A "flash of light" marks the beginning of life in humans, according to a study conducted by researchers from Northwestern University in Chicago.
Scientists were able to capture in video the light or "fireworks" that break out when a human egg is activated by sperm, which mimics the process of conception.
During fertilization, the amount of calcium in the egg increases, and the egg releases zinc. As the zinc is released, it bursts into light. This happens every time conception occurs.
This phenomenon has been observed in mice, but this is the first time it was observed in humans. However, the researchers did not use actual sperm cells for the study. Instead, they used sperm enzymes.
"We discovered the zinc spark just five years ago in the mouse, and to see the zinc radiate out in a burst from each human egg was breathtaking," study author Teresa Woodruff said in a statement.
The researchers observed that the flash was brighter for eggs that were of good quality. They also reported that only mature eggs exhibited the flash; those that were not mature did not emit light.
The study holds great significance especially in in vitro fertilization because doctors will be able to tell which eggs are of good quality by simply observing or comparing the zinc spark.
"It's a way of sorting egg quality in a way we've never been able to assess before," Woodruff said.
This helps couples avoid heartache when they try to conceive through in vitro fertilization, especially when there is yet no way to tell if the egg cells used are healthy enough. Most of the time, couples are not aware of the quality of the egg until the pregnancy has started.
"These results demonstrate critical functions for zinc dynamics and establish the zinc spark as an extracellular marker of early human development," the authors concluded.
The study was published in the April 26 issue of the journal Scientific Reports.