Since life first appeared on Earth, the size of the largest organisms increased in size by a factor of 10 quadrillion (1016 or 10,000,000,000,000,000). Two sudden bursts, each showing an organism volume increase by a factor of one million (106), account for most this growth.1 Both bursts occurred after a significant change in the quantity of oxygen in Earth’s atmosphere. The latter oxygenation event occurred just prior to the Cambrian explosion. Research into the timing and stability of the first oxygenation event provides more evidence supporting RTB’s creation model, which predicts that complex life would appear suddenly and early in Earth’s history.
Timing of First Oxygenation Event
The geological column records the history of how life changed as time progressed. A number of geological signatures indicate oxygen appeared as a permanent component in Earth’s atmosphere 2.4 billion years ago. However, evidence shows that photosynthetic organisms arrived on the scene at least 100 million years earlier. Studies of nitrogen cycling may explain the delay.2
The presence of oxygen affects how nitrogen interacts with its environment. Lacking oxygen, a specific ratio of nitrogen isotopes is deposited on the ocean floor. Adding oxygen to the mix will increase the amount of heavier nitrogen (15N) compared to lighter nitrogen (14N and 13N). Around 2.7 billion years ago, the amount of heavier nitrogen increased by a detectable amount, providing evidence that photosynthetic organisms were producing oxygen.
A second increase 150 million years later indicates that the nitrogen cycle changed again, thus demonstrating some instability. During this latter increase the amount of “fixed” nitrogen decreased. Many organisms cannot use atmospheric nitrogen (N2) for energy production but rely on “fixed” nitrogen, primarily in the form of ammonia. The lack of fixed nitrogen then limits the productivity of the photosynthetic organisms, keeping the amount of oxygen in the atmosphere low.
This research highlights how difficult it is to effect major changes in a planet’s atmospheric chemistry. Even with the advent of oxygen producing organisms, a permanent component of atmospheric oxygen was delayed hundreds of millions of years––suggesting that the agent of change was beyond natural.
Stability of First Oxygenation Event
Most geological signatures point to the arrival of eukaryotes (animals, plants, fungi) on Earth around 1.6–2.1 billion years ago. In contrast to the prokaryotes (bacteria, archaea) dating back to 3.8 billion years, eukaryotes exhibit far more internal structure and can grow much larger. It was the advent of eukaryotes that accounts for the first rapid increase of organism size.
Even though a growing body of evidence shows that Earth’s atmosphere contained oxygen starting 2.4 billion years ago, more detailed studies hint at instabilities during its initial stages.3 This instability may explain why the first dramatic increase in organism size and complexity did not occur for roughly half-a-billion years after the first appearance of oxygen.
Evidence for this atmospheric oxygen instability comes from the same element that makes (old) bumpers shine and steel stainless, namely chromium. In an atmosphere without oxygen, chromium remains locked in the continental crust. In the presence of oxygen, chemical reactions extract chromium and lead to weathering processes that then transport it to the ocean. Additionally, these processes alter chromium’s isotopic composition in a way that can be used to trace the presence of oxygen in the atmosphere.
A team of scientists analyzed these chromium isotopes in ancient sea sediments. Their research revealed chromium isotope fractionation in formations deposited before the great oxygenation event around 2.4 billion years ago. This find indicates that the oxygen levels rose for a geologically brief period of time (a couple million years). However, in more recent formations, around 1.9 billion years ago, no fractionation occurs, pointing to a lack of oxygen in Earth’s atmosphere. Over the next hundred million years atmospheric oxygen permanently increased, preceding the appearance of eukaryotic life and the associated factor of a million jump in body size.
If naturalistic processes triggered the formation of the more complex eukaryotic life, scientists would expect to see some fossil traces of eukaryotes during the earlier increases in oxygen. Instead, eukaryotes don’t appear until oxygen gains a permanent foothold in the atmosphere. This exquisite timing is consistent with the notion of a carefully designed plan to bring about a planet maximized for human habitability.