of the train's whistle that you hear?
1.The whistle's frequency that you hear increases continually as the train approaches the platform and then decreases continually after the train passes the platform. 2.The whistle's frequency that you hear seems to you to remain constant for the entire duration of the train's passage. 3.The whistle's frequency that you hear decreases continually as the train approaches the platform and then increases continually after the train passes the platform. 4.The whistle's frequency that you hear remains constant as the train approaches the platform and then decreases immediately after the train passes the platform, after which it remains constant at a lower pitch than it had originally.
If the north poles of two bar magnets are brought close to each other, the magnets will
A) attract. B) repel.
Most radio galaxies belong to Hubble's class ________
Fill in the blank(s) with correct word