POWERS OF ATTORNEY

        KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears
below hereby constitutes and appoints Mark McDonnell his or its true and lawful
attorney-in-fact, with full power of substitution, to sign any and all
instruments, certificates and documents that may be necessary, desirable or
appropriate to be executed on behalf of himself as an individual or in his
capacity as a direct or indirect general partner, member, director, officer or
manager of any partnership, corporation or limited liability company, pursuant
to section 13 or 16 of the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), and any and all regulations promulgated thereunder, and to file
the same, with all exhibits thereto, and any other documents in connection
therewith, with the Securities and Exchange Commission, and with any other
entity when and if such is mandated by the Exchange Act or by the Financial
Industry Regulatory Authority, granting unto said attorney-in-fact full power
and authority to do and perform each and every act and thing necessary,
desirable or appropriate, fully to all intents and purposes as he might or could
do in person, thereby ratifying and confirming all that said attorney-in-fact,
or his substitutes, may lawfully do or cause to be done by virtue hereof.  This
Power of Attorney shall remain in full force and effect with respect to each
undersigned person unless and until six months after such person is both no
longer a Managing Director of ARCH Venture Partners and no longer serving on the
board of directors of any portfolio company of any ARCH Venture Partners fund.

        IN WITNESS WHEREOF, this Power of Attorney has been signed as of the
29th day of January, 2019.

                                   ARCH VENTURE FUND IX, L.P.

                                   By:    ARCH Venture Partners IX, L.P.
                                                its General Partner

                                   By:    ARCH Venture Partners IX, LLC
                                                its General Partner

                                                By: /s/Keith Crandell
                                                    ----------------------------
                                                    Managing Director

                                   ARCH VENTURE PARTNERS IX, L.P.

                                   By:    ARCH Venture Partners IX, LLC
                                                its General Partner

                                                By: /s/Keith Crandell
                                                    ---------------------------
                                                    Managing Director

                                   ARCH VENTURE FUND IX OVERAGE, L.P.

                                   By:    ARCH Venture Partners IX Overage, L.P.
                                                its General Partner

                                   By:    ARCH Venture Partners IX, LLC
                                                its General Partner

                                                By: /s/Keith Crandell
                                                    ----------------------------
                                                    Managing Director

                                   ARCH VENTURE PARTNERS IX OVERAGE, L.P.

                                   By:    ARCH Venture Partners IX, LLC
                                                its General Partner

                                                By: /s/Keith Crandell
                                                    ----------------------------
                                                    Managing Director


                                   ARCH VENTURE PARTNERS IX, LLC

                                   By:     /s/Robert Nelsen
                                       ------------------------
                                       Managing Director


                                   /s/Keith Crandell
                                   -----------------
                                   Keith Crandell


                                   /s/Kristina Burow
                                   -----------------
                                   Kristina Burow


                                   /s/Clint Bybee
                                   --------------
                                   Clint Bybee


                                   /s/Robert Nelsen
                                   ----------------
                                   Robert Nelsen