探索世界之寻访外星人 Alien Neighbors 5

Understanding how life got going on our own planet will help us target where we look for it in space, both within the solar system and beyond.

Biophysicist, David Deamer, studies tide pools. A tide pool has the right mix of conditions for the formation of the first simple organisms. "If we think about the kinds of key events that might have been part of the beginning of life, certainly one of them had to be a sufficiently concentrated solution. Life could not have begun in a highly dilute solution of molecules because they can't find each other, molecules wander all over the place. The only way they can react is if they bump into one another. So, this means that there must have been a concentrating mechanism. Tide pools are an obvious concentrating mechanism because as a tide pool dries out, everything in it gets more concentrated. "

In his lab, Dr. Deamer wants to see how the first microorganism might have sprung up under similar conditions. "Imagine the tide has gone out, and the pool is drying up, and leaving behind a thin film of organic material. "

Simple organic material likely to have been on earth before life began. "The tide comes back in." The incoming tide churns the matter together. Ultraviolet light, like the sun, adds a heat source. With the agitation and higher temperatures, something begins to happen. Some of the molecules have formed bubbles and another kind of molecule has become trapped inside the bubbles, mimicking a cell and its nucleus. Although not actually a living thing, this simple structure mimics a single-celled organism that could have sprung up under similar conditions.

Yellow Stone Park, like a reminder of early earth, it has steaming lakes and hot mud pools that erupt at burning temperatures. A much less forgiving environment than a tide pool, yet here, against all expectations, life has taken hold. Some microorganisms are being fossilized as quickly as they form.

Dr. Jack Farmer, one of NASA's exobiologists, if he can understand how simple life forms become fossilized here on earth, space fossils may one day be easier to spot.

"What I'm interested in, in an environment like this, is how organisms are captured during the process of mineralization that occurs and turn into fossils. And, the idea is that the rates at which these minerals are forming is so fast that the organisms don't even have a chance to die before they become entrapped in the minerals. And, that means that you capture a lot of biological information mostly as different types of fabrics in the rock. So this is a really excellent place to look for microbial fossil information. "

The hot conditions at Yellow Stone are almost like early earth, but not quite. There's too much oxygen.

When life started on this planet, there wasn't any free oxygen in the atmosphere, there was obviously oxygen, in the world, but it was bound oxygen, it wasn't free oxygen. So all the oxygen in the air has come from green plants.



words in this passage:

dilute solution :稀溶液

churn : shake or agitate with violent motion 搅拌

agitation:搅动

mimic: to copy the way in which a particular person usually speaks and moves, usually in order to amuse people:模仿（NOTE：mimicking, mimicked, mimicked）