Origins of Life on Earth & Beyond
Origins of Life on Earth & Beyond --Harvard Research Reveals New Discoveries[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]
Two of the world's preeminent scientists, Harvard astronomer Dimitar Sasselov and Jack Szostak, a Nobel Prize-winning professor of genetics at Harvard Medical School, co-founded the Harvard Origins of Life Initiative --an interdisciplinary center unlike any other in the world. It studies everything from planet formation and detection to the origin and early evolution of life.
The focus of Szostak's lab is to understand how life, which depends on self-replication and Darwinian evolution, emerges from chemistry. For decades, scientists have tried to understand the basics of life by taking existing life and attempting to trace it back to its origins. But their experiments all failed. In the past decade, Origins researchers began to try building it from scratch.
A giant step toward solving this puzzle of how life was started on Earth was taken in the 1980's with the Nobel Prize–winning discovery by Tom Cech and Sidney Altman that RNA, the sister molecule of DNA, can catalyze certain chemical reactions inside cells, a job previously thought to be the exclusive domain of proteins. Until their discovery, RNA was thought to have just one function: storing the genetic information cells need to build proteins.
This new revelation about RNA's dual role suggested to some scientists, including Harvard's Szostak, that RNA likely existed long before DNA or proteins because it might be able to catalyze its own reproduction. Their discovery made it easier to think about how life began, Szostak says. "They inspired me to try to think of ways to make RNAs in the lab that could catalyze their own replication."
Szostak and his team is working to recreate a hypothetical model of this process in the laboratory. By building simple cell-like structures in a test tube, they are attempting to establish a plausible path that led primitive cells to emerge from simple chemicals. Ultimately, Szostak hopes to answer fundamental questions about evolution's earliest steps.
Building on earlier work by other scientists, Szostak and colleagues began experimenting with a clay mixture common on early Earth called montmorillonite, which was found to catalyze the chemical reactions needed to make RNA.
So, did life originally spring from clay as some creation myths assert? Not necessarily, but it does provide a possible mechanism for explaining how life initially arose from nonliving molecules. Szostak's team at the Howard Hughes Medical Institute and Massachusetts General Hospital showed that the presence of clay aids naturally occurring reactions that result in the formation of fatty sacks called vesicles, similar to what scientists expect the first living cells to have looked like. Further, the clay helps RNA form. The RNA can stick to the clay and move with it into the vesicles. This provides a method for RNA's critical genetic information to move inside a primitive cell.
"It's exciting because we know that a particular clay mineral helps with the assembly of RNA," Szostak said. "There certainly would have been lots of environments on early Earth with clay minerals. It's something that forms relatively easily as rocks weather."
The researchers also found that the clay expedited the process by which fatty acids form vesicles that could serve as cell membranes. When RNA and fatty acids were mixed with the montmorillonite, the clay seemed to help transport the RNA inside the vesicles, forming a cell-like structure. Szostak and his team surmised that a similar process could possibly have led to the creation of the first cell.
Szostak first showed how a simple membrane could form from clay available on the early Earth. More recently, he and others have been searching for a simple series of steps that can explain how primitive genetic material replicated itself.
If they succeed, "then, since we know there are probably hundreds of millions of Earth-like planets in our galaxy alone, it would make it seem pretty darn likely that there's life in other places out there," he says.
If lab experiments show that the process of turning chemistry into life is extremely complicated or unlikely to have happened, "then it would be possible that maybe life only started here. Maybe there's only life on Earth."
Prof Szostak and the other Origins researchers say they are nowhere near actually creating life, so they don't think their work poses any ethical concerns. Lawrence Krauss, a physicist who leads the Origins Project at Arizona State University, says trying to figure out how the universe came from nothing doesn't tread on religious ground, either - at least no more than Copernicus and Darwin did.
"Many people say it's a religious question, but I've been trying to say it's a scientific one," says Prof Krauss, whose book on the subject, A Universe from Nothing, is due out in January.
"Detecting alien life in the form of an HIV virus in the human patient is not much different than detecting alien life" on another planet, says Steven Benner, a distinguished fellow with the Foundation for Applied Molecular Evolution in Florida, which is searching for alien life forms on Saturn's moon Titan, as well as developing test kits for HIV and hepatitis.
If Sasselov and Shostak succeeed in their goal, maybe one day we "could gaze at the sky and know that a place somewhat like home exists around "THAT" star, where life might be gaining a toehold somewhere along the long and precarious evolutionary process that led, on Earth, to humankind. And perhaps it is staring back at us!"