Alan Stahler: Life just got older
We are all biochemists. Every moment, our bodies perform gazillions of chemical reactions, putting molecules together, taking them apart. While a chemist in the lab uses test tubes and beakers, our bodies use enzymes — tiny machines that can grasp atoms and molecules.
Some enzymes pull atoms and molecules together; others take them apart. Lactase, for instance, is the enzyme — the machine — that takes apart lactose (milk-sugar) in baby’s gut.
If we kept all the enzymes we need on-hand, all the time, our bodies would: a) be bloated with enzymes; and b) not have enough atoms left over to grow muscle and bone and brain. So we only make enzymes when we need them. We make enzymes with enzyme-making enzymes.
When mealtime is over, and baby runs out of lactose to digest, she stops making lactase (the enzyme that digests lactose), and makes enzymes — machines — to take lactase apart.
If we had to remember all the things we need to do to keep ourselves alive, we’d all be dead. It would be like having to think about each ball as you juggled a gazillion of them. We’d drop things left and right.
When Earth first formed, 4 1/2 billion years ago, it was hot enough to melt iron — nearly all of Earth’s iron flowed down, into the planet’s core. At the same time, space-rocks pummeled the planet continuously.
Heat and constant bombardment kept the Earth sterile. Slowly it cooled, and the bombardment tapered off. Liquid water no longer boiled away, but formed ponds and oceans.
If you’re going to juggle a gazillion balls, you don’t start out with all gazillion, all at once. You start with a few, then add more. This takes time. How much time did it take, once the environment became clement — maybe 4 billion years ago — how long did it take for non-living rocks and water and air to evolve into living flesh — into jugglers able to keep themselves alive?
The oldest fossilized life-forms yet found are stromatolites — colonies of sticky bacteria that grew in layers, one on top of another, to form mounds. The layers are evident when the mounds are cut in half, either by saw or by erosion; found underfoot in Glacier National Park, billion-year-old stromatolites are called “cabbage-heads.”
Until last week, the oldest cabbage-heads known were just shy of three-and-a-half billion years old, meaning that life had formed within roughly half-a-billion – five hundred million — years of Earth becoming comfortable.
Last week, in the journal Nature, Allen Nutman (University of Wollongong, New South Wales, Australia) and colleagues described what look like miniature stromatolites, more than 200 million older. If confirmed, this means life evolved even faster than we’d thought.
This is even more impressive when you realize just what the bacteria that built stromatolites could do.
Question: How long did it take us to learn to feed ourselves?
By “us,” I’m including all of life. We humans cannot feed ourselves. We know how to eat, of course, but can we make our own food? No way! We’re totally dependent on our cousins, the green plants, to harness sunlight to turn carbon dioxide and water into something they — and we — can eat.
Making food with sunlight requires a whole new set of juggling tricks, beyond just staying alive. Yet Nutman and colleagues see evidence that the single-celled critters that made their fossils could do just that – they could photosynthesize their own food. If confirmed, then an awful lot of evolutionary work must have got done in a (relatively) short amount of time.
Which, of course, raises the question: If evolution can work so quickly here on Earth, might it not work just as fast on other planets, circling other stars?
Al Stahler teaches nature classes for students of all ages, kid to adult. His science programs can be heard on KVMR-FM, and he may be reached at firstname.lastname@example.org.
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