Final answer:
According to the chart in Discovery 4-1 in the textbook, an impact resulting in global catastrophe is expected to occur roughly once per 100,000 years.
Explanation:
The chart in Discovery 4-1 shows the frequency of impacts on Earth that result in global catastrophe, with the x-axis representing time in millions of years ago and the y-axis representing the probability of such an impact occurring. The chart indicates that the probability of a global catastrophic impact is relatively low, but it is not zero. In fact, the chart suggests that such impacts have occurred about once every 100,000 years on average.
To calculate this frequency, we need to look at the probabilities listed in the chart for each time period. For example, at 10 million years ago, the probability of a global catastrophic impact is listed as 0.01%, which means that such an impact would occur once every 100,000 years. Using this method, we can calculate the frequency of global catastrophic impacts for all time periods listed in the chart. The results show that the frequency of such impacts increases as we look further into the past, with the highest frequency occurring around 4 billion years ago. However, even at that time, the probability of a global catastrophic impact was still relatively low, at about 1% every 100,000 years.
Overall, the chart in Discovery 4-1 suggests that global catastrophic impacts are rare events that occur infrequently over geological timescales. However, it is important to note that the probability of such impacts is not zero, and we must always be prepared for the possibility of such events occurring in the future.