A Warm Little Pond

Most Terrifying Moment
Boo! Did we scare you? If not – boo! Still nothing? Well then show us how it’s done. This week, write about the most terrifying moment in your life.

When we last spoke, I promised a short history of Life, the Universe, and Everything.  It seems I have only delivered an introduction to the latter two, without really talking about how Life itself came about on this majestic blue marble.  The origin of life on Earth admittedly relates only tangentially to terror and fear and yet I am still going to make the connection and write about it today.

Earthlings have had a lot to fear over the years.  Since the planet formed 4.5 billion years ago, there have been colossal meteorite impacts, extinction events, dramatic shifts in atmospheric content, ice ages, predators, and parasites (among other things) to disturb life on Earth.  Death has been looming around the corner for the inhabitants of this planet since day 1.

4.6 billion years ago, enough Hydrogen collapsed into a single area for our Sun to be born.  Baby Sun still had a ring of gas and dust known as a protoplanetary disk.  Over the next 100 million years, the gas and dust collided with itself and formed at least 8 discrete, large bodies that we now know as the planets of our solar system.  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune were not alone in our solar system at the time, however.  There were other, smaller bodies that were flying around with eccentric orbits and colliding with the larger protoplanets.  I make it sound easy and simple, but these chunks of rock and ice were travelling at incredible speeds (in the 10-100km/s range) and so wreaked tremendous havoc.  Earth collected these souvenirs of the early solar system for about 700 million years.  The barrage ended about 3.8 billion years ago and geologists call the time 4.1-3.8 billion years ago the Late Heavy Bombardment.

If you could stand on Earth 4 billion years ago, you wouldn’t recognize the place.  It was hot, extremely volcanically active, and much of the surface was molten.  The atmosphere was toxic and there was nothing green.  Remember that scene at the end of Star Wars III when Obi Wan cuts Anakin’s legs off?  Earth was like that planet, just 10x hotter and with a toxic atmosphere.  What is amazing is that within half a billion years, the Earth cooled enough for life to emerge on this terrifying exploding rock.  The earliest fossil evidence for life is a debated issue, but estimates range between 3.5 and 3 billion years old.  The oldest rocks on earth are only 4 billion years old (the rest have been recycled into the mantle)  This means that it only took 500 million years for life to flourish here.

So how, where, and why did life appear here all those years ago?  We’re not really sure.

There are some good theories though, and I will present two here tonight.

1) Panspermia

From the Greek pan (=”all”) and spermia (=”seed”), Panspermia is the idea that life on Earth is the consequence of it arriving here from somewhere else.  It sounds far-fetched at first, but read on before judging and keep in mind that the theory has some well-respected proponents including Fred Hoyle, Francis Crick, and Stephen Hawking.

Assuming there is a source for biological material (ie. another planet with life), could life survive the journey through space?  This has been a topic of intense research and while the jury is still out, there have been some interesting insights.  Creatures on Earth have been found to withstand some pretty incredible environments.  The tardigrade has survived the vacuum of space, the intense radiation of a nuclear reactor, heat, desiccation, and cold.  As long as it is able to go into its tun state, the tardigrade seems nigh invincible.  Evidence for simpler life forms has also been found in interesting, panspermia-suggesting places.  There are several instances of what appear to be bacteria found on meteorites (ALH84001 and Tatahouine) and viable bacteria were also found upon examination of the Columbia space shuttle wreckage.  The bacteria had survived the heat of re-entry as well as the explosion.

Meteorites also provide evidence for panspermia.  Many meteorites that land on Earth are categorized as carbonaceous, which (unsurprisingly) means they contain a lot of carbon.  One such meteorite, named Murchison, landed  in Australia in 1969.  Murchison contains amino acids, hydrocarbons, and carboxylic acids.  David Deamer, a researcher from UC Santa Cruz, has studied this meteorite extensively and he found that when he crushed up a sample of the meteorite and suspended the solution in water, the material self-assembled into proto-cell like structures termed micelles.

The possibility that life, even as we know it, could survive a journey through space is interesting, but the assumption made earlier (that there is a source for biological material) is a big one.  Critics of panspermia allege that the theory is just putting off the question of how life originated.  If it was delivered here, it still must have formed somewhere.

2) RNA World

In 1871, Charles Darwin famously suggested to his friend J.D. Hooker:

It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present.— But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts,—light, heat, electricity etc. present, that a protein compound was chemically formed, ready to undergo still more complex changes…

In searching for the origin of life, scientist have thought up many different warm little ponds.  Miller and Urey, in 1952, cycled water vapour through a highly reducing atmosphere and delivered periodic electric shocks.  Amino acids, one of the basic building blocks of proteins and life, were formed.  Darwin didn’t seem to have been too far off.

There are two basic requirements for the first living thing: genetic information and a way to replicate and pass it down.  For a long time scientists were stumped with a chicken-and-egg problem.  Which came first, the information or the transfer method?  An information-storage molecule can hardly be considered life if it can’t reproduce.  A reproducing cell with nothing in it is no different than a bubble splitting into two.  This problem was partially solved with the discovery of ribozymes.

Ribozymes are special RNA molecules that are able to perform both of the aforementioned tasks.  They store information in 4 nucleobases and can catalyze their own replication.  The idea is that on ancient Earth, some of these ribozymes were formed and outcompeted other molecules for space and resources.  The RNA was eventually replaced by DNA, a double-stranded, more reliable information-storage molecule, then fast forward a couple billion years and here we are!  RNA still performs crucial message delivery services in our cells and helps construct proteins, but our genes are stored in DNA.

So, did life form here, or elsewhere?  This continues to be a big question in the emerging field of astrobiology.  There is a lot to discover, but there has been some really great progress recently.

What’s so scary about that?  Imagine all the thousands of different ways that life could have been wiped out along its 3.5-billion year existence.  It is the most thrilling story ever.  Dodging hurtling rocks of death, hoping a star doesn’t explode nearby, wondering if a gamma-ray burst will wipe out everyone tomorrow, running away from T-Rex, life on Earth is an epic tale of fortune, despair, glory, and discovery.  I am glad to be a part of it.

If you are interested in this sort of stuff, I recommend watching this video.  It is a lecture by David Deamer presented at McMaster University in 2005.  Also, visit NASA’s Astrobiolgy website for all the latest news.