What Was Mars Like 100 Million Years Ago? A Journey Through Time to Before It Became the "Red Planet"

The video begins by reviewing conditions on present-day Mars. Mars is said to have the most Earth-like environment of any planet in the solar system, yet it is still so harsh that an unprotected human would die almost immediately. Atmospheric pressure is less than 1% of Earth's, and the atmosphere is mostly carbon dioxide. Temperatures reach only about 20° at most. The radiation reaching the surface is thought to be at a level that almost no living thing could withstand for long. For these reasons, the video describes present-day Mars as a "dead planet," at least as far as its surface is concerned.

The first destination is Mars 100 million years ago, when giant dinosaurs roamed the Earth. According to the video, if you landed on Mars in this era, you would see a red planet not much different from today's. At the time, oceans covered a larger area of Earth than they do now, but Mars had nothing that could be called an ocean.

Still, the video points out a few differences from the present. One is Olympus Mons. The largest volcano in the solar system, it stands well over 20 km tall. It is thought to be inactive today, but small-scale activity is believed to have still been going on 100 million years ago.

The other is liquid water. Liquid water cannot last long on the Martian surface, but extremely salty water may be able to exist for short periods. Martian soil widely contains several types of perchlorates. Calcium perchlorate in particular strongly lowers the freezing point of water, and depending on its concentration, it is known to keep water from freezing even at around -75°. Traces that look as if liquid water once flowed have been found on the surface of present-day Mars, and it has been suggested that these may have been made by short-lived, highly salty water. The video cautions, however, that no conclusion has yet been reached on whether such phenomena actually occur on Mars today.

What about 100 million years ago? The video introduces a study of meteorites that came from Mars. The study reported finding minerals altered by liquid water within the last 170 million years. Based on this result, the video speculates that on Mars 100 million years ago, you might have been able to glimpse a fleeting amount of liquid water, like a mirage in the desert. Even so, its conclusion is that the planet as a whole was not very different from today.

Mars once had large oceans. With this in mind, the video travels further back in time. But Mars 2 to 3 billion years ago, it says, was still a dead planet. Atmospheric pressure was nearly the same as it is now, and liquid water could not remain on the surface for long. There was no trace of the vast oceans of the past.

Surprisingly, the video says, it has become clear that large-scale floods occasionally occurred in this era. Large amounts of liquid water are thought to have been locked away not on the surface but deep underground, and volcanic activity severely disrupted the surface layers that held this water in. A small amount of water might evaporate instantly, but a large amount does not. So, the video explains, floods swept across the Martian surface, if only for short periods.

The video conveys the scale of these floods in numbers. The Amazon River on Earth has a maximum flow of about 300,000 cubic meters per second, while the floods on Mars are thought to have reached as much as 1 billion cubic meters per second, more than 3,000 times that of the Amazon. The video jokes that if you got caught up in one, you might have the rare experience of drowning on a planet that supposedly has no liquid water.

Going back further to 3.7 to 4.3 billion years ago, a completely different scene unfolds. Mars at this time is thought to have had a vast ocean covering almost the entire northern hemisphere. At its deepest, it reportedly reached more than 1.6 km. The video says there may have been three blue planets in the solar system, with Venus and Earth.

Mars in this era may have had an Earth-like environment. A study cited in the video argues that Mars 4 billion years ago had an atmosphere of at least 0.5 atmospheres or more. The video's view is that with a greenhouse effect from carbon dioxide and other gases, Mars could have kept liquid water despite its distance from the Sun, and may even have harbored life.

Even so, the video says, it was decided from the start that Mars would follow a different fate from Earth. The cause it points to is the solar wind. Every planet is constantly exposed to the solar wind released by the Sun. The solar wind consists of electrically charged protons and electrons flying at high speed. When these particles collide with atmospheric molecules high above Mars, energy is transferred to the molecules. As a result, the molecules break free of Martian gravity and escape into space.

According to the video's explanation, this process continued for hundreds of millions of years, and the atmosphere gradually thinned. Eventually, pressure dropped so low that liquid water could no longer remain stable on the surface. The ocean water then evaporated, ice began turning directly into water vapor, and the atmosphere came to contain large amounts of water vapor. When ultraviolet light strikes water vapor, it can split into oxygen and hydrogen. Mars's gravity cannot hold on to hydrogen, so the hydrogen also leaks out into space. Once this happens, the video explains, the water can never return to Mars. The remaining oxygen reacted with iron in the soil, creating that reddish-brown rust. The video says the transformation from a blue planet to a red one is thought to have progressed gradually from about 3.9 billion to 3 billion years ago.

Earth did not lose its oceans. The video attributes this to its magnetic field. The magnetic field bends the path of the solar wind, preventing the atmosphere from being lost. Mars once had a magnetic field as well, but it is thought to have shut down completely about 3.9 billion years ago.

Here the video notes that the conditions required for a planet to have a magnetic field are actually not well understood. It then presents the following explanation as the view of many scientists. For a magnetic field to exist, a planet's core must be made of liquid metal. In addition, convection driven by the temperature difference between the inner and outer parts of the core is necessary.

Earth's core consists of a solid inner core and a liquid outer core. The inner core is growing outward from the center as the liquid metal of the outer core cools and solidifies from the inside. In the process, lighter components are pushed out into the outer core, creating buoyancy and driving vigorous convection. This convection is thought to generate electric currents that sustain Earth's magnetic field.

Mars, on the other hand, suffered several overlapping misfortunes, the video explains. First, Mars is small. Its diameter is about half of Earth's, and its mass only about one-tenth. Small objects cool faster than large ones, so the Martian core cooled early, making convection less likely.

Second, it is known that the Martian core is surrounded by a thin liquid layer made of silicon and other materials. This layer is thought to have wrapped the core like a blanket, reducing the temperature difference between its outer and inner parts. Because of these factors, the Martian magnetic field shut down only a few hundred million years after it formed. The video's explanation is that this is what produced the red planet we see today.

The video says that Mars once certainly had vast oceans, and that it is quite possible life emerged there just as it did on Earth. But on an astronomical timescale, that was only a fleeting illusion, and by losing its magnetic field, Mars lost both its atmosphere and its water. The video adds that Earth, too, is thought to lose its water to the expanding Sun billions of years from now and become a dead planet just like Mars. On the timescale of the universe, neither blue planets nor red planets last forever. The video closes on this note, ending with the hope that humanity will be able to escape Earth as soon as possible.