The Earliest Animal on Earth?

It’s believed that life has existed on Earth for billions of years — most of that time as single-celled organisms. When did more complex metazoans or animals emerge?

It was long assumed the Cambrian explosion ushered in complex modern animals some 541 million years ago. That’s when critters like trilobites suddenly blossomed on the pages of sedimentary rocks. But then scientists found a whole suite of weird creatures even more ancient than those trilobites. These are the creatures of the Precambrian Ediacaran Period that began some 635 million years ago. They remain enigmatic, resembling sea pens, jellyfish and blobs. Were they plants? True animals? Or did they represent some failed evolutionary experiment that went nowhere? The current consensus is that some were true metazoans.

Now, in the journal Nature, at least one scientist is saying, “Forget the Ediacarans!” There may be evidence of fossil sponges dated at 890 million years old! If so, that would make them the oldest complex animals discovered to date. The fossils in question, consisting of crystalline tube-like structures, are microscopic and were discovered in the Northwestern Territories of Canada by sedimentary geologist Elizabeth Turner (Laurentian University, Canada). They were found in association with ancient reef-like structures known as stromatolites that were left by photosynthetic bacteria.

While some paleontologists find Turner’s paper convincing, others ask for more evidence. For instance, Rachel

Wood (University of Edinburgh, UK) says that the branching tube-like patterns shown in Turner’s paper don’t necessarily indicate an ancient sponge. They could be patterns left by simpler microbes or even inorganic crystals.

With an initial line of evidence now drawn, the debate is engaged. Here’s to exploring even deeper into the history of complex life on Earth!

Within our solar system, three neighboring planets attract particular attention — Earth, Venus and Mars. While these three rocky planets should be similar, given their similarities in orbit and other regards, they are surprisingly quite different. A recent probe to Mars is showing just how different that planet is from our own.

Mars also has earthquakes, “marsquakes,” if you will. Most register low — below magnitude 4.0 — compared to earthquakes. Without proper instrumentation, scientists were unable to draw conclusions about the deep interior of Mars. But that changed in November 2018 with the arrival of NASA’s InSight (Interior Exploration using Seismic Investigation, Geodesy and Heat Transport) mission that brought a suite of geophysical instruments to the Martian surface. Now, for the first time, we have direct seismic observations from another rocky planet that we can compare against what we know from intensive studies on Earth.

Three articles in the July 23, 2021, issue of the journal Science explore the evidence that has been sent from InSight. It turns out that the ironnickel core of Mars is larger than previously thought. The boundary of the core exists about midway down into the planet, or a depth of around 970 miles. The core also seems to be less dense than expected, with the iron-nickel elements combined with lighter elements like sulfur.

While there had been debates about whether the Martian core had solidified or not, it seems to still be in a liquid state. But, with a relatively thin mantle, that liquid state has not maintained the heat necessary to drive a so-called geodynamo needed to maintain a strong magnetic field on Mars. On Earth, our magnetic field not only creates wonderful spectacles such as the Northern and Southern Lights it also protects us from solar radiation from the Sun. It seems Mars once had a similar geodynamo but its interior cooled far more quickly than Earth’s, resulting in the loss of a strong magnetic field.

Scientists hope to continue monitoring marsquakes for two more years, so watch for greater refinement in findings and a more detailed picture of the interior of Mars and how it compares to Earth.