Mars. A distant dark red desert reflects the old decadence of this land. It lost its life early, the crust stopped roaring, and the volcano was extinguished. The barren soil cannot be infiltrated by a drop of water, and the endless Gobi cannot see a trace of life. The never-ending wind and dust whistled, rolled up the sand, and danced like a puppet in the faint sunlight. It was a desolate land, but there was a traveler slowly advancing.
Selfie on Curiosity on May 12, 2019 | NASA/JPL-Caltech/MSSS
It is a human creation, Curiosity, a rover. It travels to the far ends of the unknown land, looking for the lost story of the land.
On July 9, it sent a picture back to its home planet. The protagonist of the photograph is ordinary: a stone about the width of a person's shoulder, earthy yellow, covered with fine layers of grain. Such a stone may not be put on Earth and no one will look at it more, but NASA scientists are particularly interested in it.
It was such an inconspicuous stone that allowed them to see an ancient lake, to see the sparkling waves and pulsating waters of the past; and it was even possible that in such a lost paradise, ancient life was once conceived.
Martian sedimentary rock | photographed by Curiosity's mast camera NASA/JPL-Caltech/MSSS
Curiosity walked into "Mud Bay"
In 2011, Curiosity was launched, landing on Gale Crator on Mars. In this crater, there is a "clay-rich area". As the name suggests, the surface of the strip is rich in clay minerals (on Earth, commonly known as mud). In recent months, Curiosity has been slowly driving here. The exposed rocks of the clay zone provide it with an excellent opportunity to observe the details of the composition of the earth's crust in the region.
On July 9 and 10, Curiosity took close-ups of the textured rock with its "eyes" (mast camera, Mastcam, mainly used to patrol the foreground) and "handheld camera" (Mars handheld lens imager, MAHLI, Mars Hand Lens Imager, fixed on Curiosity's robotic arm, which can be shot at a low angle at close range). Based on human experience in conducting geological research on Earth, it's almost certain — it's the remains of a giant Martian lake.
A close-up of the sedimentary layer taken by Curiosity's "handheld camera" | NASA/JPL-Caltech/MSSS
Sedimentary Rocks – A history book of ancient environments
The remains of the lake can be seen by looking at a single stone, first and foremost because it is a sedimentary rock, and the sedimentary rock has the function of accurately indicating the paleoenvironment.
Just as biologists classify the vast number of life on Earth into categories such as "animals," "plants," and "fungi," geologists classify rocks on Earth into the three largest orders: igneous, sedimentary, and metamorphic.
Formed by the direct solidification of piping hot magma, it is igneous rocks; it is formed by the consolidation of sand and gravel debris accumulated on the surface; when these two types of rocks are buried in the earth's crust for a long time, so that the composition changes, metamorphic rocks are formed.
Rocks are not only present on Earth, but also on any terrestrial planet (such as Mars, Venus, Titan, etc.), and even many asteroids, which are also made of rocks, but most of them are igneous. Sedimentary and metamorphic rocks are difficult to form.
Sedimentary rocks are the products of compaction consolidation such as gravel, sand, powder, ash, mud, etc. If you want these things to appear on the surface of a planet, you can't do without a premise: that is, there must be an atmosphere and water flow on its surface, which can wear and destroy the rocks on the surface of the planet for a long time. In addition, they also take on the role of porters, piling up these broken debris, burying them little by little, and eventually consolidating into rock. So, the presence of sedimentary rocks on a planet's surface can at least indicate that the planet had an atmosphere and water flow during the historical period of rock formation.
So, how does the atmosphere blow? What does the water flow form on the surface? Are they rivers or vast lakes and seas? At this time, the sedimentary rock will use its accumulation method, use the special texture structure it has accumulated, and use its layer thickness and particle size to faithfully reflect all this.
On Earth, such sedimentary rocks are not uncommon | wikipedia
This correspondence is very precise. The reason why scientists believe that the Martian rock found this time is the product of an ancient lake is because the sedimentary characteristics of this rock can only be explained in the unique hydrodynamic parameters of the lake.
It is made of layers of delicate grain. Just as the rings of trees gradually increase over time, the sediments on the surface of the Earth's crust will be stacked layer by layer over time, eventually forming a continuous strata (Strata). The thickness of the formation, the size of the sediment particle size of each set of grained layers, all of these parameters, are related to the energy of the water flow.
When the sediment particles in a layer are large, it indicates that the water flow carrying them is very energetic (otherwise it cannot be moved). The sludge-based strata are often formed by slowly settling under calm weak water dynamic conditions (the water flow is so weak that even the sand cannot be moved, only the suspended muddy water slowly settles).
In addition to the composition, the texture of the formation itself also reflects the current conditions at that time - when the water body is particularly quiet and cannot be stirred by strong winds and waves, a delicate horizontal layer will be left in the rock; in the environment where the waves are frequently stirred, the formation will leave a huge interlaced layer.
The center of a large lake often has an important feature: the closer to the center of the lake, the calmer the sedimentary environment at the bottom of the lake bed (because of the depth, the waves on the surface of the water are not reached), which is conducive to the deposition of delicate and uniform layers; and in other surface water bodies such as lake shores and rivers, the churning energy of the waves has either been stronger, or strong and weak, and will not precipitate such a delicate and stable horizontal layer like the center of the great lake.
Finding an ancient Martian lake is exciting enough, but scientists are expecting more. In fact, from the beginning, the Gale Crater was set as the landing site, indicating that Curiosity's trip must be an important mission. Whether it was in previous years when it was grinding on the surface of the rock, or today it pays special attention to the ruins of the Great Lakes, it is still a planning node on the final main line. This main line constitutes the ultimate question of human beings on Mars - whether there has ever been life here.
The remains of ancient lakes are naturally the best place to explore ancient life.
Deep and calm, the depths of the great lake have always been an excellent environment for the burial and deposition of organisms| wikipedia
Deep Lakes – a museum of fossils
At least on Earth. Whether it is the existing large lakes today or the lacustrological sediments of hundreds of millions of years ago, countless eloquent examples show that deep lakes may not be the most prosperous places for life activity, but they are definitely the most ideal resting places after the death of living things.
In order for an environment to have a large number of organisms to reproduce, the premise is to have excellent conditions for survival. But the area where organisms flourish is not necessarily an area conducive to fossil preservation.
For aquatic organisms, these "blessed places of survival" tend to have shallow and clean water bodies (translucent, contribute to photosynthesis, and form the basis of the ecological chain), and turbulent water flows (help to provide "living water" and frequently transport dissolved oxygen and nutrients). These living times can "turn the sky upside down" paradise, and it is not an ideal burial place. Oxygen-rich water bodies, active ecological chains, and turbulent water flows cannot make the remains of organisms stable, let alone stably buried for millions or even billions of years and eventually become fossils.
If the organism wants to be buried, it probably needs to meet such conditions: the environment is quiet enough (to avoid the disturbance of water erosion), the chemical reaction is not active (to avoid oxidation), and to bury as soon as possible (to avoid environmental changes, long nights and dreams). Taking these factors into account, settlement centers for large waters (e.g., the center of a large lake, a deep trough on the continental shelf) tend to be the best burial sites. If you look at the well-known fossil strata on Earth, you will know that from the pencilstone creatures with rich structural details in the Southwest Silurian Longmaxi Formation to the vivid and even hairy Chinese dragon birds in the Rehe biota of the Mesozoic Era in North China, which do not meet such burial conditions.
In delicate sedimentary rocks such as shale and marl, there are often fossils that are well preserved and rich in detail. Is this true of Earth, and is it also true of Mars? | fossilmuseum
The same is true of these principles on another planet. As long as (even the most primitive) life has ever appeared on Mars, the center of the ancient Great Lake provides the most suitable environment for them to bury. Once you have survived, you will eventually leave an imprint. When the faint sunlight and the wet surface are sleeping in history, when the short golden age becomes the dry and desolate rocky mountains of later generations, this sleeping alien world still has the opportunity to see the sky again.
Perhaps, the evidence of the existence of life is hidden in this thousand-layer cake-like stone that Curiosity recently studied!
You see, in the yellow sand of the earth, a lifeless machine is trying to find the remnants of the existence of life. The impact of this picture is no less than the stark contrast between the red desert and the blue deep sea, but it may be the best footnote to the story of today's solar system.
Author: Tracing Eagle
Edit: Steed
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