Fans of Doctor Who might be familiar with this beautifully poetic term that means the scent of rain on dry earth. It is etymologically derived from the Greek for stone (petros) and ichor, the blood of gods in Greek mythology. Though a poets dream, the actual term was derived by researchers who found that the distinctive and pleasing scent comes from an oil emitted into the soil from certain plants in dry spells. When it rains, the oil is released into the air, along with certain other compounds, producing that crisp, familiar smell of freshness and renewal.