Studies show that Venus may once have had an atmosphere and environment almost identical to Earth’s. Now, Venus has no water on its surface or in its atmosphere. How would Scientist 2 most likely explain the change in Venus’s atmosphere and environment?
F. Venus’s living beings were not able to stir the sun to bring new hydrogen to its core.
G. Venus’s sun entered its Red Giant phase much earlier in the planet’s development.
H. The carbon dioxide levels in the atmosphere dropped to levels that no longer supported photosynthesis.
J. Venus’s location to the sun made it more vulnerable to atmospheric and environmental changes.

Scientist 2
The sun will enter its Red Giant phase in about 7 billion years. However, new models suggest that Earth has less than a billion years before atmospheric carbon dioxide levels drop to levels that can no longer support photosynthesis. This would lead to a dramatic temperature increase. Once Earth’s average temperature rises to above 70°C, the oceans will evaporate and Earth’s water sources will be almost completely eliminated. One billion years is not long enough for humans to evolve in order to meet large atmospheric and environmental changes, or to develop the technology needed to make Earth habitable. In a billion years, atmospheric changes will eliminate all life on Earth as we know it. Humans need to accept the reality that advanced life flourishes for only a limited period of time. Science fiction—inspired plans to create space colonies or massive sunshades are unrealistic and will not likely be developed in the next billion years.