What would have happened if the big collision hadn't happened? If there were no moon shining on us in the starry sky, would life on earth be as full of vitality and diversity as it is today? Will humans exist?
Without the moon, the earth would be a completely different place. At that time, due to the rapid rotation of the earth, it only lasted about 5 hours a day, but now it can last for 24 hours under the interaction of the gravity of the earth and the moon. Faster rotation will also produce strong winds. When the wind speed reaches 200 miles per hour (mph), it will sweep across the earth's surface, and more violent storms will wreak havoc in the sky. Without the stability of the moon, the inclination of the earth will swing, thus losing the regular and fairly constant climate and season. This swing will make the temperature of the earth unstable, and different areas will be heated and frozen continuously. Similarly, the tides will be greatly reduced, leaving only the tides caused by the sun. However, we believe that even under such extreme conditions, there may be some life that can withstand extreme temperatures, strong winds, small tides and short rotation periods.
In any case, these life forms are more likely to be very different from what we see today. Evolution is a long process, and the slightest change in the environment can significantly change its process, which may lead to the emergence of strange species almost like alien creatures.
Bacteria can adapt to environmental changes quickly, but complex life forms like humans will be difficult because they may not have enough time to evolve and survive in drastic and harsh environmental changes. But if complex creatures can really find a way to survive on dangerous surfaces, evolution may prefer those short and chubby creatures, because if they stand too high, they will find it difficult to resist extreme winds. The continuous hurricane environment will be very noisy, and creatures need to communicate in some different ways, such as color changes or some body language.
They may use strong winds as a way to travel, and adaptation may make them grow some wings to glide in the air. Plants will also struggle in strong winds and heavy rains. They must grow very low and have long roots to ensure that they will not be uprooted. Jungles and forests with a large number of animals will no longer exist, which means that creatures can't live in trees or hide in dense vegetation to avoid storms. Obviously, we have no way of knowing what might have happened. Life may never flash, or we may have found a perfect way to adapt to the moon-like earth that we regard as hell. But we are lucky enough that a giant the size of Mars really collided with the earth, which finally gave us an environment where life can multiply on the whole planet.
Mars is the fourth closest planet to the sun and the second smallest planet in the solar system, only bigger than Mercury. In English, Mars is given the name of Roman God of War, and is usually called "Red Planet". The latter means that the influence of iron oxide, which is ubiquitous on the surface of Mars, makes Mars present a very unique red appearance among celestial bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, and its surface features are reminiscent of craters on the surface of the moon and valleys, deserts and polar ice sheets on the earth.
The thin dust red atmosphere of Mars seen from space. The lower left corner is the Algiers Plain.