MTL - Space Doctor: The National Hero is a Girl - Chapter 1603 directly said

Yan Xi was the eldest young lady of Beiqiao City’s top four families, the Yan family. Despite her talents, she was sickly and destined to die young. She was an unattainable dream girl for many.

One day, she had a dream, and the setting was in a novel. In the novel, for the sake of alleviating his pain of losing his wife, and soon his daughter as well, her father adopted a girl named Chen Xiangxiang who looked just like her. The girl was docile as a deer and very therapeutic, which made her all the more lovable. This girl became her substitute, and after a series of heart-wrenching incidents, everyone, from her father, brother, fiance, to her friends, they all doted on this girl. Meanwhile, she, the real rich daughter, was schemed against. After being disfigured, she jumped from a building and fell to her death.

Now, she returned to the moment when she was just discharged and before the tragedies happened. She lowered her head and looked at the person before her. She smirked. This time, she would control every development, and those who intended to harm her could forget about escaping.

In the history of geology, more than 500 million years ago, there was a period of the Paleozoic Era known as the Cambrian Period. This period, being the first period of the Paleozoic Era, does not only have a significant meaning for geological research, but also is the most insane, splendid and mysterious period in paleontological history.

Before the Cambrian Period, the Earth’s species were relatively monotonous. When the Cambrian Period started, just after millions of years, which is a relatively short period of time in terms of geology, all kind of species on Earth suddenly evolved wildly. Countless of invertebrates, arthropods, mollusks, brachiopods, annelids etc. have appeared on the planet without any warning, greatly enriching the diversity of the Earth’s species. This million years period is known as the “Cambrian Explosion”. And after billions of evolutionary years, the Earth today blooms with diverse lives.

The cause of the Cambrian Explosion is a huge mystery and also the biggest paradox of Darwin’s theory of evolution.

What if… the Cambrian Period is coming back in this era when human civilization has already conquest the entire planet, and the global species will once again evolve wildly, what kind of challenge will this planet encounter? What kind of fate will humans, who are falling from the top of the food chain, face?

- Description from Novelupdates

Seven billion humans living on the Earth time-traveled together after they had woken up one morning. They all heard a synthesized female voice.