On a more fun note, here's a pretty X-ray image of a very old rock (3.22-billion-year-old Moodies sandstone from South Africa). Red=Fe, green=Ca, blue=Mn, white=Mn, cyan=K.

I've been asked a few times over the last few days what I think the chances are that the "leopard spots and poppy seeds" on Mars will turn out to be actual evidence of life. People are naturally skeptical given the history of possible signs of life on other planets. Strap in: long thread ahead...

Skylink satellites seen on New Year's night in the sky over Colorado.

X-ray imagery of an ancient sandstone, this time a side-on view of sloping layers formed by sand grains (cyan and black) that avalanched down the steep faces of small underwater dunes. Small, heavy grains like pyrite (yellow) were trapped beneath many layers. Gratuitous beauty in sand! ⚒️

More than a meter of stacked fossil microbial mats in 3.22-billion-year-old sandstone! These are some of the oldest traces of life on Earth, and they are relatively unique for their age in that they can be seen and studied at outcrop scale. Moodies Group, Barberton greenstone belt, South Africa.⚒️

I saw this beautiful full moon with a halo tonight. The photograph was made more challenging by my dog who was more interested in getting her walk in than in astronomy or optics! @veritasium-science.bsky.social has a wonderful episode on this phenomenon: youtu.be/24GfgNtnjXc?...

And here's what this rock looks like to x-rays. The lower layer was squished into a wave-like shape by the overlying sand and later solidified by carbonate minerals. What remains tells us about how early microbes affected local iron and carbon cycles. R=Fe, G=Ca, B=Mg, white=Mn, cyan=K. ⚒️

Core from ~3.22 billion year old deltaic rocks, Moodies Group, South Africa. I hope to learn a lot about early life and environments on Earth from this and its sister samples, especially to compare with Martian deltaic environments of nearly the same age. Also, sedimentary structures are pretty!