Part of the show Origin of Earth, The Moon and Life
Where did life on earth begin ? Charles Cockell joins us to explain why meteor and asteroid craters are a likely prospect.
Charles - I've been working up in the high Arctic looking at an asteroid crater formed about 30 million years ago. We have been looking at is the way life re-colonised this asteroid crater. On the early Earth 3.5 billion years ago when life first emerged, asteroid and comet impacts were much more frequent -1000 times more frequent. Asteroid and comet craters were a common habitat then. Looking at how microbes can re-colonise these impact craters gives an idea about how life might have survived on early Earth
Chris - Is your idea that destructive asteroids and comets could have spawned life?
Charles - Yes. People think of collisions as wholly destructive. But what we've found up in the Arctic is that asteroids and comets can forms little cracks in the rocks by shattering them, which essentially sets up little apartment complexes in the rocks where microbes can live. We found that rocks hit by asteroids and comets actually have more microbes in them than rocks that have not been hit. This is a very interesting example of the way in which impacts can create an impact for life rather than destroy it.
Chris - Phosphorus is relatively rare on earth, but is needed to make many biological molecules like DNA. Could a meteor that was relatively rich in phosphorus have slammed into the early earth and artificially elevated the amount of phosphorus available in that particular area?
Charles - Yes, this is one possibility. Asteroids and comets also could have been involved in the origin of life themselves because they deliver a huge amount of energy. The energy gets released into the rocks surrounding the impact crater, and it causes the ground to heat up for several thousand years, maybe even 10 thousand years. This heat can provide a source of energy for complex organic reactions to form. The great thing about asteroids and comets craters is that they are big holes in ground. Water tends to collect in holes. A hole in the ground, full of water and heat really is Darwin's proverbial warm little pond, the ideal place for complex organic molecules to form
Chris - Volcanoes produce a number of substances that are important precursors for many of the molecules involved in life. Do you think they could have been created under similar circumstances to the reactions in impact craters?
Charles - It's not just impact craters. Volcanoes could have done the same thing as well as hydrothermal vents under the ocean. Life may have been simultaneously occurring in several different places, and one place could have been the first place to give rise to an organism that eventually colonised the earth. Deep oceans, volcanoes, impact craters there's lots of energy, water interesting chemical reactions going on.
We know there are organics in space and early earth would have had them delivered. What is more controversial is whether micro-organisms were delivered from space. That doesn't really solve much because micro-organisms still would have to evolve from somewhere.
Life could have evolved on Mars. We know it had liquid water in its early history, which could have been conducive to early life. There is speculation that life on early Mars could have been transferred to Earth. W e might find evidence of this life on Earth. We know that Martian meteorites land on earth. And there are probably pieces of Earth landing on Mars. Some of those rocks might have contained micro-organisms.