Hydrothermal vent along the Mid-Atlantic Ridge. Such places are believed to have held the required chemistry to form Earth’s early life.
Photo: Wikimedia
By Kevin McKeon, Maine Master Naturalist
While walking around Sanford’s trails, bathing in nature’s wonder, we’re surrounded by all kinds of life, made from all kinds of stuff, which is made up of all kinds of tiny biological cells. And in these cells, there’s this stuff called ATP, adenosine triphosphate, which is found in every cell of every living thing. You’ve probably never heard of it, but it’s important, so let’s explore it a bit.
Life has been on Earth for at least 3.7 billion years, and science has shown that its birth could very well have been near thermal vents in Earth’s oceans. These hot areas, discovered in 1977 by Woods Hole Oceanographic Institution scientists, are formed by magma extruding from Earth’s crust, then mixing with cold ocean waters. About 240 vents have been documented, but close to 1,200 are thought to be peppered along various oceanic ridges and tectonic plates. The magma/water mixing produces both temperatures reaching 660ºF, and alkaline pH levels containing phosphate-based molecules. It’s believed that early-Earth’s ocean with its high acidic levels clashed with the thermal vents’ alkaline levels, creating a form of energy at a molecular level called a proton gradient that enabled emergence of life-functions for the earliest cellular life. These conditions at the vents provided an ion exchange process, chemiosmosis, to allow the spontaneous formation of organic molecular cells, or protocells, that learned to replicate. Scientific theories propose that fats began covering these cells, eventually evolving into the first true cells.
As the electrons from mineral atoms and molecules bounced around among Earth’s early oceanic cells, new molecules were formed. But more importantly, cells haphazardly began to combine with other cells, forming new substances. One of these new molecules was ATP. Turns out, ATP became the substance that stores and supplies the energy that every living cell needs to exist. But back on primordial Earth, the formation and cellular use of ATP was limited to the amount needed for simple cellular maintenance, so cellular growth was limited: It could grow a bit larger but remained a single cell — unable to replicate.
So life was the simplest of single-celled stuff swimming in Earth’s primordial ocean waters. Above these waters, Earth’s atmosphere was mostly nitrogen, carbon dioxide, water vapor, and other trace gasses — including very little oxygen. This made early life an anaerobic process (lacking oxygen), and living cells got their energy from the ocean’s dissolved minerals as they passed through the cells’ membranes. So, without oxygen available to fuel higher energy levels, life on Earth was pretty much single-celled stuff.
Then, about 2.4 billion years ago, some of these primitive cells began making much more ATP by doing photosynthesis — which, as we know, creates oxygen. For the next several hundred million years, these new photosynthetic cells expelled huge amounts of oxygen into Earth’s atmosphere, creating an atmospheric oxygen level of about 2%. This became known as The Great Oxygenation Event. While 2% doesn’t sound like much (it’s 21% today), as that oxygen combined with other atmospheric gasses — effectively “thickening” the air — Earth’s atmosphere began reflecting increasing amounts of solar heat from the sun away from Earth, causing temperatures to plunge. Some 500 million years later, Earth entered its first Snowball Earth ice age, freezing over from pole to pole.
Estimates vary, but after about 25-50 million years of the Snowball Earth era, powerful volcanic activities began spewing gasses into the atmosphere, erupting through several miles of ice, altering Earth’s greenhouse gasses enough to eventually warm the planet. Two great leaps of evolution then happened. First, about 1.7 billion years ago, cells decided to eat other cells. But some of the eaten cells kept living inside the predator cells — effectively forming a new, more complex cell — and the swallowed cell eventually evolved the responsibility of making a lot of ATP for its host cell. Secondly, about half a billion years later, the eaten cell evolved into a primitive form of photosynthesizing bacteria, which eventually evolved into a chloroplast — the part of a cell that does food-making for plants. These two cellular combinations are generally considered the huge leaps of evolution responsible for all life as we know it today.
But we’re still talking about life on a tiny cellular level; where did the bigger stuff come from? Cells need phosphorus for just about everything in the cell, including ATP. And it’s the phosphorus in ATP that stores cellular energy; as the ATP breaks down, energy is released to the cell. But there wasn’t much phosphorous in Earth’s primordial soup because it was locked up in bedrock. So, here’s where Snowball Earth and many other subsequent ice ages helped out: As the advancing and retreating glacial ice ground against Earth’s bedrock, along with erosive winds and rains, a multitude of phosphorus was released into the environment, flowing to the ocean.
So, with a phosphorus-rich ocean fueling ATP formation, cells began to grow, forming cell clusters that grew. Competition for survival required the evolutionary growth of survival techniques like capture and defensive devices, elusive strategies, and locomotion, camouflaging, and reproductive mechanisms. Successful life forms grew more advanced, crawled from the oceans, and adapted to populate the lands. So here we are — back on Sanford’s trails pondering evolution, life, and now — ATP!
A few weeks ago, scientists released findings regarding the possible source for life’s building blocks at the molecular level — the stuff needed to form these early cells at the thermal vents — AND the method of delivery to Earth. We’ll take a peek at this exciting revelation next week.
The post How it All Started: Hot Magma, Cold Water appeared first on Sanford Springvale News.
