Chapter 18 Life in the Universe

Chapter 18 Life in the Universe The only place we know life exists is here on Earth One of humanity’s Big Questions is whether it exists elsewhere We can get some clues by considering life’s history here on Earth When we do, we can get an idea how likely life “as we know it” is But we should keep in mind that life as we know it may not be the only possible kind of life It is, however, the kind that we will be best able to recognize, if it does exist…

When did life arise on Earth?

When did life arise on Earth? The first evidence of life appears ~150 million years after the end of the Era of Heavy Bombardment This is not fossil evidence, but trace chemical evidence The evidence is in the ratio of carbon- 12 to carbon-13

Carbon isotope evidence for life In >3.8-billion-year-old rocks like these in Greenland there is a higher than normal ratio of 12C:13C Living things incorporate 12C more easily than 13C So the higher ratio is taken as indirect evidence for life