In the Cambrian Period, 540 million years ago, the supercontinent Gondwana was still straddling the southern hemisphere, and the two fragmented continents where Lauia and present-day China are located floated in the oceans of the northern hemisphere, doing nothing — there were no animals or plants, and the land was desolate and lifeless, and it was hard to imagine what it would be like.
Although the algae in the ocean are prosperous and bloom everywhere, there are no animals, only simple creatures such as trilobites and jellyfish, and life on the earth is desolate and lifeless.
However, one day in a certain month of a certain year, a small comet suddenly roared into the atmosphere, burning with flames, and soon exploded in the air, and countless fragments splashed into the ocean. Things are very ordinary, the earth was more likely to be hit by meteorites at that time, and it was not afraid to smash the flowers and grasses, and there were no flowers and grasses anyway.
Curiously, however, after this humble event, a large number of creatures mysteriously appeared on earth in a short period of time, and almost all animal phylums, including the phylum Chordate, where humans are located, were born during this period, which scientists call the Cambrian explosion of life.
Of course, this comet impact event is just speculation, and we don't know exactly what happened at that time.
In 2018, a study published in the journal Advances in Biophysics and Molecular Biology speculated that the comet was likely carrying a small piece of extraterrestrial organic material, a retrovirus, splashing in our oceans and beginning to reprogram life on Earth, leading to a short explosion of life, with the sudden emergence of many new animal phyla in the oceans.
Carrying these alien viruses are likely the eggs of cephalopod mollusks such as octopuses, frozen in the cold ice of comets and flown in space for millions of years.
So we all have the potential to be descendants of extraterrestrial beings, and these extraterrestrial beings are likely to be mollusks like octopuses, because they can regularly do a lot of high-level RNA editing on their own to change themselves and adapt to changes in the environment as quickly as possible.
Of course these are more of a guess, everything is just possible, including the comet.
Scientists have indeed found fossil evidence of suspected microorganisms in some meteorites, indeed detected life-carrying particles suspected to come from outer space in the upper atmosphere, and indeed found that octopuses can do a lot of RNA editing, but this is not enough to prove that our distant ancestors came from the ocean of an extraterrestrial planet, and we are aliens on our own planet.
In fact, this is another hypothesis of the origin of life on Earth - panspecies, also known as germ theory, this hypothesis speculates that various forms of microorganisms exist widely throughout the universe, and through meteors, asteroids and comets spread, looking for suitable planets to multiply.
Francis Crick, winner of the 1962 Nobel Prize in Physiology and Medicine, and another scientist, Leslie Ogogen, took this hypothesis to a new level, proposing the ideographic panspecies that the spread of life in the universe did not occur spontaneously, but was deliberately done by advanced alien civilizations.
Crick even claimed that life on Earth was unlikely to originate on Earth.
If so, of course, we are not a lonely being in the universe, and as long as there is a planet with water, it is possible to evolve life — and if we can really find traces of life on Mars, this hypothesis may be corrected.
So the Cambrian explosion of life is still very mysterious, and we still can't explain why so many lives suddenly appear, everything is possible.